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Introduction

Over the last several years AU Optronics, one of the largest manufacturers of LCD panels in the World, have invested in the development and expansion of their Advanced Multi-Domain Vertical Alignment (AMVA) technology. In late 2010 this included the move towards the ever-popular LED backlighting which offered energy saving and environmental benefits along with slim screen profiles. BenQ as a monitor manufacturer are part of the same group as AU Optronics and so have always had access to their latest panels and been at the forefront of any developments which they might make. In December 2010 we tested the first VA + LED monitor in the form of the BenQ EW2420. Since then, the use of AMVA panels with LED backlighting has become more mainstream, extending to other manufacturers and into other screen sizes (e.g. the recently tested Philips 273E3QHSB 27" screen).

BenQ have now decided to expand their use of AMVA + LED into their GW series of screens which is aimed at home and office users. The 24" GW2450HM which we have with us for testing uses the latest generation of AU Optronics' AMVA technology so it will be interesting to see what improvements and changes have been made since those first panels a couple of years ago. BenQ have also released GW series screens in 21.5" (GW2250) and 27" (GW2750) sizes as we discussed in our news article in April 2012.

The 24" GW2450 screen actually comes in 3 versions with the only differences being the connectivity options and speakers. The regular GW2450 has only D-sub and DVI connections. The GW2450M then adds 2x 2W integrated stereo speakers and associated headphone and line-in connections. Finally the GW2450HM also adds an HDMI connection. There is a similar pattern with the 21.5" model which is available in 3 flavours, but the 27" only has the GW2750HM edition.

BenQ's website states: "After launching the world's first VA LED monitor, BenQ - the world's leading LED monitor brand - is now taking the lead to introduce VA LED to our home & office offering: GW Series! Built with the dream combination of LED with VA panel, GW Series is bound to bring a whole new visual experience and enjoyment to you with truly authentic colors, deeper blacks, higher contrast and sharper details. Built to bring you the ultimate personal visual entertainment, the BenQ GW2450HM is certainly one of a kind! Featuring the ultra-high 5000:1 native contrast, 20M:1 dynamic contrast ratio, and true 8-bit panel performance with deep blacks and minimized light leakage, this VA LED monitor refreshes your view with truly fantastic colors and details. And, its HDMI connectivity leads the path to a whole new level of multimedia enjoyment."

Specifications and Features

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

The GW2450HM offers a decent range of connections for a lower end home and office range monitor. There are DVI-D, HDMI and D-sub interfaces available for video connections. The digital connections are all HDCP certified and it's great to see HDMI included for connection of popular external devices like games consoles and Blu-ray players. DisplayPort is missing from this model which is becoming increasingly popular though. All the provided interfaces can support the full 1920 x 1080 resolution of the panel. As already mentioned the GW2450HM model is the only one of the 3 variants with HDMI included. The other two are limited to D-sub and DVI-D only. The screen is packaged with the VGA cable but does not come with DVI or HDMI unfortunately. Presumably a cost cutting measure from BenQ there.

There aren't really any extra features provided here and the screen is even missing USB ports which can be found on many monitors nowadays. There are only 2x 2W integrated stereo speakers available. There are no further features here such as ambient light sensors, card readers etc.

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

OSD Menu

Above: view of OSD operational buttons and labels. Click for larger versions

The OSD is controlled by a set of 6 buttons located on the right hand edge of the screen and as shown in the above photo (left). The labels for these buttons are then located on the front edge of the screen on the right hand side (right hand picture). The bottom button is the power on/off switch and also has a small LED built into it. This glows green during normal operation and amber in standby. During normal use you can't really see this when viewing the screen from head on as it is tucked just out of the line of sight on the side.

The other 5 buttons control various aspects of the OSD menu. The 'auto' button gives you quick access to the auto configure feature for analogue inputs. 'Menu' obviously takes you into the main OSD menu which we will look at in a moment. There is quick access to the volume control from the third button down (upwards arrow label), and then quick access to the range of preset modes from the fourth button down (downwards arrow label). Lastly the 'enter' button gives you quick access to input selection.

I did find that the buttons were slightly higher up than the labels on the front would indicate which was odd. So I initially found myself pressing the wrong button when 'aiming' in the middle next to the label. From a line of sight directly in front of the screen you can't see these buttons so you are dependent on the labels to guide you. Seems like they are a little misaligned which is a bit of a pain sometimes.

The main OSD menu looks like the above and is split into 5 sections, distinguished by the tabs along the top. You can then see a range of options in each section in the lower blue section. Some of these you can actually drill into for a further level of settings. Pressing the up/down arrows navigates between the tabs (a little hard to get used to as you're moving left and right on the screen), and pressing enter brings you into that selection.

