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Introduction

The Asus ProArt (PA) series is primarily aimed at professional users and those doing colour critical work on their monitors. However, Asus have done a good job keeping the retail costs reasonable, and so the PA screens often provide a nice balance between performance and price. The PA248Q is a 24" standard gamut screen providing an alternative to models like Dell's U2412M and HP's ZR2440w. Asus do have wide gamut models available too (PA249Q) but the the PA248Q is aimed at those who don't want or need wide gamut support, and mainstream users who are interested in colour accuracy, but don't want the complications of wide gamut to contend with. The 16:10 aspect ratio and 1920 x 1200 resolution are provided by an IPS panel, offering the all-round performance we've come to expect from that technology. From a colour point of view the screen comes factory calibrated to ensure high levels of accuracy.

The "J" edition of the screen (PA248QJ) is the same, except that it also comes with a calibration system - a Spyder4 Express colorimeter and software, along with a monitor hood. This bundle provides users with an even higher level of control and accuracy where needed. We have the PA248QJ package with us for review, but the screen remains identical to the PA248Q so really this review can cover both versions available.

 



Specifications and Features

The following table gives detailed information about the specs of the screen:

Monitor Specifications

Size

24"WS

Panel Coating

Anti-glare (matte)

Aspect Ratio

16:10

Interfaces

1x DVI (HDCP), 1x HDMI, 1x D-sub, 1x DisplayPort

Resolution

1920 x 1200

Pixel Pitch

0.270 mm

Design colour

Matte black bezel, stand and base. Red trim to screen

Response Time

6ms G2G

Ergonomics

-5 / 20 Tilt, height, swivel and rotate adjustments

Static Contrast Ratio

1000:1

Dynamic Contrast Ratio

80 million:1

VESA Compatible

Yes 100mm

Brightness

300

Accessories

DVI cable, DisplayPort cable, VGA cable,  Power cord, USB 3.0 cable

PA248QJ also: monitor hood, Spyder4 Express calibration kit, cable tie

Viewing Angles

178 / 178

Panel Technology

e-IPS

Weight (net)

6.4Kg

Backlight Technology

W-LED

Physical Dimensions

(WxHxD with stand)
557.2 x 416.3 x 235 mm

Colour Depth

16.7m (6-bit + AFRC)

Refresh Rate

60Hz

Special Features

Factory calibration + report, 4x USB 3.0 ports, headphone jack, PiP and PbP. Calibration kit and hood (PA248QJ only)

Colour Gamut

Standard gamut
~72% NTSC, 100% sRGB

The Asus PA248QJ offers a decent set of connectivity options. There are HDMI, DVI, DisplayPort and D-sub (VGA) provided for video interfaces. It's nice to see HDMI provided for users who want to connect other devices, particularly external Blu-ray and DVD players, along with games consoles. The digital interfaces are HDCP certified for encrypted content as well.

There is also an audio out connection for connecting headphones if you wish to take the sound from the HDMI input but no integrated speakers on this model. There are also 4x USB 3.0 ports on the screen which are useful and it's nice to see the latest generation of USB used here.

Below is a summary of the features and connections of the screen:

Feature

Yes / No

Feature

Yes / No

Tilt adjust

DVI

Height adjust

HDMI

Swivel adjust

D-sub

Rotate adjust

DisplayPort

VESA compliant

Component

USB Ports

Composite

Card Reader

Audio connection

Ambient Light Sensor

HDCP Support

Touch Screen

MHL Support

Hardware calibration

Integrated Speakers

Uniformity correction

PiP / PbP



Design and Ergonomics


Above: front views of the screen. Click for larger versions.

The screen comes in an all-black design with matte plastics used for the bezel, stand and base. The bezel is nice and thin and measures ~18mm along all sides. In the top left hand corner, in a light grey font is a "ProArt" logo and in the bottom left hand corner is an HDMI logo. In the middle of the lower bezel is a shiny silver Asus logo as well. There is a thin red trim along the bottom bezel, as you can see from the above images.


Above: front views of the screen with added hood and calibration kit. Click for larger versions

The PA248QJ version of the screen is packaged with a removable hood and Spyder4 Express calibration kit, and is pictured above. Apart from that, the screen is the same as the PA248Q.


Above: views of the base of the stand. Click for larger versions.

The stand and base is made of matte black plastics and is rectangular in shape. It measures 235 x 280mm and provides a sturdy base for the screen as it sits on the desk. The stand rotates within the base when you move it side to side. The screen stays nice and steady on the desk and does not wobble.



Above: rear views of the screen. Click for larger versions.

The back of the screen is again matte black plastic. There is an Asus logo on the back, and the stand attaches in the middle, using a VESA 100 compliant attachment. You can remove the stand if you wish to wall or arm mount the screen.


Above: Side USB 3.0 ports and back of the screen VESA connection. Click for larger versions

The left hand edge of the screen (as viewed from the front) has 4x USB 3.0 ports for easy access which is a nice extra.

The screen offers a full range of ergonomic adjustments from the stand which is nice to see.


Above: full range of tilt adjustment shown. Click for larger versions.

The tilt adjustment affords you a good range of angles, and is smooth and easy to use. The full range of this adjustment is shown in the images above.


Above: Full range of height adjustment shown. Click for larger versions.

The height adjustment provides you a 100mm adjustment range to play with. At the lowest level, the bottom edge of the screen is 60mm from the top of the desk, and at maximum extension the bottom edge is 160mm from the desk. The movement is smooth but a little stiff to use, especially when lowering it.


Above: rotated view. Click for larger version

The side to side pivot adjustment is smooth and easy to use allowing you to angle the screen for different viewing positions easily. There is also a full rotate adjustment to switch between portrait and landscape modes, which is smooth but a little stiff to use.

A summary of the screens ergonomic adjustments is shown below:

Function

Range

Smoothness

Ease of Use

Tilt

Yes

Smooth

Easy

Height

100mm

Smooth

Little stiff

Swivel

Yes

Smooth

Easy

Rotate

Yes

Smooth

Little stiff

Overall

Good range of adjustments and all pretty easy to use, offering smooth movements

The screen materials and build are of a good quality and the design is nice in our opinion. There is a no audible noise from the screen during normal use even if you listen closely or use specific test images with a large concentration of text. The screen also stays nice and cool thanks to the W-LED backlight unit.
 


Above: interface and power connections on the back of the screen. Click for larger versions

The back of the screen has connections for DisplayPort, HDMI, DVI, VGA, audio output and USB upstream. On the other side is the normal power connection (kettle lead type) and an on/off switch. The screen has an integrated power supply so you only need to use the provided cable, and no external power bricks.

 



OSD Menu

      
Above: views of OSD operational buttons. Click for larger version

The OSD is accessed through a series of buttons on the bottom right hand edge of the front bezel as shown above. As well as the normal buttons, there is also a small 5-way navigation stick/button which allows for quick and easy scrolling through the available settings and is intuitive and easy to use.

There is quick launch access from the '1' button to the brightness control, and from the '2' button for the contrast control as shown above. You can actually change the function of these quick access buttons from within the main OSD menu if you wish.

There is also quick access to switch between the preset modes of the screen with the options above available.

There is also an input selection button which quickly and easily cycles through the inputs of the monitor, flashing a small label in the top left hand corner of the screen briefly as you cycle through the options and confirming your current input selection.

