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[Update 2] Testing ‘HDR400 True Black’ and ‘Peak 1000’ Mode Brightness on New OLED Monitors

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Originally published 14 March 2024, last updated 7 June 2024

Introduction

Since we published our video reviews of the 32″ MSI MPG 321URX and 27″ MPG 271QRX OLED monitors recently we’ve had some feedback on our YouTube comments, and via Reddit, about the brightness of the different HDR modes. The same feedback can be found online for the new 32″ Dell Alienware AW3225QF and the Asus ROG Swift PG32UCDM, and all these new screens seem to have the same thing in common – they have HDR settings in the menu for “True Black 400” and “Peak 1000” available and there seems to be visual differences between them both.

To investigate this, we wanted to carry out some further testing to see if we can establish what is going on and check some of the feedback we’d received. The performance of all three MSI models (27″, 32″ and 49″) was very similar in our reviews, and so we expect the same results from this testing to apply to all of their new models. There seems to be a common trend with other screens like the Dell and Asus models too, and so we expect the general overall findings here probably apply to all of these screens where there is a True Black 400 and Peak 1000 mode to choose from. We have fed back the findings in this article where possible to the product teams at MSI and Asus for further investigation as well and continue to consider how we can provide a more complete data set for future reviews and evaluation of monitor HDR performance.

Reminder of HDR peak luminance performance from our reviews

Here’s a quick summary of the peak white luminance performance measurements taken from two of our reviews as an example in HDR mode, with HDR test patterns generated by Portrait Display’s Calman Ultimate software. These test patterns simulate a white test area against a black background, which increases in APL area % (Average Picture Level) to simulate different HDR content. It’s a standard test that is useful for identifying HDR luminance capability.

MSI MPG 271QRX

You can see that both modes have very similar white luminance capabilities from these tests from 100% APL (full field white), down to 10% APL. For smaller APL from there, the True Black 400 mode (referred to from here as ‘TB400’ for ease) doesn’t get any brighter, and reaches it’s peak at around 471 nits maximum. The ‘Peak 1000’ mode (referred to from here as ‘P1000’) on the other can get brighter for the smaller APL of 5% and 1% areas measured, reaching up to 1002 nits maximum and therefore meeting the 1000 nits peak brightness spec of the panel.

Dell Alienware AW3225QF

The results from the Dell screen are very similar. The same tailing off happens in the TB400 mode where the luminance does not get any higher for the smallest APL, but the P1000 mode pushes up to over 1000 nits. Other than that, the HDR luminance remains basically the same for all other higher APL % measurements in these specific tests.

This trend of HDR luminance continues for the other models reviewed, including the 32″ MSI MPG 321URX, 49″ MSI MPG 491CQP,the 27″ Dell Alienware AW2725DF and the 32″ Asus ROG Swift PG32UCDM for example. In fact it seems to be common across loads of OLED monitors.

Testing both HDR modes in Windows desktop

This is where things start to get a little confusing. The feedback we’d received suggests that in Windows desktop:

  1. Visually the TB400 mode looks brighter than P1000 mode
  2. Testing the screen with a full-field white image is brighter in the TB400 mode
  3. You can see more noticeable ABL (Automatic Brightness Limiter) dimming when using the P1000 mode as you resize and move windows around

These observations are all true but remember that this is applicable when viewing SDR content (including Windows desktop) within the HDR mode. In our original investigation our first round of testing suggested that this only seemed to apply in this scenario although later testing has revealed some other issues with viewing actual HDR content which we will come on to in a moment. This scenario is likely to be one of the key situations that is leading to the observations and also to some confusion.

All 3 of the above observations are correct when enabling HDR mode in Windows desktop and when viewing any SDR content on the screen in that mode. The TB400 mode does look brighter as you switch between the two modes on Windows desktop, including for a full field white test pattern. You can also see much more ABL dimming as you resize and move windows in the P1000 mode in this scenario.

We took some simple measurements of white luminance again, but this time using SDR test patterns to simulate what is going on when you view Windows desktop and SDR content within the two HDR modes:

MSI MPG 271QRX

These two sets of measurements are taken with the Windows SDR brightness slider set at 40. You can see similar luminance is reached for the smaller APL measurements, but the luminance drops off much more drastically as APL increases when you’re using the P1000 mode. This is where you can see more noticeable dimming of real images in Windows desktop / SDR as the ABL feature is more aggressive.