The first tab is the 'display' tab with a range of settings related to the use of the analogue VGA input. They are greyed out here since we are using DVI. Given most users would probably want to be using DVI or HDMI on this screen in today's market, I would have preferred to see this as a later tab, rather than the first section when you open up the OSD menu.

The second section is the 'picture' menu which has a lot of useful features. There are the normal options for brightness and contrast of course. There are 5 gamma mode settings available and then a 'color' menu which you can drill in to. Once in the 'color' sub-section there are controls over the colour temperature preset and the RGB channels as shown above. This section should allow you some decent control over the screens colour setup for calibration. In the 'picture' section of the menu there is an option for the 'AMA' control which allows you to control the level of overdrive being applied for gaming. We will test this a little later on in the review.

The third tab is the 'picture advanced' menu. There is access to the range of 'Senseye' preset modes available here. There are options for standard, movie, game, photo, sRGB and ECO available here. When entering some of these presets other options shown here like the dynamic contrast ratio become accessible also. The 'display mode' option gives you control over the hardware level aspect ratio control options as shown above.

The fourth section is the audio menu, allowing you to control the volume of the speakers (or headphones if you have them plugged in). The last section allows you to choose the screen input and control several aspects of the OSD itself.

The GW2450HM also has a hidden factory menu available which is shown above. You can access this by holding the 'menu' button while you power on the screen. Once turned on, pressing 'menu' again brings up this menu. This confirms the screen is using an AU Optronics M240HW02 V6 AMVA panel which is useful to know. Another useful option here is being able to turn the BenQ screen boot logo off, and also the resolution notice if you want. Use this section at your own risk!

All in all the OSD menu offered a good range of options and controls. It looked quite good as well and seemed to be a decent enough bit of software. Navigation was a little tricky sometimes and it didn't feel that intuitive. This was compounded by the misalignment of the operational buttons with the bezel labels too. The navigation was also a little slow and laggy I felt, but overall at least there was a lot you could control if you wanted to. Once set up you probably won't need to change the settings much anyway.

Power Consumption

In terms of power consumption the manufacturers spec states normal ('On mode') power usage of 27W. In standby the screen apparently uses <0.3W.

We tested this ourselves and found that out of the box the screen used 29.9W of power while at its default 100% brightness setting. After calibration, where we had adjusted the brightness control to 17% and therefore the backlight intensity, this was reduced to 17.4W. In standby the screen uses only 0.7W of power. We have plotted the results of these measurements on the graph below:

Panel and Backlighting

The BenQ GW2450HM (and regular GW2450 / GW2450M models) utilise an AU Optronics M240HW02 V6 AMVA panel which is capable of producing 16.7 million colours. This is achieved through a true 8-bits per sub-pixel. The GW2450 series use White-LED (W-LED) backlighting and so the colour space of this screen is approximately equal to the sRGB reference and is considered a 'standard gamut' backlight type. A wide gamut screen would need to be considered by those wanting to work outside of the sRGB colour space of course.

PWM Flicker Tests at Various Backlight Brightness Settings

100%                                                  50%                                                   0%

We tested the screen to establish the methods used to control backlight dimming. Our recent article talks in more details about a common method used for this which is called Pulse Width Modulation (PWM). A series of photos was taken using the method outlined in the article. These were taken at 100%, 50% and 0% brightness. This allows us to establish 1) whether PWM is being used to control the backlight, 2) the frequency at which this operates, and 3) whether a flicker may be introduced or potentially noticeable at certain settings.

A thin white line was shown on an all-black background and a photograph was taken at a slow shutter speed of 1/8 second as the camera was scanned left to right in front of the screen. This produces a series of white lines which can be used to identify the frequency of the PWM and how quickly the backlight is cycled on and off. 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. 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.

The BenQ GW2450HM showed a cycling frequency of ~240Hz (30 lines at 1/8 second shutter speed) in the initial tests shown here. A further test at an even slower shutter speed allowed us to more accurately record the cycling frequency at approximately 255Hz. At 100% brightness there should be no flicker evident as the backlight is not cycled on and off using PWM. At lower settings PWM is used and the duty cycle becomes progressively shorter. Given the relatively low frequency of the PWM cycling compared with some other displays (e.g. PWM of 350Hz+) and the use of LED backlighting, there is a chance that flicker may be evident to some users as you lower the brightness setting as a result. The frequency was a little higher than some other screens we have tested however which were ~180Hz.