The main OSD menu is split into 7 sections shown down the left hand side. As you scroll up and down to select a section, the options available are shown on the right hand side. Once you enter a section, you can then change the settings shown. The first section is the 'Splendid' preset mode menu with the options shown above available.

The 'Color' section provides options for brightness, contrast and various aspects of the colour and image controls. Here there are options to select the colour temperature and gamma as well and in certain presets you can gain access to the RGB channels for calibration.

The 'image' section has a few of the advanced features available, including the 'Trace Free' setting for response time control, the aspect ratio control (options for full, 1:1 and 4:3) and the ASCR dynamic contrast ratio control.

There is a PiP and PbP function available on this screen and the above section of the OSD lets you control the settings related to that.

The 'input select' section allows you to switch between the various video inputs.

The 'system setup' section gives you control over various aspects of the OSD itself. You can also turn the power LED off if you want here.

The final section allows you to change the function of the '1' and '2' shortcut keys if you like, to something you might use commonly.

All in all the OSD menu had a good range of options with plenty to control. The navigation was quick and easy, and the small control stick made it all very easy and intuitive to use.

 


Power Consumption

State and Brightness Setting

Manufacturer Spec (W)

Measured Power Usage (W)

Factory Default (50%)

<45W

29.8

Calibrated (20%)

-

24.0

Maximum Brightness (100%)

-

40.0

Minimum Brightness (0%)

-

20.5

Standby

<1W

0.5

The table above shows the manufacturer quoted power usage (where applicable), and the actual power usage measured in our lab. Out of the box the screen used 29.8W of power while at its default brightness setting which was 50%. At the lowest setting this was measured at 20.5W. Once calibrated we had reached a power consumption of 24.0W which had been once the screen had been set to achieve a luminance of 120 cd/m2. During standby the screen uses 0.5W of power. We have plotted the results of these measurements on the graph below.



Panel and Backlighting

Panel Manufacturer

LG.Display

Colour Palette

16.7 million

Panel Technology

e-IPS

Colour Depth

6-bit + AFRC

Panel Module

LM280WU8-SLA2

Colour space

Standard Gamut

Backlighting Type

W-LED

Colour space coverage (%)

71% NTSC, 74.3% Adobe RGB, 95.8% sRGB

Panel and Colour Depth

The Asus PA248Q utilises an LG.Display LM240WU8-SLA2 e-IPS panel which is capable of producing 16.7 million colours. This is done with a 6-bit colour depth and additional Advanced Frame Rate Control (FRC) stage (6-bit + AFRC). The panel is confirmed when accessing the factory menu as shown below (hold 'menu' while powering the screen on > press 'menu' once screen is on):

Panel Coating

The screen coating on the PA248Q is an old style AG coating from IPS panels. It is an older panel and so the AG coating could be described as being 'heavy' or grainy. Some people find this to be problematic when viewing a lot of light content, particularly white backgrounds of office documents and spreadsheets. Many people though do not find it an issue and it's been used on IPS panels for many years. It should be noted that some modern IPS panels have reverted to a lighter, "cleaner" AG coating instead.
 

Backlighting and Colour Gamut

The screen uses a White-LED (W-LED) backlight unit which has become very popular in today's market. This helps reduce power consumption compared with older CCFL backlight units and brings about some environmental benefits as well. The W-LED unit offers a standard colour gamut which is approximately equal to the sRGB colour space. Studying the details panel spec sheet confirms a colour space coverage of 71% NTSC, 74.3% Adobe RGB and 95.8% sRGB. Anyone wanting to work with wider colour spaces would need to consider wide gamut CCFL screens, or perhaps the new range of GB-LED backlit displays.


Backlight Dimming and Flicker

We tested the screen to establish the methods used to control backlight dimming. Our in depth article talks in more details about a common method used for this which is called Pulse Width Modulation (PWM). This in itself gives cause for concern to some users who have experienced eye strain, headaches and the likes as a result of the flickering backlight caused by this technology. Previously we have used a camera based method as described in the article to capture results at brightness settings of 100, 50 and 0. We now have a more advanced photosensor +  oscilloscope system which will allow us to measure backlight dimming control with more accuracy and ultimately more ease. These tests allow us to establish

1) Whether PWM is being used to control the backlight
2) The frequency at which this operates if used
3) Whether a flicker may be introduced or potentially noticeable at certain settings.

The higher this frequency, the less likely you are to see artefacts and flicker. The duty cycle (the time for which the backlight is on) is also important and the shorter the duty cycle, the more potential there is that you may see flicker. As a backlight is dimmed, the duty cycle typically becomes shorter and so flicker may be more apparent at lower settings. Please remember that not every user would notice a flicker from the backlight but it is something to be wary of. It is also a hard thing to quantify as it is very subjective when talking about whether a user may or may not experience the side effects. We are able to at least measure the frequency of the backlight using this method and tell you whether the duty cycle is sufficiently short at certain settings that it may introduce a flicker to those sensitive to it.

100%                                                  50%                                                  0%

Scale = 1 horizontal grid = 5ms

 

Our tests confirm the use of PWM for backlight dimming. At a maximum 100% brightness there is a constant voltage applied to the backlight and it remains continuously lit, as shown by the steady, flat line. As you reduce the brightness however the backlight is controlled by PWM. From a brightness setting of 80% and below the modulation is 100%, i.e. the backlight is turned completely off and there is no light output while in the 'off' stage. This is evident from the oscillographs where the troughs reach down to 0V on the vertical scale (i.e. no light output). From there, with the modulation remaining constantly at 100% throughout the brightness adjustment range down to the 0% setting, the light output is controlled through a reduction in the duty cycle, that being the time for which the backlight is in an 'on' state. This gets progressively shorter until you reach a 0% brightness setting. This can be seen in the oscillographs as the upper peaks are shorter at 0% brightness than at 50% brightness. The PWM operates at a fixed frequency of 180Hz. Given the relatively low frequency and the use of a W-LED backlight unit, this may present problems to some users who are susceptible to flicker and eye issues. If you're looking for a screen without PWM then please see our flicker free monitor database.

Pulse Width Modulation Used

Yes

Cycling Frequency

180Hz

Possible Flicker at

 

100% Brightness

No

50% Brightness

Yes

0% Brightness

Yes

 


Testing Methodology

An important thing to consider for most users is how a screen will perform out of the box and with some basic manual adjustments. Since most users won't have access to hardware colorimeter tools, it is important to understand how the screen is going to perform in terms of colour accuracy for the average user.

I restored my graphics card to default settings and disabled any previously active ICC profiles and gamma corrections. The screen was tested at default factory settings using the DVI interface, and analysed using an X-rite i1 Pro Spectrophotometer (not to be confused with the new i1 Display Pro colorimeter) combined with LaCie's Blue Eye Pro software suite. An NEC branded and customised X-rite i1 Display 2 colorimeter was also used to verify the black point and contrast ratio since the i1 Pro is less reliable at the darker end.


