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Introduction

AOC is a brand that many people might not be familiar with, so therefore a short introduction. AOC’s roots lie with Admiral, founded in Chicago in 1934 and one of the first and largest producers of colour televisions in the early era of that medium. In 1967 Admiral Overseas Corporation (AOC) was established in Taiwan, the first manufacturer of colour televisions for export. Later Admiral Overseas Corporation was renamed AOC International and marketing began directly under the AOC name. In 1988 AOC added computer monitors to their line-up. Nowadays they are market leader in various countries in Asia and South America, with strong market positions in various European countries as well. They are no longer part of Admiral, but are now a subsidiary of TPV Technology, the largest manufacturer of computer displays in the world (mainly as ODM for other companies).

The q2770Pqu is one of their higher end displays, targeted at (semi) professionals. Mainly people who need the desktop real estate offered by this 27” QHD display, like people in finance, analysts, programmers and CAD, but also people in the graphics industry and gamers. It offers a wide range of ergonomic adjustments, excellent viewing angles and it is very energy efficient.

This review is also available in Dutch at Tweakers.net

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Versions and regions

AOC International works with three main regions:

The Americas
EMEA
Asia-Pacific

Product carrying the same model number may vary from one region to the other. There are at least two versions of the q2770Pqu: one for EMEA and one for the Americas. The product manager was not completely sure whether the Asia-Pacific region used the same version as the Americas or a third version. One thing is for sure, the version tested is the EMEA version and that version is only used in the EMEA countries. The EMEA version is advertised as using Samsung Super PLS and the Americas version is simply advertised as IPS. It may very well be that the Americas version uses a different panel, although various manufacturers have labelled AU Optronics AHVA, Samsung PLS and similar technologies as IPS before.Test results and specifications in this review may not apply to your q2770Pqu if you live outside the EMEA region.
 

Testing methods
 

You may have noticed by now that this isn’t your typical TFT Central review. Up till now all reviews were written by Simon, but this is the first review here written by Kid Jansen who has been involved in the site with other articles and content in the past. The equipment used is very similar, for instance we both use the X-Rite i1Display Pro and i1Pro. But we use different software to read the measurement data from the hardware. Furthermore, Simon mostly uses analyses made by the software, whereas I usually work with the raw xyY data and do the analysis myself in Excel and/or Matlab. You will notice some differences in the layout and content of the review as a result, but we've tried to make it as familiar as possible for our readers. Hopefully you will appreciate the additional reviews here!

Equipment overview
 

Notes
 

All tests were performed full screen at the native 2560x1440@60Hz display mode with the display connected to the graphics card by DisplayPort, unless stated otherwise. For all non-calibrated tests all OSD settings were reset to factory defaults, with the exception of the setting being tested. Except for the uniformity test and the checkerboard contrast test all the measurements with the i1Display Pro and i1Pro were performed in the centre of the screen. For the sequential contrast test and gamma test the i1Display Pro was mounted on a tripod.

Comparable Displays

The q2770Pqu has a few strong competitors in its class, like the Dell U2713HM and the ASUS PB278Q. For a more accurate comparison of the alternatives we’ve also used the work of PRAD.de, because they tested all the selected alternatives. All the pros and cons are in comparison with the q2770Pqu.

Acer B276HUL

The B276HUL is built around some version of the LG Display LM270WQ1 IPS panel.

Pros

·         Higher contrast ratio

·         2x HDMI

·         DisplayPort-out for daisy chaining

Cons

·         Higher energy consumption

·         Very high display lag

·         No VGA connection

·         HDMI cable not supplied with display

ASUS PB278Q
 

The ASUS PB278Q is a display that is very similar to the q2770Pqu. It’s build around the Samsung LTM270DL02 PLS panel, which was also used in early production of the q2770Pqu and which is very similar to the LTM270DL06 panel. It features the same Mstar MST9687D controller. They also feature the same Factory OSD and use exactly the same method to get into it. The PB278Q has the same display- and audio connections as the q2770Pqu and they are placed in the same order. Furthermore, the PB278Q also has 2x 3W stereo speakers that can playback input signals from DP, HDMI and a 3.5 mm stereo input. It is very likely that the PB278Q is also produced by TPV Tech.