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:

BenQ GW2450HM - Default Factory Settings

  

The out of the box performance of the GW2450HM was a little mixed. The screen felt very bright when set at its 100% brightness default which is very common for desktop monitors. Apart from that, the image appeared a little cool perhaps to the naked eye and there was a slight green tendency as well. If we refer first of all to the CIE diagram on the left it confirms that the monitors colour gamut (black triangle) very closely matches the sRGB colour space (orange triangle). It extends a little past the sRGB space in some shades in this 2D view of gamut but is a little short in others. The screen would be considered a standard gamut offering of course, thanks to its W-LED backlight unit.

Default gamma was recorded at 2.1 average, leaving it only 4% out from the target of 2.2. Gamma was a little closer in darker grey tones at ~2.16 but strayed further from the target gamma curve in lighter grey shades. Still, overall this was not a big deviance and a decent enough default setup. This was tested while the screen was in its default gamma 3 mode by the way. Colour temperature was a little too cool and was measured at 7089k, being 9% out from the target of 6500k. Note that we are using a Spectrophotometer to make these measurements which is not sensitive to the W-LED backlight as some colorimeter devices can be. When using a standard gamut colorimeter not designed to work with modern backlighting units like W-LED, there can be a typical deviance of 300 - 600k in the white point measurement which is why some sources may refer to a different white point in this test incorrectly.

Luminance was recorded at a very high 305.2 cd/m² which is too bright for comfortable office use and even a fair bit higher than the specified 250 cd/m² maximum brightness of the panel. You will definitely want to turn the brightness control down a lot to get a more comfortable setting for day to day use. Even at this very high luminance the screen returned a very low black point of 0.12 cd/m². This gave us a static contrast ratio of 2580:1. This was amazing of course, and a lot more than any modern TN Film, IPS or PLS panel could offer. However, given the specified 5000:1 contrast ratio and the fact that this was the latest generation of AMVA panel, we had hoped for higher.

Colour accuracy was mediocre at default factory settings with an average DeltaE (dE) of 3.4, ranging up to a maximum of 9.0. There seemed to be an imbalance in the greens as well. You will need to make some adjustments if you require higher levels of accuracy, but even if you don't a simple change in the brightness control will be necessary.

Testing Colour Temperatures and Gamma

We had access to controls over the gamma and colour temperature from within the OSD which was useful. We first of all tested the average gamma and deviance from a target of 2.2 in each of the five settings. The default is setting 3.

The gamma modes offered an average gamma ranging from 1.8 up to 2.7. Mode 3, which is the default, returned a gamma which was closest to the target of 2.2, and only 4% out. We will stick with that mode when we calibrate the screen shortly.

There are also options in the OSD menu for colour temperature when you drill into the 'color' section. Here they are described in words as opposed to being listed with a target temperature. They are designed to make the screen cooler or warmer at some undefined value. As a reminder we are using an i1 Pro spectrophotometer device here which can accurately read the colour temperature of the W-LED backlighting. We measured the colour temperature of the screen in each of the preset modes. All other settings were left at factory defaults (gamma was returned to mode 3 here) and no ICC profile was active. The results are recorded below:

As you can see, the normal setting had returned us a white point of 7089k. The bluish mode made the image cooler and colour temperature was now recorded at 10,325k. Reddish made the image warmer and was measured at 6344k. The 'user mode' allowed you to control the individual RGB levels if you wanted to, although here we left them at 100% each. This mode had a colour temperature of 6948k which was a bit closer to our target 6500k than the 'normal' mode had achieved. Switching to the 'user mode' would again help improve default setup before profiling through adjustments to the RGB channels.
 

Calibration Results

I wanted to calibrate and profile the screen to determine what was possible with optimum settings and profiling. I 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.

I first of all changed the screen into the 'user mode' color temperature setting. This would also allow us to control the RGB channels during the calibration process which affords us even more control over the hardware itself. This would allow us to obtain an optimum hardware starting point and setup before software level changes would be made at the graphics card level. This helps to ensure tonal values are retained as much as possible. Adjustments were made during the process to the brightness control and to the RGB channels as shown in the table above. After this I let the software carry out the LUT adjustments at a graphics card level and create an ICC profile. The screen does not feature a hardware LUT calibration option so other than the OSD alterations, the rest of the process is carried out at a graphics card level in profiling the screen.

The calibration was largely a great success. The 4% overall gamma discrepancy that we saw before in gamma mode 3 (2.1 average) had been almost completely corrected now to leave us with 0% deviance and an average gamma of 2.2. There was still some slight discrepancy with the gamma curve as you can see from the table above. White point was also corrected to 6460k, bringing it pretty close to the target within 1% deviance (correcting the 9% we saw by default). Luminance had been reduced to a more comfortable 121 cd/m² after the adjustment of the OSD brightness control to 16%. Black depth was still excellent at 0.05 cd/m² and this gave us a calibrated static contrast ratio of 2443:1. Colour accuracy was also improved very nicely with dE average now only 0.8 and maximum only 1.6. LaCie would consider colour fidelity to be excellent overall with only some slight discrepancies in some cases.