Targets for these tests are as follows:

  • CIE Diagram - validates the colour space covered by the monitors backlighting in a 2D view, with the black triangle representing the displays gamut, and other reference colour spaces shown for comparison

  • Gamma - we aim for 2.2 which is the default for computer monitors

  • Colour temperature / white point - we aim for 6500k which is the temperature of daylight

  • Luminance - we aim for 120 cd/m2, which is the recommended luminance for LCD monitors in normal lighting conditions

  • Black depth - we aim for as low as possible to maximise shadow detail and to offer us the best contrast ratio

  • Contrast ratio - we aim for as high as possible. Any dynamic contrast ratio controls are turned off here if present

  • dE average / maximum - as low as possible. If DeltaE >3, the color displayed is significantly different from the theoretical one, meaning that the difference will be perceptible to the viewer. If DeltaE <2, LaCie considers the calibration a success; there remains a slight difference, but it is barely undetectable. If DeltaE < 1, the color fidelity is excellent.



Default Performance and Setup

Default settings of the screen were as follows:

Monitor OSD Option

Default Settings

Brightness

50

Contrast

80

Preset Mode

Standard

RGB

n/a

Gamma

2.2

Color Temp

6500k


Asus PA248Q - Default Settings

 


 

Default Settings

luminance (cd/m2)

178

Black Point (cd/m2)

0.21

Contrast Ratio

846:1

 

Default setup of the screen was reasonable in some regards, but a little lacking in some areas. When you first connect up the screen you at least had a reasonable brightness setting (50% in the OSD) which meant it was not overly bright or difficult to use. That's quite rare for desktop monitors really, which normally come out of the box with an excessively bright setting. The image did feel a little cool perhaps but overall it looked pretty good to the naked eye. The screen is in the 'standard' preset mode by default, so we will test the factory calibrated sRGB mode in a moment as well.

 

The CIE diagram on the left of the image confirms that the monitors colour gamut (black triangle) is a very close match to the sRGB reference (orange triangle). This confirms the use of a standard gamut W-LED backlight. There is some slight over-coverage in greens and some slight under-coverage in reds, but nothing significant at all.

 

 

Default gamma was recorded at 2.4 average, leaving it a little out with a 8% deviance from the target of 2.2 which wasn't too bad but not ideal. This was farthest out in the lighter grey shades. White point was too cool compared with the 6500k target, being measured at 7739k with a 19% deviance.

 

Luminance was recorded at a modest 178 cd/m2 which is still a little too high for prolonged general use, but at least is not blinding. The screen was set at a default 50% brightness in the OSD menu and is easy to change of course to reach a more comfortable setting either more or less bright, depending on your needs. The black depth was 0.21 cd/m2, giving us a good static contrast ratio of 846:1. Colour accuracy was pretty good as well with an average dE of 2.7, and a maximum of 6.6. Testing the screen with various gradients showed very smooth transitions with no sign of any banding thankfully. There was some very slight gradation evident in darker tones as you will see from most monitors and you could just about pick out the FRC if you looked very closely. Not something you'd notice in day to day use at all though and it is well implemented here.

 


Factory Calibration

The PA248Q comes factory calibrated in its sRGB preset mode. To ensure that each PA248Q produces the most accurate and consistent colour, Asus carefully measure its ∆E (dE) and gamma value and track its grey-scaling. It also supports both Gamma 2.2 for PC and Gamma 1.8 modes for Mac, offering users more flexibilities to work with. Each screen has been calibrated to minimize colour difference to ∆E (Delta E) of less than 5. It comes packaged with a unique calibration report for your particular screen as well, as shown below.


Above: factory calibration report, click for larger version

We wanted to measure the performance in this mode as well. The default settings of the screen in the sRGB preset were as follows. You will note you have far more restricted control over the OSD here, with brightness being the only setting you can change.

Monitor OSD Option

Default Settings

Brightness

50

Contrast

n/a

Preset Mode

sRGB

RGB

n/a

Gamma

n/a

Color Temp

n/a


Asus PA248Q - Default Factory Calibration, sRGB

 

 

Default Settings, Factory calibration

luminance (cd/m2)

171

Black Point (cd/m2)

0.19

Contrast Ratio

906:1

 

The results were not really that different to the 'standard' mode to be honest. The gamma remained at 2.4 average with a slightly higher deviance even at 10%. The white point was also still too cool with a 19% deviance (7709k) as we had seen before. Colour accuracy had improved a little with a dE average of 2.7 still, but reducing some of the highest variances, bringing maximum dE down to 5.2. The contrast ratio had also improved a little to 906:1 which was very good for an IPS panel. All in all, we were hoping for a slightly better gamma and white point setup to be honest from this factory calibration, although the colour accuracy lived up to its promises.

 

 


Colour Temperatures

 

 

The PA248Q features a selection of colour temperature presets within the OSD 'Color' menu as shown above. We measured the screen with the X-rite i1 Pro spectrophotometer in each of the available modes to establish their colour temperature / white point out of the box, compared with the target. All other settings were left at factory defaults and no ICC profile was active. The results are recorded below:

 

Selected Preset Mode (k)

Measured Colour Temperature (k)

Deviance from target (k)

Deviance

5000

5233

+233

+4.7%

5500

5987

+487

+8.9%

6500

7857

+1357

+20.9%

9300

14,695

+5395

+58.0%

 

 

There are only 4 colour temperature modes available from the OSD. The warmer settings of 5000k and 5500k were quite close to their target temperatures in practice, although the 6500k showed a fairly high deviance of ~20.9%, being too cool unfortunately. The 9300k mode was far too cool at 14,695k, and gave a very large deviance of 58%. It would have been nice to see a slight more accurate setup here, especially for the widely used 6500k temperature. It might also have been useful to see a couple more options perhaps. As it stands, there's no easy way to obtain a white point that close to 6500k without a calibration device. The 5500k setting would probably be the best option as it is more like 5987k in reality, and just a little too warm.

 

 

 

Calibration

 

We used the X-rite i1 Pro spectrophotometer combined with the LaCie Blue Eye Pro software package to achieve these results and reports. An NEC branded and customised X-rite i1 Display 2 was used to validate the black depth and contrast ratios due to lower end limitations of the i1 Pro device.

 

Monitor OSD Option

Calibrated Settings

Brightness

23

Contrast

80

Preset Mode

User 1

RGB (Gain)

50, 47, 44

Gamma

2.2

Color Temp

6500k


Asus PA248Q - Calibrated Settings, User Preset

  
 

 

Calibrated Settings, User Preset

luminance (cd/m2)

120

Black Point (cd/m2)

0.14

Contrast Ratio

857:1

 

We first of all reverted to the 'user 1' preset mode in the OSD menu which would allow us access to the individual RGB channels. There is also a 'user 2' mode if you want to set up another preset to different settings. Adjustments were made during the process to the brightness control, and to the RGB channels (gain) as shown in the table above. This allowed us to obtain an optimum hardware starting point and setup before software level changes would be made at the graphics card level. This would help preserve tonal values and limit banding issues. After this we let the software carry out the LUT adjustments and create an ICC profile.

 

Average gamma had been corrected to 2.2, correcting the default 8% deviance we'd found out of the box in the standard preset mode and leaving only a small 1% deviance. The white point was also corrected to 6530k, sorting out the pretty large 19% deviance from before. Luminance had also been improved thanks to the adjustment to the brightness control, now being measured at 120 cd/m2. This gave us a calibrated black depth of 0.14 cd/m2, and a static contrast ratio of 857:1 which was very good for an IPS panel.

