HDR Calibration (and KTC M27T20)

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      Hi, you have great reviews, keep up the good work.

      Have a couple of questions for you
      1. What do you think about KTC M27T20 Monitor, do you plan to review it?
      2. Why you dont use Calman software in your reviews, its because of the price?
      3. Is there a way right now to calibrate hdr mode on standart computer monitors?
      Latest version of Windows have – Windows HDR Calibration software, that can make calibration of basic hdr parameters and create icc profile for that mode.
      Can we create similar, but more advanced hdr profiles in other programs to correct colors, pq curve, etc.?

      Thanks in advance


        Hi Dato. I do love a well-structured post so thanks for that:

        1) It’s not a model I’m interested in reviewing, no. It’s an alternative to the Cooler Master Tempest GP27U which is fairly well-reviewed already and you can expect similar performance. For these ‘non-mainstream’ models I personally find the INNOCN 27M2V more intriguing due to it having twice as many dimming zones and it is a model I’ve received some solid feedback for. It performs very nicely based on that feedback and is very good for the price (~$800 USD), though build quality and the funky OSD plus some firmware quirks are the main criticisms. I realise RTINGS has reviewed this one – I requested a sample from INNOCN but they were unable to provide one. It isn’t available locally in the UK and I believe you’re probably not considering it for the same reason, availability where you live.

        2) Whilst cost is a consideration, it’s not a barrier. It simply doesn’t suit our reviewing style which includes extremely detailed subjective analysis that is entirely unique to our reviews. And we’ve already added a lot of additional points of coverage to our reviews and unique things such as the SpyderCHECKR 24 visual analysis, pursuit photography with a broad range of refresh rates and other settings plus subjective HDR analysis using a range of game scenes. I don’t really have the time or inclination to add further analysis from something like Calman. It would likely have to replace rather than reinforce what is already done, which isn’t an acceptable trade-off.

        3) The only way to accurately and appropriately calibrate a monitor under HDR is if it includes hardware HDR calibration. This is very rare unfortunately, with the ASUS PA32DC being the only model we’ve reviewed that includes that capability. Adjusting based on software is pretty futile really, you may subjectively prefer the output but its not really calibration in its truest sense. Mini LED monitors have local dimming algorithms which will affect performance based on content and its brightness levels, whilst OLED monitors have their own inconsistencies due to ABL (Automatic Brightness Limiter) behaviour. If you look at Windows HDR Calibration, it only uses a full screen patch plus single non-full screen patch size and bases certain adjustments on that. This can negatively impact performance for other patch sizes. I’ve also played around with this myself with several monitors and find it’s unable to do much to improve the end result and can never ‘fix’ clear issues with monitor PQ curves or dimming algorithms. It could potentially be useful in some cases, especially for movies and games which don’t include an HDR calibration slider feature. But tweaking with the OSD and calibrating in-game appropriately is really all I’d recommend and for actual calibration it needs to be done on the monitor if that feature is offered (and it rarely is).


          Thanks for your quick and extensive answers.

          Actually few days ago I buy ktc m27t20 monitor, but external power adaptor bundled with it, is not working.
          So cant test it.

          I hope soon there will be a way to calibrate hdr mode on regular computer monitors, like new hdr icc profiles or another system / standard to achieve great color, white balance, etc.


            Hey, quick correction. The M27T20 from KTC is actually a different thing from the GP27U or GP27Q. It’s a 1440p mini-LED backlit monitor like the GP27Q, but unlike that one, the M27T20 actually uses an HVA panel from CSOT. This means it should have some pretty different characteristics, particularly with regards to response times. I’m curious to see a review since I wonder if it will have response times similar to the Samsung Odyssey VA monitors, which also use HVA panels from CSOT, or if these are lower quality panels in some way.


              Ah yes you’re absolutely right, for some reason I thought it used an IPS-type panel rather than VA and didn’t check the specifications recently. Thanks for correcting that, it does indeed make it unique and more interesting. CSOT makes a broad range of VA panels used in a range of monitors, some which are ‘HVA’ specifically, essentially taking over from Samsung Display’s LCD production. Unfortunately the vast majority are significantly slower than the ‘higher end’ Odyssey models, so I wouldn’t expect the M27T20 to necessarily match the likes of the Odyssey G7 or Odyssey Neo G7 and G8 in terms of pixel responsiveness. The Philips 34M2C7600MV and ViewSonic XG341C-2K we’ve reviewed recently for example are Mini LED models with CSOT HVA panels and have relatively weak pixel responsiveness. Hopefully the M27T20 is better than that, but the use of a CSOT HVA panel does not in itself inspire confidence. I’ll check with KTC to see if a sample can be made available, but that wasn’t one of the models they listed in an earlier email so I can’t promise it sadly.


                Have question to PCM2)
                – Do you know program DWM_LUT, with it you can apply 3dlut files to sdr and hdr modes, to correct all inconsistencys!?

                This program from the author of novideo_srgb
                Users discuss it on displaycal forums


                  I’m vaguely familiar with it, something to play around with if you already have a colorimeter or similar device to create useful data for the 3DLUT files, but it’s not the sort of thing that will correct HDR dimming algorithms or tuning.


                    Actually it can calibrate hdr mode pq curve and colors using hdr lut, look at the readme!


                      See my first post in this thread, point 3. Monitors don’t just have a single PQ EOTF curve that can be neatly calibrated under HDR, they behave differently depending on the APL (Average Picture Level) or relative level of dark and bright on the screen. And with Mini LEDs this effect can be extremely localised due to their local dimming algorithms. This tool does not address or change the local dimming algorithm on Mini LED monitors and can’t circumvent the ABL behaviour of OLED screens and the content-dependency of the PQ EOTF curve in different scenarios. So it isn’t able to thoroughly and precisely calibrate the HDR performance, but it could certainly still have a positive effect in some cases by ‘tightening things up’.