Testing the screen with various colour gradients showed smooth transitions with only some very slight gradation in darker tones being evident. At the very dark end this was slightly more apparent. There was also some very slight colour banding evident in the darker tones if you look very closely which has been introduced because of some of the corrections being made at a graphics card level. Gradients had been smoother and free from this slight banding at default settings but the calibration process had corrected gamma and other areas resulting in some tonal value loss. It's not something you'd notice in practice, but those working with a lot of gradients may need to consider it.

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.

I calibrated the screen again, but this time leaving it in its default 'normal' colour temperature mode. This did not give us access to the RGB channels so the only OSD change we were making was to the brightness control.

The calibration was again a success. The 4% overall gamma discrepancy that we saw before in gamma mode 3 (2.1 average) had been almost corrected now to leave us with 1% deviance, but still with an average gamma of 2.2. There was still some slight discrepancy with the gamma curve as you can see from the table above but it was actually closer to the 2.2 in the different grey shades than we'd seen from the 'user mode' calibration. White point was also corrected to 6532k, bringing it almost spot on to the target. Luminance had again been reduced to 120 cd/m² after the adjustment of the OSD brightness control to 22% in this mode. Black depth was still excellent at 0.05 cd/m² and this gave us a calibrated static contrast ratio of 2596:1 which was slightly higher than we'd achieved in the 'user mode' where we'd lowered some of the RGB levels. Colour accuracy was also improved very nicely compared with default settings with dE average now only 0.5 and maximum only 1.3. Again slightly better overall than the 'user mode'. LaCie would consider colour fidelity to be excellent overall with only some slight discrepancies in some cases.

Testing the screen with various colour gradients showed smooth transitions with only some very slight gradation in darker tones being evident. There was also some slight colour banding evident in the darker tones if you look very closely which has been introduced because of some of the corrections being made at a graphics card level. This was a little more noticeable than in the 'user mode', only because the profiling was responsible for more corrections when in the 'normal' mode than in the 'user mode' where you can control RGB levels as well. Again, it's not something you'd notice in practice, but those working with a lot of gradients may need to consider it.

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

I've provided a comparison above of the GW2450HM against some of the other screens we have tested in a similar size range. Out of the box average dE was 3.4 which was mediocre. Some improvements had been made to default colour accuracy since the older BenQ EW2420 model (4.8) which was good. It was on par with some popular IPS alternatives such as the Dell U2412M (3.2) and the AOC i2353Ph models (3.0) for instance. It was also comparable in this regard to the cPVA based NEC EX231Wp (3.0). It was however a little behind some other popular 23 - 24" models like the Dell U2312HM (2.2) and HP ZR2440w (2.0) for example.

Once calibrated the dE average was reduced to 0.8. This would be classified as excellent colour fidelity by LaCie still, but it was not quite as low as some of the other screens here which reached down to 0.2 - 0.4 average commonly. Purely based on this measurement there is not really any significant difference here though. It's important to understand that it's not all down to a single dE value measurement though when comparing the picture quality and setup of a screen, this is just provided for a quick comparison really.

Some of the professional range models from NEC are even more accurate still than the other screens shown here. Professional grade monitors like the NEC PA series and P241W also offer other high end features which separate them from some of these other models, including extended internal processing, 3D LUT's and hardware calibration. These comparisons are based on a small selection of tests, so it should be remembered that other factors do come into play when you start talking about professional use. For further information and tests of a high end professional grade screen with hardware LUT calibration, you may want to have a read of our NEC SpectraView Reference 271 review.

The calibrated black depth and contrast ratio of the BenQ GW2450HM were excellent, with a very impressive static contrast ratio of 2443:1. This was a long way ahead than any modern TN Film, PLS or IPS panel could offer which only really reach up to around 1000:1 in the best examples. We had actually been hoping for more to be honest though since we had seen static contrast ratios of ~3000:1 from previous AMVA + W-LED tests, including the original BenQ EW2420W (2995:1), and also from a couple of cPVA + W-LED alternatives (NEC EX231Wp and Samsung F2380). This screen has a specified 5000:1 static contrast ratio and is using the latest generation of AMVA panel. We had hoped that the contrast ratio might have reached up to closer to this figure really, but the 2443:1 calibrated spec is still very good.
 

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.