 

Colour accuracy was a problem though and despite numerous attempts, and numerous calibration tools, we were unable to obtain a satisfactory result. We tried different OSD settings and each time it seems the resulting colours were not as accurate as they should be. This left us with high dE differences but it was not clear why this was the case. This is a shame, as the 'user' presets given you access to the 6-axis colour adjustment which should in theory allow you more control over the hardware settings. As it was, the issues in this preset meant these user modes were largely pointless. Having seen other tests of this screen in the past, we aren't the only ones who've had this issue.

 

We wanted to see what we could do in the other preset modes, hoping that we could achieve better results.

 

 

Monitor OSD Option

Calibrated Settings

Brightness

20

Contrast

80

Preset Mode

Standard

RGB (Gain)

n/a

Gamma

2.2

Color Temp

6500k


Asus PA248Q - Calibrated Settings, Standard Preset

  
 

 

Calibrated Settings,
Standard preset

luminance (cd/m2)

120

Black Point (cd/m2)

0.14

Contrast Ratio

856:1

 

We then carried out a software calibration in the 'standard' preset mode. In this mode you have more limited control over the OSD settings, with the RGB channels not being available. We adjusted the brightness control as suggested in the process, but then let the calibration device carry out the rest of the corrections and adjustments at the graphics card LUT level.

 

Gamma, white point and luminance targets had all been met nicely as you can see. Contrast ratio was still very good at 856:1 which was pleasing. Best of all colour accuracy had also been corrected very well, with an average dE of only 0.4. LaCie would consider colour fidelity to be excellent. Testing the screen with various colour gradients showed smooth transitions on the most part, with some slight banding introduced in the darker tones due to the adjustments made at the graphics card level. This preset mode did seem to allow for a better calibration for some reason, and so should probably be used if you have access to a calibration device.

 

You can use our settings and try our calibrated ICC profile if you wish, which are available in our ICC profile database. Keep in mind that results will vary from one screen to another and from one computer / graphics card to another.

 

 

 

Calibration Performance Comparisons


 

The comparisons made in this section try to give you a better view of how each screen performs, particularly out of the box which is what is going to matter to most consumers. When comparing the default factory settings for each monitor it is important to take into account several measurement areas - gamma, white point and colour accuracy. There's no point having a low dE colour accuracy figure if the gamma curve is way off for instance. A good factory calibration requires all 3 to be well set up. We have deliberately not included luminance in this comparison since this is normally far too high by default on every screen. However, that is very easily controlled through the brightness setting (on most screens) and should not impact the other areas being measured anyway. It is easy enough to obtain a suitable luminance for your working conditions and individual preferences, but a reliable factory setup in gamma, white point and colour accuracy is important and not as easy to change accurately without a calibration tool.

 

From these comparisons we can also compare the calibrated colour accuracy, black depth and contrast ratio. After a calibration the gamma, white point and luminance should all be at their desired targets.

 

 

Default setup of the PA248Q was not perfect, but not too bad in some areas. There was a small variance in the gamma at 8% which could only really be corrected properly through the use of a colorimeter. There are no controls to tweak the gamma at a finite level in the OSD unfortunately. White point was the main issue with the out-of-the-box setup, being a rather large 19% out from the target and being too cool (blue) by default. Again this wasn't easy to correct through the OSD. You could obtain a white point at ~6000k if you switch to the 5500k preset mode, which brings it closer to the 6500k target, but now being a little too warm. Colour accuracy was not too bad with a dE average of 2.7 out of the box which was reasonable at least.

 

 

 

The calibrated black depth and contrast ratio of the screen were very good for an IPS panel. The 856:1 contrast ratio was one of the higher figures we'd seen from IPS technology really and so we were pleased with this result. We had already seen a good solid performance from this LG.Display LM240WU8 panel from its use in the Dell U2412M (947:1) and HP ZR2440w (935:1) which had reached a slightly higher calibrated contrast ratio than the Asus, but not by much. Of course IPS can't compete with the mega high contrast ratios of modern AMVA panels which reach up to 2000 - 3000:1 as you can see. Nevertheless a decent enough performance from the PA248Q here considering its panel technology of choice.

 

 

 


Contrast Stability and Brightness

We wanted to see how much variance there was in the screens contrast as we adjusted the monitor setting for brightness. In theory, brightness and contrast are two independent parameters, and good contrast is a requirement regardless of the brightness adjustment. Unfortunately, such is not always the case in practice. We recorded the screens luminance and black depth at various OSD brightness settings, and calculated the contrast ratio from there. Graphics card settings were left at default with no ICC profile or calibration active. Tests were made using an NEC branded and customised X-rite i1 Display 2 colorimeter. It should be noted that we used the BasICColor calibration software here to record these, and so luminance at default settings may vary a little from the LaCie Blue Eye Pro report.

OSD Brightness

Luminance
(cd/m2)

Black Point (cd/m2)

Contrast Ratio
( x:1)

100

290.53

0.34

854

90

267.34

0.31

862

80

244.27

0.28

872

70

222.92

0.26

857

60

199.88

0.23

869

50

177.74

0.21

846

40

158.38

0.18

880

30

140.28

0.16

877

20

121.90

0.14

871

10

103.41

0.12

862

0

84.75

0.10

848

 

Total Luminance Adjustment Range (cd/m2)

205.78

Brightness OSD setting controls backlight?

Total Black Point Adjustment Range (cd/m2)

0.24

Average Static Contrast Ratio

863:1

PWM Free? 

Recommended OSD setting for 120 cd/m2

19

The luminance range of the screen was good. At the maximum brightness setting the screen reached 290.53 cd/m2, which was only slightly lower than the specified 300 cd/m2 maximum. At the lower end of the adjustment range you could reach down to 84.75 cd/m2. This should be ok for most users, but perhaps might not be dark enough for some who want to use the screen in very low lighting conditions. The total adjustment range of 205.78 cd/m2 was good, but we would have perhaps preferred a lower minimum brightness and a lower maximum brightness overall. As we discussed earlier, the backlight dimming is achieved through the use of  PWM dimming and so those prone to any issues with backlight flickering should be cautious.

We have plotted the luminance trend on the graph above. The screen behaves as it should, with a reduction in the backlight intensity controlled by the reduction in the OSD brightness setting. This was pretty much a linear relationship.

Average contrast ratio measured was 863:1 which was very good for an IPS panel. This remained nice and stable across the brightness adjustment range as shown above.

 


Dynamic Contrast

The Asus PA248Q features a dynamic contrast ratio (DCR) control, which boasts a spec of 80,000,000:1 (80 million:1). Dynamic contrast ratio involves controlling the backlight of the screen automatically, depending on the content shown on the screen. In bright images, the backlight is increased, and in darker images, it is decreased. We have come to learn that DCR figures are greatly exaggerated and what is useable in reality is often very different to what is written on paper or on a manufacturers website.

For this test we would use a colorimeter to record the luminance and black depths at the two extremes. Max brightness would be recorded on an almost all white screen. Black depth would be recorded on an almost all black screen. In real use you are very unlikely to ever see a full black or full white screen, and even our tests are an extreme case to be honest. Carrying out the tests in this way does give you a good indication of the screens dynamic contrast ratio in real life situations however.

The DCR feature is available in the Scenery and Theater preset modes. It has a simple setting for off and on, and is labelled as "ASCR" (Asus Smart Contrast Ratio) in the 'Image' section of the OSD.