Most notable differences are the lack of a USB-hub on the PB278Q, the difference in OSD and OSD-controls and the use of PWM controlled backlight dimming (at 240 Hz) on the PB278Q. Like the specifications, the performance is very similar. Both have a fairly mediocre performance out of the box, but perform much better when calibrated. Because of the similarities in parts and performance, the most significant differences are the lower price tag and better warranty policy on the q2770Pqu.

BenQ BL2710PT
 

The BL2710PT is built around the AU Optronics M270DAN01.0 AHVA panel. The AHVA technology is basically to AU Optronics what PLS is to Samsung; it’s their take on “IPS”. Like the q2770Pqu and the ASUS PB278Q the BL2710PT also uses the Mstar MST9687D controller. According to BenQ the BL2710PT is the first monitor specifically tailored for CAD/CAM design, with specific CAD/CAM and Animation modes.

Pros

·         Scaler has 1:1 pixel mapping mode and simple aspect mode that maintains aspect ratio of source

·         5 gamma presets

·         BenQ Display Pilot allows you to predefine the Display Mode per program and partition desktop

·         Ambient Light sensor

·         Motion sensor for automatically turning off display when not in use

·         8-bit + FRC colour depth to simulate 10-bit colour depth per channel

·         On-screen labelling of OSD-controls

Cons

·         Higher power consumption

·         Low contrast ratio (especially in our review of the BL2710PT)

·         User mode for white balance (individual RGB-controls) not working properly

 

Dell UltraSharp U2713HM
 

Probably the biggest competitor of the q2770Pqu is the Dell UltraSharp U2713HM. It is build around the LG Display LM270WQ1-SLB2/-SLC1 AH-IPS panel. The AH-IPS panel technology performs very similar to Samsung’s PLS technology. A remarkable similarity between the LTM270DL06 panel in the q2770Pqu and the LM270WQ1-SLB2 panel in the U2713HM is that 5 out of the 6 CIE 1931 xy chromaticity coordinates of the primaries are identical, with only the Gy-coordinate spotting a difference. This is very uncommon, especially since these panels are from different manufacturers. It may very well be that Samsung and LG Display used the same LED’s and colour filters for these panels.

Pros

·         Factory calibrated sRGB mode with a colour deviation of ∆E₉₄ < 5

·         Separate Hue and Saturation adjustments in Movie and Game modes

·         On-screen labelling of OSD-controls

·         Display 5:4 resolutions in native aspect ratio

·         Slightly better panel uniformity

·         All four USB-ports are USB 3.0
 

Cons

·         No DisplayPort and HDMI-cables supplied with the screen

·         Slightly higher power consumption

·         Slightly higher price

·         No integrated speakers

Iiyama ProLite XB2776QS
 

The XB2776QS uses an LG Display AH-IPS panel.

Pros

·         Higher contrast ratio

·         Scaler has 1:1 pixel mapping mode and simple aspect mode that maintains aspect ratio of source

Cons

·         Mediocre performance after calibration

·         High minimum brightness of 126 cd/m²

·         Vertical viewing angles rather disappointing for AH-IPS panel

·         Brightness fixed at a very high 322 cd/m² in sRGB mode

·         PWM controlled backlight dimming at 240 Hz

·         No DisplayPort and HDMI-cables supplied with the screen

Iiyama ProLite XB2779QS
 

The XB2779QS uses a version of the LG Display LM270WQ1 AH-IPS panel. What makes this display unique in the list of alternatives is that it is the only display with a glare coating. All the other displays have an anti-glare coating. For some people this is a deal breaker, while others might see it as a clear advantage.