Contrast Stability

The luminance range of the screen was wide with an overall adjustment range of 207.7 cd/m². At the top end, the 100% brightness control returned us a luminance of 301.2 cd/m² which was even higher than the specified maximum brightness of the screen which was 250 cd/m². The OSD menu brightness control allowed you to adjust this all the way down to 93.5 cd/m² which should afford you a decent enough range of settings for most users. For those wanting to work in very dark conditions it might not quite have the low level adjustment range desired but it was pretty decent. A setting of around 15% in the brightness control should return you a comfortable luminance of around 120 cd/m².

Black depth was very good across the range thanks to the modern AMVA panel. This ranged from 0.12 down to 0.04 cd/m².

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 in a linear relationship.

Static contrast ratio remained very high and stable across the range, with an average figure of 2634:1 which was impressive. It was much higher than any IPS, PLS or TN Film panel can offer and was certainly a strength of these new AMVA + W-LED panels. We have provided a graph showing the stability of that contrast ratio across the range of brightness adjustments. The small deviations may possibly be down to rounding errors though given how high the CR is, but we've included it for reference anyway.

Dynamic Contrast

The BenQ GW2450HM features a dynamic contrast ratio (DCR) control, which boasts a spec of 20,000,000:1 (20 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 I would use the 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 function was available when in either the movie, photo or game preset modes. You can then turn this feature from a setting of 0 (off) up to 5, which determines the strength of the feature. We tested the screen in the movie preset at the maximum setting of 5. When enabled, you cannot manually change the brightness or contrast controls any more.

Unlike a lot of screens we have tested recently, this DCR did seem to function very well. There was a fairly gradual and subtle change in the backlight intensity which took around 10 seconds in total to change from one extreme to the other, when switching between the white and black backgrounds. Transitions were pretty smooth as well which was good. At the brightest setting the screen reached pretty much as high as it's maximum backlight intensity with a luminance of 291.8 cd/m² being reached. This was then adjusted by the DCR down to a very low setting where the black depth actually went beyond the lower limit of 0.04 cd/m² we had seen before in our contrast stability tests, and down below 0.02 cd/m². This was the lower limit of the X-rite i1 Display 2 colorimeter so we were unable to accurately measure the minimum black point. This means that the DCR reached over 14,590:1 in practice which was very good.

We did test the screen with a completely all black image and confirmed the backlight was not being turned off completely. The black point was trending towards 0.0 cd/m² though so the DCR figure was impressive. We would like to start seeing realistic DCR figures being quoted from manufacturer, not made up numbers which don't translate into real performance. I'd rather see a screen like this with a useable DCR of 14,590:1 and above, than  a screen with an advertised 100 million:1 which only works in the most extreme and unrealistic circumstances that a user will never see. Good to see BenQ have provided a working DCR with an impressive adjustment range.

Viewing Angles

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

Viewing angles of the GW2450HM were characteristic of an AMVA panel. Horizontally they were reasonably wide although there was a contrast shift from an angle of >40� either side which made the image go pale and yellow quite noticeably. From a wider angle still the image had a more pronounced white tinge to it and you can pick this out from the images above. Vertically they were a bit more restrictive still with a fairly noticeable contrast shift detectable with even a slight movement up or down, and a pale tinge to the image being more obvious. This was also a little yellow from a wider angle, and this is brought out in the photos above. However, the viewing angles were certainly better than TN Film matrices in these regards, and free of the obvious vertical darkening you see from TN Film technology. However, they were not as wide as IPS or PLS matrices and the contrast shifts were more noticeable unfortunately.

There was also a pretty obvious off-centre contrast shift which is inherent to VA panel types. Using a test image which shows a dark grey font on a black background you can easily test this 'feature'. From head on, the text was invisible and largely lost within the black background. This is down to the pixel alignment in a VA matrix. As you move away from a central line of sight the text becomes lighter and is more easily visible, especially from an angle of about 45�. This is an extreme case of course as this is a very dark grey tone we are testing with. Lighter greys and other colours will appear a little darker from head on than they will from a side angle, but you may well find you lose some detail as a result. This can be particularly problematic in dark images and where grey tone is important. It is this issue that has led to many graphics professionals and colour enthusiasts choosing IPS panels instead, and the manufacturers have been quick to incorporate this alternative panel technology in their screens. I would like to make a point that for many people this won't be an issue at all, and many may not even notice it. Remember, many people are perfectly happy with their TN Film panels and other VA based screens. Just something to be wary of if you are affected by this issue or are doing colour critical work.

Above: View of an all black screen from the side. Click for larger version

On a black image there is a slight pale and purple tint introduced to the image when viewed from a wide angle. This isn't too severe and shouldn't present any real problems in practice.