 

Dynamic Contrast

Specified DCR Range

80 Million:1

Available in Presets

Scenery, Theater

Setting Identification / Menu option

ASCR

Settings

off / on

Measured Results

Scenery

Theater

Default Static Contrast Ratio

811:1

493:1

Max luminance (cd/m2)

293.86

137.41

Min Black Point (cd/m2)

0.37

0.37

Max Dynamic Contrast Ratio

794:1

371:1

Useable DCR in practice

No

No

Backlight turned off for 100% black

Yes

Yes

We tested the DCR feature in both of the preset modes. By default the Scenery preset mode gave us a static contrast ratio similar to that which we'd measured in the standard default preset mode. However, with DCR enabled the brightness of the screen was very high at 293.86 cd/m2. The DCR seemed to do nothing at all though when switching between an almost all-white and almost all-black screen which was a shame. If you switch to a 100% black image , you can see the backlight starts to dim, and after 5 seconds it is turned off completely. Given that you're unlikely to ever get a 100% black image in practice, this feature seems pointless and is more of a marketing number than anything else. The high 80 million:1 spec is achieved in the lab when the backlight is turned off, but in day to day use you're never going to be able to use it. The 'Theater' mode was a similar story, with the DCR not doing anything in practice. In fact the static contrast ratio was crushed quite a lot in this mode to around 400:1 so it wasn't very desirable. Again the backlight is turned off completely, this time after ~10 seconds but again useless in practice.

 


Viewing Angles


Above: Viewing angles shown from front and side, and  from above and below. Click for larger image

Viewing angles of the PA248Q were very good as you would expect from an IPS panel. Horizontally there was very little colour tone shift until wide angles past about 45. A slight darkening of the image occurred horizontally from wider angles as you can see above as the contrast shifted slighting. Contrast shifts were slightly more noticeable in the vertical field where a slight pink-ish hue also appeared, but overall they were very good. The screen offered the wide viewing angles of IPS technology and was free from the very restrictive fields of view of TN Film panels, especially in the vertical plane. It was also free of the off-centre contrast shift you see from VA panels and a lot of the quite obvious gamma and colour tone shift you see from some of the modern AMVA and PVA offerings. All as expected really from a modern IPS panel. On a black image there is a characteristic IPS white glow introduced to the image when viewed from a wide angle. This may be problematic to some users working with a lot of dark content, or in darkened room conditions.



Panel Uniformity

We wanted to test here how uniform the brightness and colour temperature was across the screen, as well as identify any leakage from the backlight in dark lighting conditions. Measurements of the luminance and colour temperature were taken at 35 points across the panel on a pure white background. The measurements for luminance were taken using BasICColor's calibration software package, combined with the NEC customised X-rite i1 Display 2 colorimeter with a central point on the screen calibrated to 120 cd/m2. Measurements for colour temperature (white point) were taken using BasICColor software and the i1 Pro spectrophotometer which can more accurately measure white points of different backlighting technologies. The below uniformity diagram shows the difference, as a percentage, between the measurement recorded at each point on the screen, as compared with the central reference point.

It is worth noting that panel uniformity can vary from one screen to another, and can depend on manufacturing lines, screen transport and other local factors. This is only a guide of the uniformity of the sample screen we have for review.
 


Uniformity of Luminance

The luminance uniformity of the screen was moderate overall. There did seem to be some darker regions in the top corners, where luminance dropped by a maximum of 22.45%, down to around 98 cd/m2 in the most extreme case. The bottom left hand corner was also a little brighter than than the middle of the screen, at ~4% more, and 125 cd/m2. Nothing too severe, but not optimum if you were doing colour critical work.
 


Uniformity of White Point / Colour Temperature

The colour temperature uniformity was measured based on a centrally calibrated 6500k point. As you can see, the colour temperature was very stable across the screen, with only very small differences of a few percent. This should provide a good uniformity when working with colours and gradients and presented no problems.



Backlight Leakage


Above: All black screen in a darkened room. Click for larger version

As usual we also tested the screen with an all black image and in a darkened room. A camera was used to capture the result. There was no obvious backlight bleeding at all to the naked eye and the uniformity looked very good, even in a darkened room. The camera captured some slight clouding from the corners, but this was very minimal and not something which you should notice in practice.

 


General and Office Applications

The 1920 x 1200 resolution and 24" screen size give a nice decent area in which to work and the vertical resolution is a little more than the wide range of 16:9 aspect 24" models (1920 x 1080) out there in the market. A lot of people prefer this extra vertical area and it is useful for office applications we think. You may want to consider the fact that high resolution 27" 2560 x 1440 models are becoming increasingly available and so the difference in desktop size is certainly noticeable coming from a 27" screen like that. Nevertheless, the 24" 1920 x 1200 resolution should be adequate for many users. The screen offered a comfortable 0.27mm pixel pitch which delivered easy to read text at a nice size, in my opinion. The resolution is certainly big enough for side by side split screen working as well in many cases.

The digital DVI interface offered a slightly sharper image quality than the D-sub analogue interface and so should be used wherever possible for your PC connection. The old style 'heavy' AG coating means that the white backgrounds of office applications don't look as 'clean' as some other panels we've tested, although it doesn't appear overly aggressive here to be honest.  Default luminance of the screen was recorded at 178 cd/m2 which is a bit too high for prolonged office use. You will want to turn the screen down probably to around 19 - 20% brightness to achieve a luminance of around 120 cd/m2. Those wanting to use the screen in darker room conditions and at a luminance lower than this can do so through further adjustment to this setting, down to around 85 cd/m2 minimum which might be restrictive in some cases, but should be adequate for most users. The backlight dimming is achieved through the use of PWM and so those affected by flicker or eye issues should be cautious when considering this screen.

There is no specific preset mode available for reading or internet use, or anything like that, so you will want to set up one of the other modes to suit. The default white point is a little too cool unfortunately, with no easy way to correct it without a calibration device. Reverting to the 5500k mode  in the OSD menu might be preferable as it is closer to the 6500k target, but a little warmer at ~6000k, and so might be more comfortable for reading and office work (warmer tends to be a little easier on the eye). Gamma is also a little out from the 2.2 target and again there's no easy way to correct this without a calibration device. The factory calibrated sRGB mode isn't really any better sadly, despite the marketing hype. If you bought the PA248QJ version of the screen the packaged Spyder4 device and software should allow you to obtain a more accurate setup though thankfully. Obviously it can also be paired with any other calibration package you might want to buy or already have.

The screen features 4x USB 3.0 ports which is useful, and the stand provides a very wide range of adjustments which is pleasing. There are no other added functions such as ambient light sensors, card readers or human motion sensors here. Asus do have their own "Quick Fit" grid which is accessible by pressing the 5-axis control stick button. This pops up a series of different sized grids on the screen to allow you to check the sizes of your work more accurately.


Above: photo of text at 1920 x 1200 (top) and 1680 x 1050 (bottom)

The screen is designed to run at its native resolution of 1920 x 1200 and at a 60Hz recommended refresh rate. If you want you are able to run the screen outside of this resolution of course. We tested the screen at a lower 1680 x 1050 resolution while maintaining the same aspect ratio (16:10) to see how the screen handles the interpolation of the resolution. At native resolution the text was sharp as you can see from the top photograph. When you switch to a lower resolution the text is larger of course but maintains much of its sharpness and does not look overly blurry. There was fairly low levels of overlap of the pixels and text was still very readable. Native resolution is recommended where possible of course but the screen can interpolate lower resolutions nicely.