Pros

·         Higher contrast ratio

·         Much better uniformity

·         Apart from brightness excellent out of the box performance

·         Negligible display lag

·         Scaler has 1:1 pixel mapping mode and simple aspect mode that maintains aspect ratio of source

·         YC_BC_R support

Cons

·         Very high minimum brightness of 159 cd/m²

·         High power consumption (partially due to high minimum brightness)

·         Reflections with dark screen content

·         HDMI and VGA cables not included

·         PWM controlled backlight dimming, but at a very high frequency of 11.2 kHz (no visible flickering)

Philips Brilliance 272C4QPJKAB
 

The 272C4QPJKAB uses a Samsung PLS panel.               

Pros

·         2x HDMI

·         Scaler has 1:1 pixel mapping mode

Cons

·         Stand only provides tilt adjustment, the other three (height, swivel and pivot) are not available

·         Very poor out of the box performance

·         PWM controlled backlight dimming at 200 Hz

·         High power consumption

·         No VGA connection

·         Very high over-scan with video signal

 

Philips Brilliance 272P4QPJKEB
 

The 272P4QPJKEB uses a Samsung PLS panel.               

Pros

·         2x HDMI

·         Scaler has 1:1 pixel mapping mode

·         Motion sensor for automatically dimming of the display when not in use

·         Built-in webcam with microphone

·         DisplayPort-out for daisy chaining

Cons

·         Low contrast ratio

·         Mediocre calibrated performance

·         Very poor out of the box performance

·         PWM controlled backlight dimming at 200 Hz

·         High power consumption

·         No VGA connection

·         Very high over-scan with video signal

 

Specifications and Features

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

The feature set of the q2770Pqu is nothing too spectacular, but it does cover the basics very well. More exclusive features like ambient light sensor, motion sensor, hardware calibration and uniformity correction are not featured on this display. It does however have all the common display inputs: DisplayPort, DVI, HDMI and VGA. The first three of those support the native resolution of 2560x1440 pixels and the HDMI connection also supports MHL 2.0 (1920x1080). The VGA connection supports a maximum resolution of 1920x1080 by default, but you can get it to work at the native resolution as well. It’s also nice to see that the cables for all four display connections are provided in the box, as well the USB 3.0 cable for the built-in hub and a 3.5 mm mini-jack male-male audio cable.

The USB hub has four ports: 2x USB 3.0 and 2x USB 2.0. One of the USB 3.0 ports is a fast charge port. The USB 3.0 ports are located at the right hand side of the back section and relatively easily accessible. The USB 2.0 ports are located at the bottom of the back section and are somewhat hard to access. The q2770Pqu also has built-in stereo speakers of 2x 3W and a 3.5 mm stereo output. Audio input can be supplied by DisplayPort, HDMI or a 3.5 mm stereo input. The stand of the display features all the common ergonomic adjustments: swivel, tilt, pivot and height adjustment. The OSD can be set to 16 different languages and offers various white balance -, gamma - and overdrive settings.

There are two scaling modes available in the OSD: wide (16:9) and 4:3. For the majority of resolutions the (most) appropriate mode is selected by default. There are no settings available for resolutions with a 16:10 or a 5:4 aspect ratio, nor is there support for 1:1 pixel mapping. The actual behaviour of the scaler is slightly more complex though, as can be seen in the Display Modes section. Not really a feature of the display itself, but more of the product as a whole is the 3 year warranty with on-site exchange. It is also certified as an ISO9241-307 pixel fault class I display, which is the second best rating and the same as for instance the Eizo ColorEdge CG models have.

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

OSD Menu

Above: OSD control buttons

The OSD is controlled by four buttons on the underside of the bottom bezel.