Panel Uniformity

Measurements of the screens luminance were taken at 35 points across the panel on a pure white background. The measurements were taken using BasICColor's calibration software package, combined with the NEC customised X-rite i1 Display 2 colorimeter. The above uniformity diagram shows the difference, as a percentage, between the luminance recorded at each point on the screen, as compared with the reference point of a calibrated 120 cd/m² in the centre of the screen. This is the desired level of luminance for an LCD screen in normal lighting conditions, and  the below shows the variance in the luminance across the screen compared with this 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 GW2450HM was on the whole pretty reasonable. There did seem to be a difference overall between the top and bottom areas of the screen, with the top half being darker than the bottom. Around 80% of the screen was within 10% deviance of the target 120 cd/m² which was good. The maximum deviance was in the top corners, particularly in the top right where luminance dropped down to 97 cd/m² in the worst case (-22% deviance). All in all though there was nothing too severe here.

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 noticeable backlight leakage or bleeding from this sample which was excellent. Blacks were deep and very dark. There was some very very slight clouding from the bottom corners but this was hardly noticeable at all. This is positive news for anyone wanting to watch movies or play games as there's a good chance people will want to use the screen in darkened room conditions, and any leakage could have been very obvious and distracting.

General and Office Applications

The BenQ GW2450HM offers a pretty decent solution for general office and internet applications. The 1920 x 1080 resolution and 24" screen size offer a good screen real estate to work with, and side by side splitting of the screen is perfectly useable. The slightly reduced vertical resolution (1080 pixels) compared with a 16:10 format screen (1200 pixels vertically) means you do lose a bit of height however. I personally prefer a 1920 x 1200 screen for office work for this reason.

The 0.276 mm pixel pitch offers a comfortable text size for day to day use, a little bigger than some of the modern ultra-high resolution models like the 2560 x 1440 res 27" models for instance. Default luminance of the screen was recorded at 305 cd/m² which is too high for prolonged office use. You will want to turn the screen down probably to around 15% 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 93 cd/m² minimum.

There are no specific 'text' or 'internet' presets available from the OSD menu, so you will probably want to calibrate the standard or sRGB modes to a lower luminance at the very least. The rest of the default setup in terms of gamma and white point is pretty good as well so you should have a reasonable screen to work with, even if you don't have access to a calibration tool or means to accurately profile the screen. The pretty wide viewing angles of the AMVA panel mean you don't have to worry too much about obvious contrast and colour shifts during regular use, although you do need to be aware of the off-centre contrast shift if working with colour critical applications or dark content specifically.

I tested the screen using both the analogue D-sub and digital DVI interfaces. The DVI offered a slightly sharper image and better picture quality. I would recommend using the digital interface wherever possible. The light AG coating of the panel means you do not have to put up with the grainy appearance of some popular IPS based screens. This is particularly beneficial in office use where there are a lot of white backgrounds.

The screen sadly does not offer any USB ports which I think are always handy for connecting external devices. There are also very limited ergonomic adjustments available from the stand with only a tilt function provided. This does allow a reasonable adjustment range back and forth, but height adjustment is certainly missed. There are no added functions such as ambient light sensors or human motion sensors here, but BenQ have included 2x 2W stereo speakers which should be ok for some casual 'office noises' and the odd mp3 or YouTube video.

 
Above: photo of text at 1920 x 1080 (top) and 1600 x 900 (bottom)

The screen is designed to run at its native resolution of 1920 x 1080 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 1600 x 900 resolution while maintaining the same aspect ratio (16:9) to see how the screen handles the interpolation of the resolution. At native resolution the text was very sharp as you can see from the top photograph. When you switch to a lower resolution the text is more blurry. There was fairly low levels of overlap of the pixels and text was still reasonably readable, but of course quite a bit bigger. Native resolution is recommended where possible of course.

Responsiveness and Gaming

The BenQ GW2450HM  is rated by BenQ as having a 4ms 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 AU Optronics M240HW02 V6 AMVA panel being used is rated by AU Optronics with a 12ms ISO response time (black > white > black) for reference. A figure of 4ms G2G is pretty adventurous given some of the poor performance we've seen from AMVA panels in recent months, let's see if BenQ have really improved responsiveness or not.

Before we get in to the get into the side by side screen comparisons I want to quickly talk about the overdrive control available through the screens OSD menu. It is available within the 'picture' section under the 'AMA' (Advanced Motion Accelerator) option as shown above. This allows you to manually control the overdrive / RTC impulse being applied to the pixels, with settings of off, high and premium available. Overdrive is designed to help improve pixel responsiveness and reduce motion blur and ghosting in practice by speeding up the transitions the pixels make to change from one colour to another. You may wish to read our specs section for some further information about overdrive / response time compensation.