 


Responsiveness and Gaming

The PA248Q is rated by Asus as having a 6ms G2G response time which implies the use of overdrive / response time compensation (RTC) technology, used to boost pixel transitions across grey to grey changes.  The part being used is the LG.Display LM280WU8-SLA2 e-IPS panel. Have a read about response time in our specs section if you need additional information about this measurement.

There is a user controllable option in the OSD for the overdrive function, labelled as 'Trace Free'. There are settings in steps of 20 between 0 and 100. We will first test the screen using our thorough response time testing method. This uses an oscilloscope and photosensor to measure the pixel response times across a series of 20 different transitions, in the full range from 0 (black) to 255 (white). This will give us a realistic view of how the monitor performs in real life, as opposed to being reliant only on a manufacturers spec. We can work out the response times for changing between many different shades, calculate the maximum, minimum and average grey to grey (G2G) response times, and provide an evaluation of any overshoot present on the monitor.

We use an ETC M526 oscilloscope for these measurements along with a custom photosensor device. Have a read of our response time measurement article for a full explanation of the testing methodology and reported data.


Trace Free Setting Comparison

We first of all tested the screen with Trace Free turned off, at a setting of 0. As you can see from the results in this sample of measurements, the response time was not that great. Average G2G was only 13.6ms which wasn't that good and the rise times in the upper right hand region (changes from dark to light shades) were quite a lot slower than the fall times (changes from light to darker tones). Some ranged up around 20ms which was pretty poor. At least at this setting there was no RTC overshoot at all, although the response times were too slow really for our liking.


Transition: 50-255-50 (Trace Free 0)
(scale = 20ms)

Above is a typical response time graph for Trace Free 0, showing smooth transitions between the start and end points, freedom from any overshoot spikes, but a slower rise time than fall time.

If we change up to the Trace Free setting of 20 there is some improvement with the response times. The average G2G response time improves to 10ms from 13.6ms which is better, and there's some noticeable improvements in the rise times. Where this has improved the most in this measurement sample (the transition from 0 - 50), the response time has improved from 20.1ms (Trace Free 0) to 6.8ms (Trace Free 20). However, in doing so, a large RTC error of 40.2% has been introduced, causing a large overshoot of the desired shade. This Trace free setting of 20 seems to have boosted the rise times a little, but some transitions between darker shades now show some overshoot as a result. It's not a massive amount and on the whole there's no major issue.



Transition: 0-50-0 (Trace Free 20)
(scale = 20ms)

The above graph shows the 0-50-0 transition where you can see the overshoot spike on the rise time clearly (40.2% overshoot).

Switching up to the next setting of 40 showed another slight improvement in response time, with G2G average now 9.1ms. There was slightly more overshoot in some transitions, but at a low level of only 4 - 5%. Some dark transitions continued to show a significant overshoot where pixel response times had been improved most significantly. For example the 0-50 transition still showed an RTC error of 49.5% here which was high. This setting did seem to offer a slight improvement over Trace Free 20, without much real negative impact in the form of overshoot.

Trace Free 60 was a fairly drastic change from 40, but it was too aggressive sadly. The response times had been improved quite a lot by ~33%, with an average G2G of 6.8ms now. However, the RTC errors were becoming very problematic and noticeable in practice. More large errors of 20-40% crept in, particularly in the rise times where response times had been boosted the most from the overdrive impulse. We felt the additional improvement in response times was not worth it at the cost of the noticeable overshoot problems at this setting. The setting of 40 seemed an optimum balance we felt.


Transition: 150-255-150 (Trace Free 60)
(scale = 20ms)

As an example, the above graph shows the 150-255-150 transitions, where you can see some overshoot on both the rise and fall times.

The Trace Free setting of 80 only made the overshoot problems worse. There was a slight drop in response times, now down to 6.1ms, but the overshoot was even more apparent and at a higher level. In the worst cases in this sample, the RTC error was up as high as 60%. This mode should be avoided as a result.

Finally it was a similar story when pushing the Trace free setting all the way up to 100. Response times dropped again to 5.4ms now, even below the quoted 6ms G2G average from the manufacturer. However the RTC overshoot was disastrous, with some transitions showing up as high as 92.6%! Again, avoid this mode as the overshoot is just too problematic.


Transition:0-150-0 (Trace Free 100)
(scale = 20ms)

Here is the graph from the worst example of overshoot, with a massive spike on the rise time of 92.6%.

Having established that Trace Free 40 seemed to provide an optimum performance and balance, we carried out some more thorough measurements.

Trace Free 40 Detailed

We  carried out a further sample set of measurements in the Trace free 40 setting to get an even more complete view of the response times of the panel. Average G2G response time was a little lower than we'd seen from our small sample set in the previous section, now being measured at 8.4ms G2G which was moderate. The average rise (changes from dark to light shades) and average fall (changes from light to dark shades) times was identical at 8.4ms as well, showing a fairly consistent performance overall. The response times were lowest where the shades were close together, for example in the best case from a change from 150-200 at 4.6ms. However, these boosted response times were not without issue unfortunately...

The instances where response times were lowest unfortunately introduced some overshoot. In the most extreme case this was 49.5% (0-50), but on the most part it was around 15 - 20% which was noticeable, but not too severe. The overshoot only seemed a problem for the transitions between similar shades, and the more extreme changes (e.g. 0 - 255) were slower, but showed no overshoot. If the overshoot proves troublesome for your uses, you can always switch down to TF20 if you like, which should cut it down somewhat, but at the cost of slightly slower response times. Anything higher than TF40 introduces more noticeable overshoot so should probably be avoided.

As we begin to measure more screens with the oscilloscope system we can begin to plot them on a graph like the above for easy comparison. This shows you the lowest, average and highest G2G response time measurement for each screen. The Asus PA248Q performed quite similarly to the other IPS screens we've tested here. It wasn't quite as fast as the new Dell U series screens, but those had shown some far more problematic overshoot problems unfortunately. The Asus was faster than the AMVA based BenQ GW2760HS but couldn't keep up of course with the very fast gamer-orientated Asus VG278HE.

 

Motion Tests

The screen was also tested using the chase test in PixPerAn. As a reminder, a series of pictures are taken on the highest shutter speed and compared, with the best case example shown. This should only be used as a rough guide to comparative responsiveness, but is handy for a comparison between the different Trace Free settings and between different screens.

Motion Tests at Each Trace Free Setting (0 - 100)

Above is a comparison of the perceived motion performance in each of the Trace Free (TF) modes. This confirms what we had seen with our oscilloscope measurements of response time and RTC overshoot as well as you can see. The settings from 0, 20 and to 40 show a slight improvement in the moving image which you can see with the naked eye as you switch between each mode. There is a slightly less pronounced motion blur as you increase the setting up to TF40. In this mode, there are low levels of blur to the moving car, and no obvious overshoot problems in this test. We know from our oscilloscope measurements that some transitions which are close together can produce some moderately high levels of overshoot, but they aren't picked out in these PixPerAn tests.