The OSD works intuitively and has a logical categorization. It’s also more complete than most OSD’s, offering three gamma modes, four overdrive modes and an automatic off timer among the basic settings you’ll find in most OSD’s. The control buttons do their job, but they do not work as nicely as for instance the touch controls on the Dell UltraSharp display with automatic function labelling on screen. They really do require some time to get used to and even then you’ll find yourself pressing the wrong button every now and then.

Photographs of OSD

OSD –Luminance

OSD – Image Setup (only available on VGA)

OSD – Colour Setup

OSD – PictureBoost

OSD – OSD Setup

OSD – Extra

OSD – Exit

Factory OSD
 

The Factory OSD (also known as Service Menu) is a menu for the manufacturer to set up the display. As an end user there isn’t really a good reason for accessing the factory OSD, except maybe the panel on timer, since the q2770Pqu doesn’t support Active Power On Time over DDC/CI.

Factory OSD. Click for larger version
 

From left to right and top to bottom these settings/values have the following meaning:

Explanations

Auto Color: Gain / Offset
 

Gain and offset are curve adjustments, like gamma. In the simplest model the effect of each on the output is as follows:

Therefore, gain is a multiplicative modulation, offset an additive modulation and gamma a power modulation. The effect of gain is most prevalent in the highlights, offset in the shadows and gamma in the mid-tones.Because gain and offset are curve adjustments that can be set per channel, they affect both white balance and gamma of the output. The values in the Factory OSD for gain and offset are all 12 bit values (0-4095), which shows that the internal processing bit depth of the controller is 12 bits per channel (incoming signal from graphics card and panel are both 8 b/ch).

While these values can be adjusted and saved the effect seems to be locked. When you adjust any of them the word “Fail” appears next to “Auto Color”. Which is a shame for the real power users, because they could use some tweaking. AOC told us that the values for these settings are identical on every sample of this model. So there is no factory calibration.
 

RGB settings for white balance modes
 

These settings determine the white balance for the four white balance modes. The available range for each of these settings is 28 to 227. The reason for this range is unclear. Their value is not linked to the locked, but visible, RGB settings for each mode in the regular OSD: if you change one of the values in the Factory OSD the corresponding value in the regular OSD won’t change. But there is a relationship between their set value in the Factory OSD and the value displayed in the regular OSD:

This results in:

Like the gain and offset settings, these settings are identical on every sample of this model.
 

Spread spectrum
 

The LVDS spread spectrum clocking settings are used to reduce the EMI emission of the display, while at the same making it less susceptible to EMI emitted by other devices, by widening the bandwidth of the LVDS connection between the controller and the panel electronics. While this reduces the EMI emission at any one frequency, the total radiated energy remains the same. So while narrowband EMI sensitive devices may experience much less interference because of spread spectrum clocking, the situation for broadband EMI sensitive devices remains unchanged. The “Freq” parameter sets the amount of spreading. The standard clock specified for the LTM270DL06 panel is 60.38 MHz and the maximum without spread spectrum is 65.63 MHz. So with spread spectrum the clock would be for instance 60.38 ± 3 MHz. The “Amp” parameter can be used to reduce the amplitude of the signal, therefore reducing the total radiated power.

DFM
 

Turning this on activates the Design For Manufacture mode. In this mode the AOC-logo at power on will not be shown and the display will go into power safe mode more quickly. This setting is locked by default.

BurnIn
 

Turning this on activates the built-in burn-in mode of the display: when there is no input source connected the display will automatically alternate between completely black, white, red, green and blue screens every second.

Erase EEPROM
 

This function resets all OSD and Factory OSD settings to default. It does not actually erase any of the four EEPROM’s discussed at Electronics. It lets the controller read the back-up values for OSD and Factory OSD from the 24C32WP EEPROM and then write them back to the positions of the corresponding current values on that same EEPROM. Trying to use this function will result in the word “Fail” appearing next to Erase EEPROM. There is probably an additional sequence required to unlock the Gain / Offset, the DFM and the Erase EEPROM functions.