At full-field white you can see that the luminance measured in TB400 mode is almost twice that of the P1000 mode (90 vs 171 nits). Remember though that this does not mean that we perceive it to be twice as bright, these are just luminance measurements (explained more in this article). In fact the perceived brightness difference calculated as an XCR score would be around 31% higher in the TB400 mode for full-field white.

We can see the same trend with SDR content viewed within HDR mode when bumping the Windows SDR brightness slider up to the maximum 100. Both reach similar luminance levels for small APL, but the drop off is again more drastic in the P1000 mode for SDR content. Full-field white is around 122 nits higher in the TB400 mode than P1000 mode, which is around 27% higher in perceived brightness.

This behaviour explains the observations about TB400 mode looking brighter in Windows and the more noticeable ABL dimming.

Dell Alienware AW3225QF

We can see the same trend on the Dell Alienware AW3225QF when measuring SDR content while running in HDR mode (Windows SDR brightness slider at 100 here). Again both screens reach a similar maximum luminance for the smallest APL, but the P1000 mode tails off much more quickly as APL % increases, and you get far more noticeable ABL dimming.

This suggests to us that this same behaviour will apply on probably all these new OLED monitors which feature a True Black 400 mode and a Peak 1000 mode. Remember though, at the moment we are talking about SDR content we are viewing while in HDR mode.

What is happening in SDR content?

With HDR mode enabled, both modes appear to be following the same ABL dimming behaviour when viewing SDR content, like the Windows desktop, as they do for proper HDR content. The difference is though that even at 100 brightness on the Windows slider, the screens only reach up to around 500 nits maximum, not the 1000 nits it can when displaying proper HDR content. If you compare the performance in the TB400 mode, you can see the luminance measurements are very similar between HDR content, and SDR content when the Windows brightness is set at the maximum 100%.

We’ve updated the vertical scale on the SDR graph to have the same scale as the HDR graph so it’s easier to compare the two:

MSI MPG 271QRX

While using the TB400 mode, both SDR and HDR content reach around 470 nits for the smallest APL, but drop off to around 275 nits for 100% full field white. The trend and shape of the luminance line on the graph is basically identical, so you can see that the behaviour of the ABL dimming is the same in TB400 mode regardless of whether the content being viewed is SDR or HDR. We’ve split the data out in to separate graphs below too:


If we compare the same for the P1000 mode, this is what causes the dimmer appearance when viewing SDR content. We’ve left the scales in these graphs as they were before, but you can see in this example the shape of the line is basically the same, but now the vertical axis scale is different:

The shape of the lines in P1000 mode is very similar, but the difference is that in SDR content the screen only reaches up to around 500 nits maximum, whereas in HDR mode it reaches twice that at 1000 nits. Both follow a similar ABL dimming profile and the luminance drops off in a similar way, but this means that by the time you reach 100% APL (full-field white), the luminance of the SDR content is a lot lower too. Had SDR mode actually started at ~1000 nits for the smallest APL ate the top left of the graph, it should have followed the same line pretty much for both SDR and HDR content.

So these measurements confirm the observations that TB400 mode looks brighter than P1000 mode in Windows desktop and when viewing SDR content, with a brighter full-field white (and other larger APL), and less aggressive dimming and ABL behaviour.

Auto HDR functions

We expect the above behaviour to apply for content that is “upscaled” from SDR to HDR using relevant “Auto HDR” functions.

Measuring HDR content

While the above observations are all true and valid, the missing part of this puzzle seems to be what happens when you view actual, real HDR content in these modes. The behaviour of TB400 and P1000 when viewing Windows desktop and SDR applications is interesting, but that’s not what these modes are designed for. As we covered in our article previously, Here’s Why You Should Only Enable HDR Mode on Your PC When You Are Viewing HDR Content. We would still recommend only enabling HDR when you are going to view HDR content ideally, especially in this case when you’re trying to choose the optimal HDR mode to use.