As you move up to TF60, a dark overshoot artefact is introduced and noticeable to the naked eye. Behind the white speech bubble and yellow head is a dark trail which can be a little distracting. It's not horrible, but it does mean TF60 is a little worse than TF40 in our opinion for moving images and gaming. TF80 and TF100 show more pronounced overshoot, where the trails become darker, and in the case of the maximum setting, also show a pale halo. The overshoot in these modes is very distracting and obvious and so should be avoided.
 

Display Comparisons


24"WS 6ms G3G LG.Display e-IPS (Trace Free = 40)


24" 8ms G2G LG.Display e-IPS


24" 6ms G2G LG.Display e-IPS (Video OverDrive = On)

We can compare the PA248Q first of all against two other 24" IPS screens we have tested, using the same LM240WU8 panel in fact. These are of course logical competitors to the PA248Q, although the positioning of each screen does vary a little by manufacturer. The Asus seems to be more geared at colour enthusiasts and higher end work, although the other screens use the same panel and so ultimately performance is quite comparable in many regards. The three screens performed quite similarly in these motion tests, although the Dell and HP models were more like when we had boosted the Asus Trace Free setting up to 60. In these images you can see that the Asus has a slightly more pronounced motion blur than the other two, but it is free (at TF40) from the slight dark overshoot you see on the HP ZR2440w, and the more noticeable dark trails you can clearly see on the Dell U2412M.

 


24"WS 6ms G3G LG.Display e-IPS (Trace Free = 40)


24" 6ms G2G LG.Display AH-IPS


24" 4ms G2G AU Optronics AMVA (AMA = Premium)


24" 6ms G2G AU Optronics AMVA

We've also provided a comparison against three other 24" models we've tested. Like the PA248Q, the Dell U2413 is aimed primarily at higher end users and colour critical work. The difference being that the Dell also features some other high end features like wide gamut backlighting, 10-bit colour depth support and hardware calibration. The Asus is a little faster when it comes to pixel responsiveness, showing less noticeable blur in practice. While it's not shown in the PixPerAn images here, the U2413 also suffers from some obvious overshoot problems with transitions from dark to light colours.

The BenQ GW2450HM and Dell S2440L are AMVA based screens, but two of the faster models we've tested with this technology (which is traditionally fairly slow). They both show low levels of motion blur to the moving image, but do have a noticeable dark overshoot trail.


24"WS 6ms G3G LG.Display e-IPS (Trace Free = 40)


27" 2ms G2G Chi Mei Innolux TN Film +144Hz (Trace Free = 60)


24" 2ms G2G AU Optronics TN Film + 120Hz (AMA = On)


27" 1ms G2G Chi Mei Innolux TN Film + 120Hz (Over Drive = 0)


22" 3ms G2G Samsung TN Film + 120Hz

We've also included a comparison above against four very fast 120Hz+ compatible screens we have tested. In all cases these other screens are using TN Film panels and are aimed primarily at gamers. Firstly there is a comparison against the Asus VG278HE with its 144Hz refresh rate. This showed very fast pixel response times and smooth movement thanks to its increased refresh rate. You are able to reduce the perceived motion blur even more through the use of the LightBoost strobe backlight which we talked about in depth in our article about Motion Blur Reduction Backlights.

Then there is a comparison against the BenQ XL2420T. This showed very low levels of motion blur, but some dark overshoot was introduced as a side-effect. The Iiyama G2773HS was very responsive and even has a quoted 1ms G2G response time. This showed very low levels of blur and had minimal issue with overshoot. The Samsung SM2233RZ performed very well in these tests and showed very low levels of motion blur also. When 120Hz mode was enabled the overdrive artefacts evident in 60Hz mode were almost completely eliminated, which is something we have seen with the BenQ XL2420T as well.

There is something else going on as well here which can't be picked out by the camera. All of these other TN Film models are running at 120Hz (or higher) refresh rates, which allows for improved 120fps+ frame rates and the support of 3D stereoscopic content as well. This can really help improve smoothness and the overall gaming experience so these screens still have the edge when it comes to fast gaming.


The responsiveness of the Asus PA248Q was pretty reasonable. It wasn't as fast as some other panels we've tested like the fast TN Film models of course, but for an IPS panel it was decent. The Trace Free option allows you to control the overdrive impulse to taste, although we did find TF40 gave a good balance between reasonable response times and low levels of overshoot. The screen had an 8.4ms average G2G response time recorded and a well balanced performance across different transitions, both from light to dark shades and visa versa. Some other IPS screens have given us slightly faster response times, but normally at the cost of a more pronounced and problematic overshoot. Those wanting to play fast FPS or competitive games may want to consider some of the more gamer-orientated 120Hz+ compatible displays out there. Even better still would be models equipped with LightBoost systems for optimum motion blur elimination.



Additional Gaming Features
 

Aspect Ratio Control - The screen offers three options for aspect ratio control. There is a 'full' option which will always fill the screen no matter what the source resolution and aspect ratio, stretching it in whatever way is necessary to fill the screen. There is then a useful '1:1' option which maintains the source aspect ratio and maps the pixels 1:1 to the screen output. It would have been useful to perhaps see an "aspect" option which maintains the aspect ratio of the source, but fills as much of the screen as possible to give you a bigger image. A dedicated 4:3 mode is available when you switch to a non-native resolution which isn't 16:10 or 16:9 aspect ratio, although there isn't a 5:4 mode available.


Preset Modes -
There is no specific preset mode for gaming and so you will have to set up one of the other modes to your liking. The two 'user' modes might be handy here. The DCR function doesn't do anything in practice which is a shame, as some people may like that for games.

 


Lag

We have written an in depth article about input lag and the various measurement techniques which are used to evaluate this aspect of a display. It's important to first of all understand the different methods available and also what this lag means to you as an end-user.

Input Lag vs. Display Lag vs. Signal Processing

To avoid confusion with different terminology we will refer to this section of our reviews as just "lag" from now on, as there are a few different aspects to consider, and different interpretations of the term "input lag". We will consider the following points here as much as possible. The overall "display lag" is the first, that being the delay between the image being shown on the TFT display and that being shown on a CRT. This is what many people will know as input lag and originally was the measure made to explain why the image is a little behind when using a CRT. The older stopwatch based methods were the common way to measure this in the past, but through advanced studies have been shown to be quite inaccurate. As a result, more advanced tools like SMTT provide a method to measure that delay between a TFT and CRT while removing the inaccuracies of older stopwatch methods.

In reality that lag / delay is caused by a combination of two things - the signal processing delay caused by the TFT electronics / scaler, and the response time of the pixels themselves. Most "input lag" measurements over the years have always been based on the overall display lag (signal processing + response time) and indeed the SMTT tool is based on this visual difference between a CRT and TFT and so measures the overall display lag. In practice the signal processing is the element which gives the feel of lag to the user, and the response time of course can impact blurring, and overall image quality in moving scenes. As people become more aware of lag as a possible issue, we are of course keen to try and understand the split between the two as much as possible to give a complete picture.

The signal processing element within that is quite hard to identify without extremely high end equipment and very complicated methods. In fact the studies by Thomas Thiemann which really kicked this whole thing off were based on equipment worth >100,1000 Euro, requiring extremely high bandwidths and very complicated methods to trigger the correct behaviour and accurately measure the signal processing on its own. Other techniques which are being used since are not conducted by Thomas (he is a freelance writer) or based on this equipment or technique, and may also be subject to other errors or inaccuracies based on our conversations with him since. It's very hard as a result to produce a technique which will measure just the signal processing on its own unfortunately. Many measurement techniques are also not explained and so it is important to try and get a picture from various sources if possible to make an informed judgement about a display overall.