The screen was tested using the chase test in PixPerAn, a good bit of software for trying to quantify differences in real terms responsiveness between monitors. As a reminder, a series of pictures are taken on the highest shutter speed and compared. The images above are the best case examples from the screen with the AMA function off and then set to high and premium.

When AMA was off there was a pronounced blur to the moving image and something we had been accustomed to seeing from AMVA panels for some time now. The blur was at a similar level to the older BenQ EW2420 in fact when that had its AMA function enabled. We had never been very impressed by the responsiveness of these AMVA panels and with the overdrive control turned off there was no real change there. However, when you switch to the 'high' setting there was a noticeable difference in performance. Suddenly the moving car became much sharper and the motion blur and ghosting was reduced dramatically. Finally there seemed to be an overdrive control which worked well to improve the responsiveness of the panel! There was still some slight blur evident but it was much better than AMA off, and much better than we'd seen from other AMVA panels in the past. Turning the overdrive control up one more notch to 'premium' helped a little more. Blur was reduced again nicely and the movement was a little sharper than before. You could pick out a very small amount of overdrive overshoot on the image in the form of a dark trail behind the moving car. This was pretty minimal though and not something which should be obtrusive day to day. Overshoot is a result of an aggressive overdrive impulse which is not controlled correctly. On some models the overshoot can be severe and very obvious, but here it was not too bad. I would recommend running the GW2450HM in the 'premium' mode for gaming and fast action content.

Display Comparisons

The screen was tested again using the chase test in PixPerAn for the display comparisons. As a reminder, a series of pictures are taken on the highest shutter speed and compared, with the best case example shown on the left, and worst case example on the right. This should only be used as a rough guide to comparative responsiveness but is handy for a direct comparison of the impact of this setting:

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

24" 8ms G2G AU Optronics AMVA (AMA setting = On)

27" 6ms G2G AU Optronics AMVA (SmartResponse = Fastest)

27" 8ms G2G AU Optronics AMVA (AMA setting = Premium)

We have first of all provided above a comparison of the responsiveness of the GW2450HM against the three other AMVA panels we have tested in recent times. As you can see there is a pronounced difference between the new GW2450HM and all of the older models in these tests. All of the other models showed high levels of motion blur, even when their overdrive controls were turned up to the highest setting. This had led us to conclude in those reviews that this panel technology was, at the time of testing, unsuitable for any fast paced gaming. It had lagged a considerable way behind other panel technologies including the ever-popular IPS from LG.Display. Thankfully AU Optronics and BenQ have made some big improvements with the latest generation of panel, combined with their latest overdrive control in the GW2450HM.

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

24" 8ms G2G LG.Display e-IPS

24" 6ms G2G LG.Display H-IPS

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

I have provided a comparison of the GW2450HM above against some popular 24" models based on IPS panels. These other models are all modern overdriven panels, boasting response times of 6 - 8ms G2G. The AMVA panel of the GW2450HM was finally able to compete with these fast IPS screens which was great to see. In fact it offered fairly comparable levels of performance in these tests to the Dell U2412M and HP ZR2440w which had shown very low motion blur but a slight dark trail caused by the overshoot of the overdrive impulse. A good sign though for AMVA panels!

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

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

22" 3ms G2G Samsung TN Film + 120Hz

I've also included a comparison above against two very fast 120Hz compatible screens we have tested. In both cases these other screens are also using TN Film panels and are aimed primarily at gamers. Firstly there is a direct comparison against BenQ's own XL2420T. This showed very low levels of motion blur, but again some dark overshoot was introduced as a side-effect. The Samsung SM2233RZ performed very well in these tests and showed very low levels of motion blur. When 120Hz mode was enabled the overdrive artefacts evident in 60Hz mode were almost completely eliminated, which is something we have seen here with the BenQ XL2420T as well. There is something else going on here though as well which can't be picked out by the camera. Both of these TN Film models are running at 120Hz 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. From a pixel response point of view the GW2450HM had impressed here but there are some other areas you still need to think about when it comes to high end gaming.

The GW2450HM should be perfectly capable of even some fast FPS type games if you want and there had been some significant improvements made in this panel technology thankfully since the other generations we have tested. It is finally at a similar level to competing IPS models which is great news.
 

Additional Gaming Features

Aspect Ratio Control - The screen offers two options for hardware level aspect ratio control. There are settings for 'full' and 'aspect' here. The 'full' option will stretch the input resolution to fill the screen, no matter what that input resolution is. So this would stretch and distort the aspect ratio if the input is anything other than the native 16:9 aspect of the panel. The 'aspect' option however will stretch the input source to fill as much of the screen as possible, while still managing to maintain the same aspect ratio as the input resolution. If necessary it will then add black bars along the top or sides. There is no option for the screen to support 1:1 pixel mapping however unfortunately.