We’ve already taken peak luminance measurements using Calman Ultimate test patterns shown earlier in this article which show that the white luminance should be the same across the different APL’s, except for the smallest APL highlights where the P1000 mode can reach much brighter. Here’s a reminder of the comparison of those measurements from the Dell AW3225QF:

Important: For now, keep in mind that this represents measurement of an HDR white test pattern in both modes, which we provide as a comparison to the same SDR white test patterns we’d measured before. A bit later we will look at other measurements and uncover more information about HDR content performance in both modes.

Real world HDR content tests

To further test the two HDR modes in our original phase 1 version of this article, we also used a series of real-world tests to observe and measure real HDR content rather than relying only test patterns. To try and establish something that is repeatable and that you can replicate yourself if you own these screens, we’ve used a series of HDR YouTube videos for this real content testing, and each is linked below. HDR was enabled in Windows without any further setup using the Windows 11 HDR calibration tool.

We then simply switched between the two HDR modes on the monitor to view the videos. We paused them at various points to simulate different APL scenarios, from scenes with dark images and small highlights (low APL %) to overall brighter scenes with larger areas of brighter content (larger APL %). For good measure we also used a full-field white test pattern from the VESA DisplayHDR testing tool (downloadable for free from the Microsoft Store on Windows) in case there was any difference between that and the HDR test patterns from Calman (there wasn’t).

We took several screen measurements using our UPRTek MK550T spectroradiometer device which can be used as a hand-held, standalone device and can measure luminance by simply pointing the device at the screen in different areas and taking a measurement.

The MSI MPG 271QRX was used for these measurements, but the same behaviour should apply to the other OLED’s discussed in this article based on our earlier observations of behaviour.

We’ve provided screenshots from the video timestamps below for reference, but please note these are screenshots and not photos, and should not be used for testing or measurement. They are included to give you a quick visual reference of the scene measured and tested.

HDR Movies and Videos

MSI MPG 271QRXMeasured luminance (nits)
Test image detail, timestamp and link to videoScreenshot of measured imageTB400 ModeP1000 Mode
VESA DisplayHDR test tool – full field white image (100% APL)272270
Christmas Lights video – yellow lights highlight (1:13) – small APL %279669
Christmas Lights video – bright central lights highlight (1:28) – small APL %488852
Jazz video – light bulb central area (0:18) – small APL %339707
Jazz video – light next to player’s mouth (0:32) – small APL %459680
Jazz video – blue smoke area to the right of the DJ (1:54) – medium APL %270276
Jazz video – brighter, left side of speaker area (0:01) – medium APL %11290
Chasing the light video – sun rise measurement of sun (0:10) – medium APL %361367
Chasing the light video – sun over building (0:29) – medium APL %336339
Chasing the light video – white circular ceiling area (0:40) – medium APL %212171
Chasing the light video – light shining on ceiling (0:49) – medium APL %341364
Chasing the light video – sun in the sky in sunflower field (0:23) – medium APL %362369
Avatar trailer – sun in the sky (1:10) – low/medium APL %307425
Avatar trailer – sun above the water (1:16) – low/medium APL %291314

You can see from the measurements in these real content videos and movies that the P1000 mode was able to reach higher peak luminance than the TB400 mode for lower APL scenes and for bright highlights. The Christmas light videos were a very good example of low APL % scenes where the P1000 mode reached a lot higher luminance than TB400, and where you can experience the full brightness capability of the panel.

An example low APL % scene where the P1000 mode reached much higher luminance than TB400

Other scenes with a higher APL % showed very similar luminance between both modes, confirming our earlier measurements of white luminance. For instance the two sunrise “chasing the light” videos showed very similar luminance measurements for the bright sun area in each mode. In these situations, the APL was too high for the panel to push its maximum luminance, and with both modes offering a similar performance for medium/large APL (for HDR content), they produced a similar peak luminance.

An example of a medium APL % scene where both modes reached very similar luminance for the rising sun highlight

There were a couple of scenes where the TB400 mode reached a slightly higher luminance than the P1000 mode, those being the speakers scene and the circular ceiling shown below:

The luminance was a little higher on the speaker (112 vs 90 nits) and ceiling circle (212 vs 171 nits) but not by a huge amount. This looks to be caused by the more gradual roll-off of luminance in that mode. More on this in a moment.