For our tests we will continue to use the SMTT tool to measure the overall "display lag". From there we can use our oscilloscope system to measure the response time across a wide range of grey to grey (G2G) transitions as recorded in our response time tests. Since SMTT will not include the full response time within its measurements, after speaking with Thomas further about the situation we will subtract half of the average G2G response time from the total display lag. This should allow us to give a good estimation of how much of the overall lag is attributable to the signal processing element on its own.

 

Lag Classification


To help in this section we will also introduce a broader classification system for these results to help categorise each screen as one of the following levels:

  • Class 1) Less than 16ms / 1 frame lag - should be fine for gamers, even at high levels

  • Class 2) A lag of 16 - 32ms / One to two frames - moderate lag but should be fine for many gamers. Caution advised for serious gaming and FPS

  • Class 3) A lag of more than 32ms / more than 2 frames - Some noticeable lag in daily usage, not suitable for high end gaming

For the full reviews of the models compared here and the dates they were written (and when screens were approximately released to the market), please see our full reviews index.

(Measurements in ms)

Standard Mode

Total Display Lag (SMTT 2)

8.3

Pixel Response Time Element

4.2

Estimated Signal Processing Lag

4.1

Lag Classification

1

 Class 1


We have provided a comparison above against other models we have tested to give an indication between screens. Those shown with blue bars represent the total "display lag" as at the time of review we did not have access to an oscilloscope system to measure the response time element and provide an estimation of the signal processing. The screens tested more recently are split into two measurements which are based on our overall display lag tests (using SMTT) and half the average G2G response time, as measured by the oscilloscope. The response time is split from the overall display lag and shown on the graph as the green bar. From there, the signal processing (red bar) can be provided as a good estimation.

The Asus PA248Q showed an average total display lag of only 8.3ms during the initial tests. This lag was very low overall which was pleasing, equating to around half a frame. We measured half the average G2G response time as 4.2ms and so we can estimate that the signal processing is approximately 4.1ms. This is certainly a very low lag and should present no problems for gaming as a result.
 

For more information about the SMTT 2.0 tool, or to purchase a copy please visit:

http://smtt.thomasthiemann.com/index_en.html

 


Movies and Video

The following summarises the screens performance in video applications:

  • 24" screen size makes it a reasonable option for an all-in-one multimedia screen, but being quite a bit smaller than most modern LCD TV's of course. As far as desktop monitors go it is at the middle end nowadays.

  • 16:10 aspect ratio is less well suited to videos than a 16:9 format screen, leaving larger borders on DVD's and wide screen content at the top and bottom.

  • 1920 x 1200 resolution can support full 1080 HD resolution content.

  • Digital interfaces support HDCP for any encrypted and protected content

  • As well as DVI there are also VGA, DisplayPort and HDMI  available which may be useful for connecting external devices. HDMI is particularly useful given it is so widely used.

  • Cables provided in the box for everything except HDMI which is useful, although it would have been good to see HDMI included really.

  • AG coating may appear too grainy or 'dirty' to some users as it is of the older type. May be distracting to some users on lighter content, but probably not an issue with movies and dynamic images.

  • Wide brightness range adjustment possible from the display, including high maximum luminance of ~291 cd/m2 and a reasonable minimum luminance of ~85 cd/m2. This should afford you very good control for different lighting conditions although if you are watching movies in a very dark environment, the lower level adjustment might not be optimal.

  • Black depth and contrast ratio are very god for an IPS panel being measured at 856:1 after calibration. Shadow detail in darker scenes should not be lost even when watching a lot of dark content.

  • Dynamic contrast ratio available on this model but does nothing in practice unfortunately.

  • There is a specific 'Theater' preset available which appears overly blue and also crushes static contrast ratio a lot. Probably should be avoided.

  • Good pixel responsiveness which should be able to handle fast moving scenes in movies without issue. Probably best to stick with a Trace Free setting of 20 or 40 for optimum performance and to avoid any overshoot problems.

  • Wide viewing angles thanks to IPS panel technology meaning several people could view the screen at once comfortable and from a whole host of different angles.

  • Very good range of ergonomic adjustments available from the stand so should be easy to obtain a comfortable position for multiple users or if you want to sit further away from the screen for movie viewing.

  • No noticeable backlight leakage, and none from the edges which is good. This type of leakage may prove an issue when watching movies where black borders are present but it is not a problem here.

  • No integrated stereo speakers on this model although there is a headphone audio connection to output the sound if using HDMI or DisplayPort.

  • Reasonable range of hardware aspect ratio options with 'full', 1:1 and 4:3 available. At least the screen is able to maintain whatever the source aspect ratio is using the 1:1 option.

  • Picture in picture (PiP) and Picture By Picture (PbP) are available if needed.

  • For PAL sources, we have tested the screen and confirmed it will support the full native resolution of 1920 x 1200 at 50Hz refresh rate.
     


Conclusion

Overall the Asus PA248Q seemed to be a pretty good all-round screen. Asus have certainly done a good job of providing a decent range of options and extras. The stand offers a very nice range of adjustments, there are decent video connectivity options and the addition of USB 3.0 is a nice touch. A couple of things fail to deliver, including the dynamic contrast ratio (no real surprise), and the use of PWM for backlight dimming might be off-putting to some. The older style AG coating is also not to everyone's taste but many won't find it an issue.

From a performance point of view the IPS panel delivers the kind of all-round performance we've grown to expect from this technology. The W-LED backlighting unit provides a standard sRGB gamut which will suit most normal users, but Asus have tried to focus this model on its colour accuracy. Here it falls a little short we felt. The default setup is moderate, but there are some discrepancies with gamma and white point which aren't possible to correct through the OSD menu and would require a calibration device to sort out. The so-called factory calibration didn't really deliver anything better sadly, and for some reason the 'user' preset modes, where you have access to change the RGB channels, do not allow a decent colour calibration. Having said that, the wide viewing angles, decent image quality and high (for IPS) contrast ratio mean the screen can deliver a good picture quality. If you are able to calibrate the screen, either with your own device or with the bundled Spyder4 package if you bought the PA248QJ version of the screen, then you should be able to overcome those limitations with gamma, white point and colour accuracy anyway.

We were pleased with the response time performance overall, and the Trace Free setting allows you a good control of the overdrive impulse to find a setting you like. The very low lag was also a positive when it comes to gaming, and so again this screen can deliver some decent all-round performance, not just limited to colour work as Asus' webpage would seem to target it.

At a retail price of ~324 GBP (inc VAT) it is however quite a lot more expensive than the Dell U2412M (~209), but a little bit less than HP's ZR2440w (~370). Whether it offers enough extra over the Dell is debatable, but its at least another decent 24" standard gamut alternative. There aren't many 16:10 aspect IPS models in this size produced nowadays, so the Asus may well be popular along side Dell and HP's offerings.

 

Pros

Cons

Good range of stand adjustments and additional USB 3.0 ports

PWM used for backlight dimming

Low lag and pretty decent response times for gaming

Older style AG coating may be too grainy for some people

Good contrast ratio and black depth for an IPS panel

Factory calibration didn't offer much, and hard to correct default gamma and white point

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