- This topic has 1 reply, 2 voices, and was last updated 7 years, 8 months ago by
.
-
Posts
-
Hi Florian
Please may I ask for your help on some questions regarding DisplayCAL creating 3D LUTs which also contain the calibration data:
– How does DisplayCAL’s 3D LUT contain the calibration data for the user’s monitor as well as a transform between colour spaces?
– If you are creating a 3D LUT only (no ICC) to colour correct a monitor (viewing REC709 media on a REC709 monitor) where the grading software can load a display 3D LUT, how does the calibration data from the instrument/Argyll get integrated into the 3D LUT?
– Is it technically better to load the calibration for the monitor from a 3D LUT, rather than a 1D XYZ LUT in the ICC for Windows?
– In “3D LUT” tab, if “apply calibration (VCGT)” is set, where does the VCGT data come from? Is the VCGT calculated during the calibration process, then integrated into the 3D LUT? If the “Calibration” tab’s “Tone Curve” is set to “as measured”, then surely the calibration contains no gamma calibration for the user’s monitor, so where does the 1D XYZ LUT/VCGT get calculated to be integrated into the 3D LUT?
– I created 2 3D LUTs in DisplayCAL from an sRGB profile, one file exported with “apply calibration (VCGT)” applied, and the other file without “apply calibration (VCGT)” applied, but both 3D LUT files appear the same in a text editor. Should they not be different if one contains the VCGT data?
– Also, if the source media is REC709 and the monitor is REC709, is the 3D LUT not required, as there’s no transformation between colour spaces? Or is the 3D LUT still handling monitor calibration too? Is it just the 1D LUT that is used for the monitor calibration?
– What is the relationship between the “tone curve” on the “Calibration” tab and the “3D LUT” tab? Do they do different things when the ICC/3D LUT are loaded by the OS/application?
– Don’t 3D LUTs get loaded into the Nvidia graphic card, not just 1D LUTs? Nvidia cards ignore the loaded ICC profile when in full screen mode?
– Does the 3D LUT tab create a device linked ICC profile and put a 3D LUT inside the ICC file? What happens to the XYZ LUT? Is that also inside the ICC file along with the 3D LUT?
– Does Windows 7 use the device linked ICC file and the embedded 3D LUT, or does Windows 7 just use the 1D LUT?
Many thanks for any kind assistance!
Warm regards,
JohnHi,
– How does DisplayCAL’s 3D LUT contain the calibration data for the user’s monitor as well as a transform between colour spaces?
– If you are creating a 3D LUT only (no ICC) to colour correct a monitor (viewing REC709 media on a REC709 monitor) where the grading software can load a display 3D LUT, how does the calibration data from the instrument/Argyll get integrated into the 3D LUT?
You can’t create a 3D LUT without first creating a profile. The profile characterizes the monitor, the 3D LUT then transform from a fixed input colorspace (e.g. Rec 709 Bt 1886) into the monitor colorspace.
The 1D calibration data is simply incorporated into the overall transform.
– Is it technically better to load the calibration for the monitor from a 3D LUT, rather than a 1D XYZ LUT in the ICC for Windows?
It is less flexible, but has the benefit that you are not reliant on possibly flaky ICC profile support in applications (and most applications in the video world don’t support ICC color management anyway, so a 3D LUT is often the only way to get color correct output to a very high degree of accuracy).
– In “3D LUT” tab, if “apply calibration (VCGT)” is set, where does the VCGT data come from?
From the display profile.
Is the VCGT calculated during the calibration process, then integrated into the 3D LUT?
Yes.
If the “Calibration” tab’s “Tone Curve” is set to “as measured”, then surely the calibration contains no gamma calibration for the user’s monitor
It’s simply linear in that case (same effect as no 1D calibration).
– Also, if the source media is REC709 and the monitor is REC709, is the 3D LUT not required, as there’s no transformation between colour spaces?
If the monitor really adheres to the target with a high level of accuracy, then yes, the 3D LUT won’t (need to) change the signal much.
– What is the relationship between the “tone curve” on the “Calibration” tab and the “3D LUT” tab?
For a 3D LUT, it doesn’t matter what the 1D calibration tone curve is set to – the 3D LUT tone curve overrides it. That’s why for all the 3D LUT presets, 1D calibration is basically disabled (“As measured”).
– Don’t 3D LUTs get loaded into the Nvidia graphic card, not just 1D LUTs?
There are no graphics cards with 3D LUT capability that I know of, the video card gamma tables (videoLUT) can only contain 1D curves.
Nvidia cards ignore the loaded ICC profile when in full screen mode?
Graphics cards generally have no notion of ICC profiles or 3D LUTs. Applying color management is application-level functionality (i.e. support needs to be specifically built into each application), or in the case of 3D LUTs, may be done using external hardware (e.g. external 3D LUT box). An exception to this is Mac OS X where the OS itself has a fully color managed desktop, but some 3rd party applications may still be limited in their support for color management.
– Does the 3D LUT tab create a device linked ICC profile and put a 3D LUT inside the ICC file?
A device link is basically just a standardized 3D LUT file format, just like ICC profiles. The difference is the colorspaces they map to and from: ICC profiles map from device space (=RGB for display devices) to device independent space (CIE L*a*b* or XYZ) and vice versa, and can be linked on the fly, providing a high level of flexibility. 3D LUTs are baked transforms created from linking such colorspaces.
– Does Windows 7 use the device linked ICC file and the embedded 3D LUT, or does Windows 7 just use the 1D LUT?
Windows 7 has only very limited (and buggy) support for ICC profiles itself, and no support for 3D LUTs at all. The only thing that affects the display globally is the 1D videoLUT, because it is loaded into the graphics card.