During this initial phase 1 of our testing using these HDR videos the P1000 mode did seem to out-perform the TB400 mode when it comes to brightness, especially in situations where the APL is low and the scenes can reach the full brightness of the panel for small highlights. We will hold our hands up and say that these tests were not complete at the time, and there is more to this complicated issue that we will cover below.

[Key update 1] Here’s why TB400 can sometimes look brighter than P1000

How do we explain the continuing observation though from many users that some HDR content can look overall brighter in the TB400 mode than the P1000 mode? We’re not talking about the brightest highlights, which we’ve already shown to reach brighter peak in the P1000 mode, but the overall appearance of the rest of the scene. Why does the overall image appear brighter in many situations in the TB400 mode?

Our latest round of testing has uncovered the reason for this, and it’s to do with the PQ EOTF tracking and tone-mapping.

A quick background to PQ EOTF measurements

Greyscale input measurements used for PQ EOTF tracking from black (0) to white (100)

To try and explain this in simple terms, when HDR is measured you are basically measuring the luminance of various grey shade input signals from black (0) to white (100). We’ve provided a visual representation of those greyscale shades used in the measurements from Calman’s software. You can see that shades from 0 > 30 are dark grey, then around 50 – 60 you might consider mid grey, with anything above being considered light grey. White is at 100.

The measurements are plotted on a PQ EOTF graph like the one above and you can see the scale for the input signal along the horizontal X axis from 0 to 100. The yellow line represents the target/ideal PQ value that should be followed (PQ EOTF is akin to “gamma” in SDR), while the grey line, which is hard to see in this example as it follows the yellow line very closely here, tracks the actual monitor measurements. Ideally these lines should match and would show that the luminance of the grey shade being measured is accurate and as intended. If the monitor tracking line goes higher than the yellow line it means the luminance is higher than it should be, while if the line drops below the yellow line it means luminance is lower than it should be.

One other thing to note it that you will see that when the line reaches greyscale value 70 (light grey shade) the yellow target line flattens out completely which would mean that if this is followed exactly by the monitor, all those grey shades from 70 to 100 should actually have the same luminance, and would therefore look the same. Those lightest grey shades get clipped and lost and become white basically. This is how it’s defined in the HDR PQ standard but it is down to the display manufacturer to determine the “roll-off” point. Often you will see the luminance drop a little lower and more gradually level off rather than take such a sharp turn at greyscale 70. That can then help preserve lighter grey tonal values. This is especially useful in situations where the peak luminance of white is lower, like for instance on OLED screens where the APL % is high.

Think of it this way – for small 1% APL you might have a full luminance range of 0 – 1000 nits to play with on an OLED monitor, and so clipping light grey shades above greyscale 70 isn’t a major problem as they will be very bright at that point (nearing 1000 nits) and it’s going to be very hard to tell them apart anyway. For a large 100% APL the screen might only be able to reach perhaps 250 nits peak white and now you have a much smaller 0 – 250 nits range to play with. The display manufacturer might choose to clip the grey shades later on by rolling off the luminance more gradually since it’s going to be easier to tell the differences between those lighter grey shades when white is reaching only a much lower 250 nits peak.

Further measurements of the PQ EOTF tracking in both modes

Here’s some examples of the PQ EOTF curve and associated luminance graph (also useful for comparisons here) while running in the Peak 1000 mode. Click the tabs to cycle between the graphs for different APL.

Remember the APL (Average Picture Level) represents how much of the scene is bright. A 1% APL is a very dark image with just a small area of the screen being bright, like for instance car headlines at night. A 50% APL scene is a much brighter overall scene, and something like a 75%+ APL could represent for instance a snow scene where most of the scene is bright.

Note: For this further testing we were using the MSI MPG 491CQP (49” QD-OLED) but again these results should apply across the other recent OLED monitors featuring these modes – including especially the 27″ and 32″ models which are both very similar in performance as this 49” model.

Peak 1000 mode

1% APL
10% APL
25% APL
50% APL
75% APL
100% APL

You can see the problem here. The tracking of the PQ curve gets progressively worse as the APL of the image increases. For dark scenes with small bright highlights (e.g. 1% APL), and where the panel can reach up to 1000 nits the PQ tracking is very accurate and follows the target line nicely.