Preset Modes - There is a 'game' preset mode available from within the 'Senseye' preset mode menu if you want a mode with boosted brightness and a more unnatural feel. It also seems to over exaggerate the sharpness of the image. The dynamic contrast option is available in all this mode as well and we have already established that this works well on this model.

Input Lag

We have recently written an in depth article about input lag and the various measurement techniques which are used to evaluate this aspect of a display. We have also improved our method by adopting the SMTT 2.0 tool which is used to generate the results below. Please see our full input lag testing article for all the details.

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.

Our tests here are based on the new format using SMTT 2.0. We have provided a comparison above against other models we have tested to give an indication between screens. However, please note that many of the other screens tested here were using older stopwatch methods and not the SMTT 2.0 tool. For reference, those shown as darker blue lines were tested using SMTT 2.0.

The BenQ GW2450HM showed an average display input lag of only 6ms during this test, ranging up to 7ms maximum. This was very good and should not present any problems at all, even for fast gaming. The lag of this screen has been categorised as CLASS 1 as detailed above.
 

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, although quite a bit smaller than modern LCD TV's of course

• 16:9 aspect ratio is more well suited to videos than a 16:10 format screen, leaving smaller borders on DVD's and wide screen content.

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

• Digital interfaces DVI and HDMI support HDCP for any encrypted and protected content

• Good to see HDMI provided along side DVI as it's very useful for external Blu-ray / DVD player connectivity. Sadly DisplayPort is missing which is becoming increasingly popular. Might have also been good to see an HDMI cable provided in the box, but we can understand why it's been left out from a cost perspective.

• Black depth and contrast ratio are excellent thanks to the AMVA panel. Detail in darker scenes and shadow detail should not be lost due to these measurements.

• Dynamic contrast ratio is available and works very well, offering DCR's of over 14,500:1.

• 'Movie' preset mode is available which seems to accentuate the sharpness and colours and make everything look more vivid. Might be useful to some users

• Very good pixel responsiveness which should be able to handle fast moving scenes in movies without issue. A great improvement in this area with the latest AMVA panel generation.

• Pretty wide viewing angles thanks to AMVA panel technology meaning several people could view the screen at once comfortable and from a whole host of different angles. Not quite as wide as some other technologies such as IPS, and the off-centre contrast shift can be a little annoying depending on your line of sight.

• Limited ergonomic adjustment range available from the stand with only tilt available. It could prove difficult to obtain a comfortable position if you are watching from various locations and angles. Height adjustment would have been useful.

• No significantly 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.

• 2x 2W integrated stereo speakers available if you want, along with audio pass-through and a headphone socket. Might be useful for the occasional video but of course the speakers aren't up to a great deal.

• No picture in picture (PiP) or picture by picture (PbP) modes available on this model.

• For PAL sources, we have tested the screen and confirmed it will support the full native resolution of 1920 x 1080 at 50Hz refresh rate.

Conclusion

The BenQ GW2450HM was a very pleasing improvement to some of the other AMVA based screens we've tested over the last year or so, including the older BenQ EW2420, BenQ EW2730V and more recently the Philips 273E3QHSB. We'd always been impressed by the low cost of these models which made for an interesting alternative to the wide range of cheap TN Film screens flooding the market. However, each time we'd been quite disappointed by the poor pixel response times and this was an obvious limitation with these modern AMVA panels. Thankfully that seems to have changed and the latest generation of panel used here in the GW2450HM was much better. Finally pixel response times were at a level allowing this screen to compete with the popular IPS alternatives out there.

We continue to be impressed as well by the very high static contrast ratios of AMVA technology, although we are still to see a panel which achieves as high as the 5000:1 spec we're starting to see advertised. A calibrated figure of ~2500:1 is not to be sniffed at of course so it's still excellent and continues to be a strong point of VA matrices. This model even had a working and usable dynamic contrast ratio which is pretty rare for the desktop monitor market.

We did feel that the screen was a little lacking in some areas though. There were limited adjustments available from the stand but we can understand why these have been left off to keep costs down. AMVA panels are not great from a viewing angle perspective and do fall behind IPS in this area. They are better than TN Film though and really this seems to be one of the only weaker areas it seems of modern AMVA panels.

The GW2450HM retails for an amazing price of ~�140 GBP. This actually makes it cheaper than many TN Film based models in the market at the moment which tend to be ~�150 in many cases. It's also a lot cheaper than some popular IPS screens like the Dell U2412M (�230) and Dell U2410 (�360) for example. Obviously the features and extras vary a lot, but at a price of ~�140 this is a very compelling option in the 24" sector. Those looking for a low cost screen for normal home or office use would be well advised to consider the GW2450HM I think.