Power Consumption

In terms of power consumption the manufacturer lists 45.0W maximum usage, 18.0 "typical" usage and less than 0.5W in standby. We carried out our normal tests to establish its power consumption ourselves.

The EcoModes on the q2770Pqu were not all tested separately, because all they do is change the brightness setting. Therefore there is no difference with setting the brightness to the same value in the Standard mode.

The q2770Pqu is extremely energy efficient, using about 19 W on average when calibrated to 120 cd/m². This is actually less than what a Dell UltraSharp U2412M uses at that brightness and about the same as what a U2312HM uses. Not bad considering the q2770Pqu offers a 77.78% larger desktop area and a 37.35% larger display area. Even at the highest brightness setting it still only uses 38 W on average. The highest measured peak in power consumption was 48.5 W with the brightness on the highest setting, displaying a completely white screen, all USB-ports in use and the built-in speakers blasting at full volume (actually pushing them past clipping).

Apart from the q2770Pqu being energy efficient the results of this test also clearly show that the q2770Pqu does not have a power supply with power factor correction. This is usually the case with computer hardware with a power consumption of less than 75 W, as it is not mandatory for those. The result is that the power factor is quite low, because of a leading current caused by the smoothing capacitors in the power supply. The reason the power factor increases at higher brightness settings is that under higher loads the capacitor will have a higher duty cycle. But the low power factor is nothing to get too excited about as a consumer; your energy bill won’t be higher because of it.

energy consumption
 

energy consumption comparison graph

Operation

Activation time
 

Although not the most interesting field of performance, it might still be relevant to some, as it can be quite a nuisance if it takes the display very long to produce an image on screen when you turn it on. The switch on time is measured from the moment you press the power button on the display to the moment you get an image on screen. Going in stand-by is measured from the moment the screen turns black to the moment the LED in the power button turns orange, which is when the monitor actually enters the stand-by mode, as could be verified by the energy monitor the display is plugged in to. Getting out of stand-by is measured from the moment you move the mouse to moment you get an image on screen. All measurements are in seconds and were performed on native resolution and frequency: 2560x1440 @ 60 Hz.

The results show that it the q2770Pqu around 6 second to switch on. Not particularly fast, but not extremely slow either. How long it takes for the display to go in stand-by varies greatly from one input to the other, with VGA being almost twice as fast as HDMI.

Getting out of stand-by takes the display around 3 seconds, with the exception of DisplayPort. When the screen enters stand-by the connection between the graphics card and display is lost (probably to save power). With DisplayPort it had trouble re-establishing that connection and once you get an image on screen you’ll get a message that there was a link failure. Apparently this has to do with pin 20 being connected in the DisplayPort cable. To avoid this problem either use a cable with pin 20 not connected or turn the display off instead of using the stand-by mode.
 

Switching Input Interface
 

The time it takes to switch from one input to another has also been measured. DVI to VGA and vice versa have not been tested, because the graphics card has one DVI-D single link and one DVI-I dual link port, therefore a native output on both connections simultaneously was not possible.
 

Panel and Backlighting

Panel Part and Colour Depth

The AOC q2770Pqu utilises a Samsung LTM270DL06 PLS (Plane to Line Switching) panel which is capable of producing 16.78 million colours. This is achieved through a true 8-bit colour depth as opposed to Frame Rate Control (FRC) being needed.

The panel is confirmed when dismantling the screen as shown:

Display Electronics

To verify what panel was used in the q2770Pqu the bezels and rear case were removed. Because the display did not have any backlight on hours on arrival the glue of the foil tape connecting the electronics chassis to the panel assembly (top picture below) wasn’t heated yet and therefore the tape could easily be removed without tearing it. Because of this it took little effort to take a look at the display electronics.

panel assembly and display electronics chassis. Click for larger version

circuit boards from lefts to right: USB hub - power circuit - main circuit board

main circuit board

Once to the electronics were revealed all the connectors on the main circuit board could easily be identified, as well as most of the integrated circuits.