For the larger APL scenes, the source signal between around 45 and 80 falls well below the target line. This source signal range represents mid to light grey shades (and colours once those have been filtered) and with the grey line representing the monitors performance dropping below the target line, this means those mid to light grey shades are quite a lot darker than they should be. Ideally the PQ tracking should be consistent for all APL, so that all grey shades (and resulting colours) are at the correct luminance.

True Black 400 mode

1% APL
10% APL
25% APL
50% APL
75% APL
100% APL

In the True Black 400 mode you can see that the PQ EOTF tracking is far more consistent across the different APL’s. It’s not perfect and is still a bit darker than intended for the larger APLs, but it’s much better than the P1000 mode with a less drastic drop off. The measurement line from the monitor is much closer to the target yellow line, including for larger APL, even up to 100% full field white.

Comparing different greyscale input signal luminance

We can also take some specific luminance measurements using different greyscale input signals to further highlight this difference. Here’s the familiar graph which represents normal “peak luminance” measurements of both modes (again using the MSI MPG 491CQP for this section):

Using a normal white test pattern (signal input level = 100) you can see that both modes are the same for all APL between 10% and 100%, but the P1000 mode can reach higher peak luminance for the smaller APLs. This is in keeping with the earlier measurements of HDR content in the two modes.

PQ tracking in P1000 mode at 50% APL – red dots mark the point for the greyscale 100 (white) input signal

If you refer to the PQ tracking curves you can see that both the P1000 and TB400 modes follow the correct PQ tracking for this white input signal at all the different APL’s, marked with a red dot on the above example. This is why when measuring white HDR content and test patterns the P1000 mode is capable of the higher brightness, but should never look darker than the TB400 mode even at larger APL.

PQ tracking in P1000 mode at 50% APL – red dots mark the point for the greyscale 80 input signal

The same applies when you measure a light grey input signal (80). This is because the part of the PQ graph where the P1000 mode starts to deviate from its intended tracking lies between the input signals of around 45 and 80, representing mostly mid-grey shades.

PQ tracking in P1000 mode at 50% APL – red dots mark the point for the greyscale 70 input signal

When measuring a light grey (70) input signal the P1000 mode can reach a higher peak luminance for the smallest APL (below 10%) still, because if you remember back to the PQ tracking curves we provided earlier, the PQ tracking in this mode is still very good for the smaller APL.

However, you can see that for the larger APL the P1000 mode is now darker, and this is caused by that poor PQ tracking for the mid grey shades (signal levels 45 – 80) for the larger APLs. For instance at 50% APL the TB400 mode has a 112 nits higher luminance while at 100% APL the TB400 mode is 100 nits higher. This equates to around an 18 – 19% difference in perceived brightness (based on XCR)

PQ tracking in P1000 mode at 50% APL – red dots mark the point for the greyscale 60 input signal

For a mid grey input signal (60) both modes have the same luminance performance for the smallest APL, again because the PQ tracking was good in both modes in those situations. For the larger APL above 10% because the P1000 mode has inferior PQ tracking for these mid grey shades, the luminance drops off and is much lower.

PQ tracking in P1000 mode at 50% APL – red dots mark the point for the greyscale 40 and 20 input signals

For the darker grey shades the performance returns to being basically the same in both modes, and that’s because the PQ tracking is back to being accurate in both modes.


So to summarise the findings above:

  1. It is the larger APL above about 10% APL where the P1000 mode starts to deviate from the intended PQ tracking, quite significantly.
  2. The “problem area” is for input signals between around 45 and 80 as indicated on the example graphs below, and representing mid grey shades. In the P1000 mode this is quite considerably below the target line, resulting in a darker image than intended. It’s still not perfect in the TB400 mode, but it’s much better.
Demonstrating the “problem area” where mid grey input signals between around 45 – 80 lead to poor PQ tracking in the P1000 mode, at higher APL. Here this example is at 50% APL

What does this all mean then?

The end result of all this is that in real HDR content, it is the mid shades that end up looking darker in the P1000 mode than in the TB400 mode in most scenes. That’s because the PQ tracking is much less accurate in P1000 mode for APL above 10%. Apart from in overall very dark scenes with small bright highlights (low APL %) you will probably find that the overall image looks brighter in TB400 mode in many situations.

