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Hello
I am curious to know whether Profile Loader is compatible with HDR display modes. Or should I say: are Microsoft and GPU vendors still implementing the vcgt when in HDR display modes? If so, are there any side effects like banding or interpolation artefacts given the vcgt is only 256 rows.
Thanks!
Hi,
when Windows switches to HDR mode, the whole desktop will be processed, leading to a very harsh contrasty look. I would expect the video card gamma tables are still applied in HDR mode.
If so, are there any side effects like banding or interpolation artefacts given the vcgt is only 256 rows.
The number of entries is not an issue, only the effective bitdepth of the output buffer and whether or not the video card drivers make use of it (with an 8 bit output buffer, the graphics card should apply dithering to prevent banding).
Thanks Florian.
I was looking into it some more and apparently Windows uses the HDR10 standard which uses the BT.2100 PQ curve. It seems in theory it should be possible to use the vcgt to target the PQ curve? Does that sound right to you, or will things still look wrong?
It seems in theory it should be possible to use the vcgt to target the PQ curve?
For desktop calibration, that seems less useful. You only want the display in HDR mode in specific situation (watching HDR movies, maybe HDR compatible games if such exist on Windows)
Oh I see. Yeah I guess that makes more sense to just run the desktop in regular SDR mode. From what I’ve been reading, Windows doesn’t actually render the desktop in HDR but just tonemaps SDR into the HDR space so it basically looks identical to SDR anyway, albeit at some brightness level hard-coded by Windows which would seem to suck. Maybe in the future MS will remaster all the GUI elements for HDR, or maybe web content starts using HDR and then HDR at the desktop might become a thing.
If I calibrate the desktop with HDR off, 8-bit RGB, and Gamma 2.2, will the calibration and colour profile still be accurate for HDR on, 10-bit YCbCr420? Doesn’t the PQ curve also affect this? How will colour aware software work with the SDR profile while HDR is switched on? And what about different luminance levels? Most people calibrate SDR to 100+ nits while HDR with the PQ curve absolutely must be calibrated to 100 nits.
Do I have to manually switch profiles in Windows? I assume 3D LUT is not affected by this since I just need to create one per mode and choose the correct one before playback.
If I calibrate the desktop with HDR off, 8-bit RGB, and Gamma 2.2, will the calibration and colour profile still be accurate for HDR on
No.
Most people calibrate SDR to 100+ nits while HDR with the PQ curve absolutely must be calibrated to 100 nits.
True HDR usually has around 1000 Nits (for HDR10).
True HDR usually has around 1000 Nits (for HDR10).
I believe with all processing switched off the display is expected to follow the PQ curve strictly at least up to 100 nits (diffuse white). Above that is up to the display. I don’t think any decent HDR display should even require gamma calibration. And I guess colour correction can be performed up to luminance values of 100 nits. Or if you measure the display’s curve with fixed settings, can you colour correct accordingly up to its peak luminance?
I believe with all processing switched off the display is expected to follow the PQ curve strictly at least up to 100 nits (diffuse white). Above that is up to the display.
No. The display should follow the PQ curve as closely as possible, rolling off any values that would otherwise be clipped (e.g. using BT.2390, the knee start for the roll-off on a 1000 cd/m2 peak HDR display would be 317 cd/m2).
I don’t think any decent HDR display should even require gamma calibration.
You can calibrate however you see fit. In HDR mode, you’d calibrate to PQ (or use a 3D LUT, which is the better approach because calibrating via 1D curves will not maintain the correct hues and saturations).
And I guess colour correction can be performed up to luminance values of 100 nits.
There’s no upper limit.
What about colour aware desktop applications that use ICC profiles and don’t support 3D LUT? Should these be calibrated as usual in 10-bit RGB (1080p) or 10-bit YCbCr420 (4K) mode but to PQ curve while HDR is on? Do you know if Windows remembers the profiles independently for HDR on and off? I read that it does remember the colour format settings separately.
Can an RGB profile be used with YCbBr or are they incompatible?
For normal desktop operation, it makes no sense to put the display into HDR mode.
Ok, but what happens when I switch it to HDR mode? Won’t DisplayCal Profile Loader load the incorrect calibration from the HDR off ICC profile?