Connectors

Starting middle left in clockwise direction

·         OSD controls

·         USB

·         Power

·         LVDS Pair #1 and #2 to panel electronics

·         Power to panel electronics

·         Speakers

Integrated circuits

1.       GMT G1084-33

·         3.3V 5A Low-Dropout Linear Regulator

2.       SKhynix H5TQ1G63EFR

·         1Gb (128 MB) DDR3 RAM

·         64M x 16 configuration

·         Normal power consumption

·         DDR3-1600 11-11-11 clock speed and timings

·         Used by the controller for the frame/line buffer

3.       Texas Instruments TPA3113D2

·         6W/channel stereo class-D power amplifier

·         Drives the built-in speakers

4.       Anpec APW7089

·         4A 26V 380kHz Asynchronous Step-Down Converter

5.       Diodes Incorporated AS7805A

·         1A 3-Terminal Positive Voltage Regulator

6.       Atmel 24C32WP

·         32Kb 2-Wire Serial EEPROM

·         Used for:

o DP EDID

o Factory OSD current values

o Factory OSD factory defaults back-up

o Regular OSD current values

o Regular OSD factory defaults back-up

7.       Atmel 24C02WP

·         2Kb 2-Wire Serial EEPROM

·         Used for HDMI EDID

8.       Atmel 24C02WP

·         2Kb 2-Wire Serial EEPROM

·         Used for DVI-D EDID

9.       Atmel 24C02WP (the smaller one of the two IC’s in the top left corner on main PCB in the second photo above)

·         2Kb 2-Wire Serial EEPROM

·         Used for VGA EDID

Panel Electronics

block diagram of the panel electronics

panel electronics

LVDS Pair #1 and #2 from main circuit board, together with the timing controllers

power from main circuit board, together with the panel electronics power circuit

These IC’s probably are the Source Driver IC’s

EDID

The EDID (Extended Display Identification Data) is a piece of information that tells the graphics card what display modes it supports amongst some other specifications. The EDID varies slightly per input interface. The DisplayPort EDID is displayed below.

Screen Coating

The screen coating on the q2770Pqu is a light, semi-glossy anti-glare (AG) offering. It retains its anti-glare properties to avoid too many unwanted reflections of a full glossy coating, but does not produce an overly grainy or dirty image that some thicker AG coatings can. There were no cross-hatching patterns visible on the coating.

Backlight Type 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 detailed panel spec sheet for DL06 panel we know that the backlight offers a 79.6% NTSC, 100.0% sRGB and 79.2% Adobe RGB coverage. Anyone wanting to work with wider colour spaces would need to consider wide gamut CCFL screens, or the newer range of GB-r-LED displays available now. If you want to read more about colour spaces and gamut then please have a read of our detailed article.

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 other symptoms as a result of the flickering backlight caused by this technology. We used a camera method as described in that article. This allows us to identify:

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

If PWM is used for backlight dimming, the higher the 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. The other factor which can influence flicker is the amplitude of the PWM, measuring the difference in brightness output between the 'on' and 'off' states. Please remember that not every user would notice a flicker from a backlight using PWM, 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.

The AOC q2770Pqu uses a Direct Current (DC) method for backlight dimming and does not use PWM at all. It can therefore be classified as flicker free.

For an up to date list of all flicker-free (PWM free) monitors please see our Flicker Free Monitor Database.

Contrast Stability and Brightness

All measurements were performed five times and averaged for increased accuracy. The results show that the q2770Pqu fails to achieve the specified 1000:1 contrast ratio at all brightness settings. Still, the q2770Pqu performs well here, with an average contrast of 922.1 and a calibrated contrast ratio of 906.5. The average increase in brightness per brightness setting point was 2.076 cd/m² and the black point was 0.00226 cd/m².