                        I agree with you. But still hdr lut can move things in positive ways, correct wb and color more or less


                          Yes, it certainly has its uses on the colour side. 🙂


                            My mini review of KTC 27T20 monitor after some time with it.

                            After I recieve my unit it worked for one day, and then external power supply died, ktc support promise to send me new one from China.
                            While I wait for it, I just buy another power adapter for time being, and monitor is working fine.

                            Some observations using a monitor.
                            – there is slight bending on the left side of the screen, just few pixels, not something major or eye catching, but I dont see this effect ever on other monitors. Many users on reddit and rtings also observe it
                            – algorithm of local dimming prefer to supress blooming, and because of this small highlights are drag dawn a bit, appear not very bright as they should be
                            – compare to my current samsung monitor image on ktc is very sharp, small details stand out more, I try to adjust this using osd of the monitor, but with no luck, dont no what why is that. Maybe it because of the mini led backlight or just monitor tuned this way


                              – a little bit more about sharpness, on my current monitor Samsung C27HG70 image by default look soft, normal, on ktc for example wrinkles on peoples faces look more accentuated
                              – monitor have wide gamut, like ~80% of rec.2020, by default colors look more saturated that they should be, but this is not a problem
                              Main issue is some hues look wrong, in hdr mode more then in sdr, especially affected are red colors
                              Reds shifted towards magenta, oranges towards red, as a result skin tone dont look pleasing, people have red patches on skin, like a sunburn

                              On a plus side mini led backlight is doing its thing, contrast is improved, blacks looks deep, highlights is really bright and punchy

                              Maybe there is firmware update in the works, that can fix some things


                                Thanks for sharing your impressions, Dato. Sounds like you’re enjoying it overall, despite some rough edges. Are you planning to keep the screen?


                                  Dont no yet. I ordered colorimeter, want to calibrate my monitors, compare them.
                                  I will test ktc more, use it a bit and then decide


                                    I test KTC m27t20 monitor more, have a colorimeter right now, some of my findings
                                    – there is slight vignetting towards image borders in SDR mode without local dimming enabled
                                    – after my current curved screen Samsung C27HG70, image on a flat ktc monitor look slighty convex, just need to get accustomed again))
                                    – there is two versions of firmware for US and EU regions. I have EU screen and choose firmware accordingly, but after update there is banding between color transitions in hdr mode and after checking gamut in edid, monitor report primaries close to sRGB space, but this is wcg monitor with QD layer
                                    Then I decide to update my EU screen with US firmware and everything went well, banding in hdr is gone and edid now reporting wide gamut primaries!
                                    Everything else is also working like expected. Dont no why there is two version of firmware exist
                                    – by defaut in SDR mode image is very contrasty, there is sharp transition between highlights and shadows and because of that screen look oversharpend. After calibrating monitor using colorimetr image became normal like on my previous screen!
                                    Out of the box gamma was way off and after profiling it is corrected. Maybe for games and movies its ok, but if you develop raw photos and want right image, one need to calibrate this monitor

                                    So think after all I keep this monitor


                                      Thanks for sharing further thoughts and findings. I’m glad you’ve managed to get around dodgy firmware and poor calibration and are ultimately satisfied enough to keep the monitor. You will get used to the flat screen eventually, when going from reviewing a curved screen to using a flat one of similar size I often get the same sort of ‘convex’ sensation. But it fades over a period of several days for me then isn’t felt at all. It’s odd how the brain tries to compensate in this way. 🙂


                                        For those who like to tweak the HDR representation and/or the SDR representation when using HDR, a utility called ‘ColorControl’ now has added functionality that allows such tweaking. You can edit aspects such as the colour gamut target and gamma (which will affect HDR shade representation). Whilst this won’t give you the precision needed to fine-tune EOTF curves or tweak local dimming algorithms or ABL tuning, if you’re not happy with your monitor’s native HDR performance it is certainly worth exploring and having a play with this. 🙂

                                        This post demonstrates how you can set up a toggle which allows you to easily switch between HDR with adjusted Nvidia Digital Vibrance and SDR with default Nvidia Digital Vibrance. I’ll shortly be publishing a video that gives a quick run-through of this tool. It won’t be a deep-dive but will show off some of its functionality and help raise awareness of the tool, which certainly has the potential to be useful. On the monitor I feature in the video (KOORUI GP01) HDR is very basic and never going to be anything more than that, but it’s also hampered by messed up ‘gamma’ (or EOTF tracking) which can be offset to an extent using the tool. And that’s interesting as it couldn’t be offset using the Windows HDR Calibration App. So depending on the monitor, one method may work better than the other for tweaking. Either way, I definitely see either method as tweaking rather than true calibration of the monitor due to how general and limited the adjustments are. Useful for some screens, nonetheless.


                                          I’ve published a quick video showcasing ‘ColorControl’ and how it can be used for ‘HDR calibration’ (tweaking, really). It isn’t a technical deep dive and doesn’t run through many of the features of the application, but it’s really to raise awareness of the program and encourage people to check it out for themselves.


                                            Now off to HDR considerations… 😉 I have read your article on ICC profiles, did some digging over the internet and there are still questions:
                                            1. Is the SDR ICC profile at all used for HDR content in Windows?
                                            2. Are there any differences in HDR handling between Windows 10 and Windows 11 if one skips the HDR calibration?
                                            3. Does W11 HDR calibration have any impact on gaming on the monitor if most of the games have their own built-in calibration? I assume it’s more useful for TVs?
                                            4. In case of this monitor, in the DisplayHDR mode almost all the control settings are locked – does it mean it’s “calibrated”? Do RGB settings for SDR have impact on HDR colour temperature?

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