It’s important to note though that not all parts of the image will look darker, it’s only certain mid shades that are problematic. The darker visible shades should look similar in both modes so you don’t need to worry about dark areas or scenes losing detail or being darker than they should be. The brightest parts of the image, triggered by the light grey > white input signals should also look the same in both modes for most scenes (10% APL and above) as again the PQ tracking is accurate in both modes. So dark and very light parts of the image should look the same, but the mid shade brightness will vary. That is what is causing the overall brightness of the collective image to look darker in P1000 mode.

One other consideration is that for the smallest APL scenes (<10%) the P1000 mode can reach higher brightness for bright input signals (70 > 100). In those situations you can reach the full luminance potential of the panel up to >1000 nits, whereas the TB400 mode caps out around 470 nits.

[Key Update 2] Improved Testing Methodology and Data for our Reviews

We have been working hard over the last few months to extend our HDR testing to provide even more detailed data and analysis. The additional information discussed here will help us more thoroughly consider HDR performance in the future, especially when it comes to the complex area of brightness. We’ve already used this approach in our most recent review of the Gigabyte AORUS FO32U2P in fact.

Luminance Accuracy

For the data in this section we’ve used the MSI MAG 341CQP (34″ ultrawide 2024 line-up) which we recently reviewed, which has the familiar two HDR modes for P1000 and TB400. The trends in this data are are again likely to be very similar across other modern OLED screens covered in this article, including the other MSI models, and those from Dell and Asus. We are using them here more to demonstrate and explain the tables and graphs that we hope to introduce for future reviews.

Peak 1000 mode

As well as providing some EOTF graphs at a few different APL’s beyond just the typical 10% APL measurement in the future, we’ve been working on a useful way to measure and represent what we are going to call the “luminance accuracy” of the HDR modes. The table above is a simple approach which tracks the luminance error. Each grey shade being measured is shown across the top of the table starting from 0 for black, and going through the grey shades until you reach 100 for white. These grey shades are also relevant for mid-tone colours which are basically produced using a greyscale input and a colour filter. So measuring greyscale in this way can provide us a more complete data set, certainly far more than only measuring white luminance as has been the industry norm for a long time. Measurements are taken at a range of different APLs shown down the left hand side, from 1% up to 100% and the measured luminance of each grey shade is compared with the target it should be reaching.

The difference in luminance, whether that’s a positive number where it’s brighter than intended, or a negative number where it’s darker than intended is then captured in the table and colour coordinated. The blue areas are where the luminance is higher, and the pink areas are where it is lower. Ideally for a fully accurate greyscale performance all these squares would be white, which would reflect the ability to achieve the intended luminance for all the different grey shades, and at all the different APL areas. Having said that, as we said earlier it is quite common to have a gentler roll-off for luminance on the higher APL situations, as the absolute peak luminance that can be reached is much lower than at small APL levels, and rolling off a bit earlier helps preserve some light grey details. As a result, some pink-coloured error for larger APL’s in the mid to light grey shades is perfectly acceptable.

Focusing on one section of the same table from before, this time only showing the areas which are darker than intended, you can see the problem here in the peak 1000 mode then which is that for the mid grey shades from about grey 45 up to grey 75, the luminance is lower than it should be, quite significantly in some cases, and this gets progressively worse as the APL increase. This was evident by studying all the different EOTF graphs too, but hopefully this single table is a quicker and easier representation of the “luminance accuracy”.

True Black 400 mode

If we consider the same table for the True Black 400 mode on this screen you can see that although there are still some errors, they are not as drastic and so the achieved luminance is closer to the target luminance for these different grey shades. Remember for now this is just measuring the luminance accuracy, that being how far away it is from the intended luminance. We can also compare the two modes to demonstrate which is brighter in different situations in a moment.

Greyscale luminance

Another potentially good way to represent this data, and also present the measured luminance of the greyscale at the same time, is using this graph above. Here it is calculated for the peak 1000 mode. To do this we have considered an average of the measurements across the mid to light grey shades between 45 and 75 and you can see a visual representation of which shades that covers with the gradient bar under the table on the left. This excludes the much darker shades which should be considered separately as those parts of the image will relate to darker scenes and shadow detail, and are less relevant when considering the overall appearance of brightness in an image. We also exclude those that are near white (from 80 and above), as that’s commonly where clipping occurs on OLED screens since they can’t get anywhere near the 10,000 nits upper limited defined for the PQ EOTF. These grey shades from 45 – 75 are also the interesting area in terms of where problems commonly arise, and which will make up a significant portion of any brighter real-world HDR content areas.