Luminance range of white

As the graph above shows the relation between the measured brightness for white and the brightness setting is almost perfectly linear. Any deviations here might just as well be caused by the i1Display Pro. On average the slope of the graph is 2.076 cd/m² / brightness setting. The brightness of the backlight is regulated through a direct current method. The q2770Pqu does not use PWM at any brightness setting to reduce the brightness.

The q2770Pqu does not achieve the specified 300 cd/m² for white at the highest brightness setting, but this should not be a problem for anyone, because it is far higher than the recommended brightness for most applications. Depending on the ambient lighting conditions a brightness of 100-160 cd/m² is recommended, with 120 cd/m² being the most used.

Luminance range of black

Contrast stability

The graph above shows that the contrast ratio is very stable for all brightness settings, with the lowest contrast being only 1.085% lower than the highest.
 

Simultaneous contrast I: 4x4 ANSI checkerboard

The required checkerboard patterns were created in Photoshop CS5 Extended and displayed in FastPictureViewer Pro 1.9.
 

With simultaneous contrast measurements black and white are reproduced simultaneously in a certain pattern. The most common pattern is the ANSI 4x4 checkerboard, which starts with black in the top left corner. The contrast ratio is then determined by dividing the average brightness of the 8 white patches by the average brightness of the 8 black patches.

Simultaneous contrast measurements give a more realistic representation of the perceived contrast with actual content. After all, most people won’t spend their time behind a computer looking at a white or black screen.

The resulting contrast is lower than the sequential contrast at the same settings. The difference can be explained by the uniformity of the panel. The contrast hardly drops because of the simultaneous rendering of both black and white.

Calibrated

The same test was also performed after calibration of the display.
 

Simultaneous contrast II: 16x9 checkerboard
 

To get an even more accurate representation of the real life contrast a 16x9 checkerboard was measured. Due to the size of the i1Display Pro the corners could not be measured, therefore 70 white and 70 black patches were measured.
 

Like with the 4x4 checkerboard the lower contrast ratio is mostly caused by the uniformity of panel.

Default Performance and Setup

Default settings of the screen were as follows:

We went on to test the default setup of the screen in various areas as described in the following sections.

Support TFTCentral, buy the AOC q2770Pqu using our affiliate link

Colour Banding
 

To assess whether the q2770Pqu suffers from banding 19 gradients were examined in FastPictureViewer Pro 1.9. These were created in Photoshop CS5 Extended and saved as 16-bit uncompressed TIFF. The consequence of insufficient colour depth is colour banding:
 

Two colours that differ enough from one another to be perceived as two different colours when viewed side-by-side do not differ enough from one another to be reproduced by the display in question as two different colours.
 

Most banding we come across is the result of compression of the source, as is the case with JPEG with high compression. However, displays also cause banding themselves. By definition every display has colour banding, because the number of levels that makes up the gradient is at most equal to the horizontal resolution. To avoid any further banding the number of levels per channel has to higher than or equal to the horizontal resolution. Assuming an even number bit depth per channel that requires 12 bits per channel or higher for all common resolutions up to 4096 pixels wide.

That is however assuming that the gradient covers the full range of levels. A screen wide gradient that only covers a quarter of the range would require four times as many levels per channel. To avoid banding caused by colour depth altogether 16 bits per channel would suffice. With such high colour depth you could reproduce a perfectly fluent screen wide gradient on a cinema 8K (8192x4320) display that covers only one eighth of the range. Perceivable banding is mostly caused by differences in brightness across the gradient. There is only perceivable chromaticity banding with 6 bit colour depth. For chromaticity 8 bits per channel is more than enough for colour gamuts similar to the sRGB colour space. Even for the largest RGB colour spaces (with real primaries) 9 bits colour depth per channel would be more than enough, although that would be rounded up to 10, because odd numbers aren’t used for colour depth. Even when the colour depth does cause more banding than the resolution, gradients may still be perceived as fluent if the colour difference between two adjacent levels is smaller than our eyes can perceive.