On the graph itself the dotted grey line shows the average target luminance that should be reached for those grey shades, while the pale blue line tracks the average measured luminance for those shades. Ideally the two lines would match if there was no error in the luminance and it was completely accurate. You can see here for Peak 1000 mode that for the smallest APL’s the lines meet closely and the achieved luminance is as intended for the different grey shades. This reaffirms what is shown in the pink/blue table earlier.

However as the APL increases in area, the achieved luminance is quite a lot lower than intended and so is less accurate. It’s saying the same thing as the pink/blue data table shown earlier, but just in a single graphical form for simplicity. We would consider this P1000 mode to have inaccurate HDR luminance tracking, with a tendency for content to be darker than intended. This is especially problematic for large APL scenes (i.e. those which have overall lighter content).

If we look at the same graph for the True Black 400 mode you can see again that the achieved average luminance for these mid to light grey shades is much closer to the target luminance, although there’s still some small error as the APL increases. The luminance accuracy is better here though, only being a little darker than intended.

These tables and graphs not only tell us how accurate each mode is relative to the intended luminance but can also be used to directly compare and consider the achieved luminance of the greyscale. We’ve already shown earlier why taking only white measurements are incomplete and inaccurate, so we can now add in greyscale. It’s a bit like our updates to include colour brightness recently, although we took that a step further as we had to account for not only luminance, but for colour gamut and how bright visually those colours appear.

We think this is a useful approach to identify problem areas, and to measure HDR luminance performance across different monitors. It’s really a much more detailed extension of the single PQ EOTF graph normally provided, which only considers a single APL (10%) and isn’t necessarily as visually simple as these tables and graphs to interpret and compare.

Comparing P1000 and TB400 greyscale luminance

We can also then directly compare the two modes to see how much the actual measured luminance differs by plotting the achieved average greyscale luminance for each mode on the same graph:

You can see a direct comparison then here between a typical ‘Peak 1000’ mode and a ‘True Black 400’ mode. This again explains why in many situations the TB400 mode ends up looking brighter than the P1000 mode in practice.

Conclusion

Hopefully that has been a useful investigation in to these seemingly now common HDR modes on modern OLED monitors. To summarise, a lot of the initial observations seem to stem from users who are viewing SDR content within HDR mode, including the Windows desktop. In those situations the Peak 1000 mode will look darker, and show more obvious shifts in brightness and more common dimming. That applies even to white input signals and tests. Remember though, we would recommend you only enable HDR mode when you are viewing actual HDR content.

Viewing actual HDR content is more complicated, but our continued investigation into the matter and the results from our phase 2 and 3 updates show that in many situations the TB400 mode will provide an overall brighter looking HDR image. That seems to be a result of the better mid-shade PQ tracking in that mode, with the P1000 mode showing poor PQ tracking for many situations. You will have to sacrifice the brightest highlights though for low APL scenes when using TB400.

Ideally the P1000 mode would have corrected PQ tracking for all APL, which should in theory solve this problem and create a scenario where both modes are equally bright in all scenes, except with the P1000 mode being able to push up to the higher peak luminance and reaching 1000 nits in certain scenes (low APL %). That’s logically how these two modes should differ.

We should say that the variation is likely to be different between different manufacturers and screens. It’s not possible for us to take all these measurements on every example. But based on the measurements we have taken, we expect the general pattern of this problem to apply across different models from MSI, Asus and Dell – and maybe others. Based on user reports and feedback, it does seem like it’s a common theme on these new models. In our future reviews we will be able to test this thoroughly. We found the behaviour of the recently launched Gigabyte AORUS FO32U2P (32″ 4K 240Hz) to be very different though, so check out that review for more info and comparisons.

We have fed these findings back to both Asus and MSI for further investigation, and hopefully at some point it might be something they can address through a firmware update. We do not have a direct line of contact to Dell’s product team but have reached out to some contacts we have there. Hopefully they will read this and look in to it as well. We will update this article if we get any further updates and if we carry out any further testing.

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