To assess whether the q2770Pqu suffers from banding 19 gradients were examined. The first 7 gradients have constant chromaticity across the gradient and differ only in brightness. The other 12 gradients vary in both brightness and chromaticity from left to right.
 

The results show that the 8 bit colour depth is not enough to prevent brightness banding. All gradients that show banding have a high brightness difference from left to right. Differences in chromaticity actually make it harder to see any banding on this display, otherwise gradients 8 and 12 would also have shown banding (16 and 17 probably too). Altogether the display performs here as expected. Nearly all 8 bit displays show banding with gradients 1, 3, 5 and 7. With 8 bits per channel there are only 256 combinations, which means that with a full width gradient each level is at least 10 pixels (or 2.331 mm) wide on a 2560x1440 @ 27” display. With those gradients the colour difference of adjacent levels is large enough for our eyes to see.

With 6 bit colour depth more gradients would show banding and the gradients that already show banding with 8 bit colour depth would show far more conspicuous banding. With 10 bits colour depth there might not be any perceivable banding at all, but I’ve never tested a display with native 10 bit colour depth, so I couldn’t say. If a display shows more banding than expected based on the colour depth, it’s most likely caused by a faulty gamma response. A calibration would probably solve that.

Gamma

The gamma value determines the brightness of all grey levels between black and white based on the brightness of white. The reason for gamma encoding is that human contrast perception is proportionate to brightness: you can discriminate smaller differences in brightness at a lower brightness. It would for instance be hard to distinguish between 200 and 201 cd/m², but the difference between 1 and 2 cd/m² is easily perceivable. The absolute difference is the same, but the relative difference is 200 times greater. Since display work with fixed point encoding (integers) you would have a very low relative brightness resolution near black and very high near white with linear gamma (linear relation between grey levels and brightness).

Example with white 100 cd/m² and black 0 cd/m²

The difference between RGB0 and RGB1 is reduced by a factor 772 while the difference between RGB254 and RGB255 increases by a factor of 2.19, when γ=2.2 instead of γ=1.

The gamma response of the AOC q2770Pqu is tested for all three gamma settings available in the OSD (Gamma1, Gamma2 and Gamma3) and is also tested after calibration. To test the gamma response the brightness has been measured for 20 grey levels, from 5% to 100% in 5% increments. Most RGB colour spaces use a gamma of 2.2, which is also the native gamma of most display panels. Therefore a gamma of 2.2 will be used as a target value for all modes.
 

The gamma value is then obtained by

Example for 10% grey=1.53 cd/m² and white=263.46 cd/m²

The target brightness is obtained by

Example for 10% grey with γ=2.2 and white=263.46 cd/m²

Gamma1
 

The default gamma setting for the q2770Pqu is the Gamma1 mode. With an average measured gamma value of 2.29 it’s the closest to the 2.2 gamma value used by many colour spaces, which is also the native gamma of the LTM270DL06 panel used in this display.
 

The largest deviations in gamma value can be found on both ends of the scale, but especially near white. The largest relative deviations in brightness can be found at the dark end of the scale. The 5% grey level stands out from the rest in that it’s only measured grey level with a gamma value that’s lower than 2.2, therefore it’s also the only grey level with a measured brightness higher than the target brightness. This is often the case near black and has to do with the black point of the panel: the brightness of black isn’t 0 cd/m² and therefore grey levels near black have an offset as well. Adjusting this in the gamma curve would result in black crush.
 

Gamma2
 

The Gamma2 mode has a lower gamma, meaning that the brightness of the grey levels between black and white have a higher brightness. The average gamma value in this mode is 2.02, but the gamma value shows very large deviations. This mode might be useful to start from when a gamma value below 2.2 is required (for instance 1.8, used by some colour spaces), but it would definitely require a calibration.