After a recent conversation with a user, it has become apparent that not all users/calibrators understand the importance of the order of LUTs in a signal path, or what impact making alterations to a display's calibration - either changing individual LUTs, or making manual adjustments - has on the underlying display calibration.
We have added to the section on Manual adjustments within the
Calibration Issues page of the website, as well as on the specific User Guides pages for displays and LUT boxes with multiple LUT capability.
In simple terms, making any adjustments to a display after LUT based calibration will break the calibration.
However, the order of the LUTs and/or manual adjustments within the signal path has a real impact on the level of issues that will be caused if changes are made.
If there are multiple LUTs in use within a signal path, after any individual LUT is uploaded into a display any additional LUTs must only be added, or adjusted, in front of the first LUT - never after.
So, any display or LUT box that has a back-end 1D LUT with a 3D LUT in front should have the back 1D LUT calibrated first, and with that LUT active, the display re-profiled and a 3D LUT generated an uploaded.
Never in the reverse order.
For optimal calibration, the better LUT order is 1D followed by 3D, with both LUTs being treated as a single entity, with an optional back-end 1D LUT.
ColourSpace always provides the best possible options for any LUT based calibration, regardless of the signal path in use.
For
3D -> 1D LUT signal paths, the first, and the usual default, is to null both LUTs in the display, and perform a large volumetric profile with ColourSpace – potentially with the addition of Augment, a Focused Patch Set, etc.
Then generate the normal 3D LUT within ColourSpace.
As ColourSpace works to a much higher resolution than the LUTs used with displays/LUT boxes, and in full float, the LUT is very accurate.
The LUT can then Upload using the 3D + 1D option.
This means ColourSpace will separate the 1D LUT from its internally generated large 3D LUT, and upload that to the 1D slot, with the remaining 3D LUT component uploaded into the 3D slot.
So, from the single profile and large ColourSpace LUT generation, the display will have the best possible 1D LUT, and the best possible 3D LUT.
Together, they provide a level of granularity that very closely matches the inherent calibration LUT generated within ColourSpace.
If the display is particularly unstable there may be benefit gained with doing the ,1D LUT first, potentially using a large Grey Only profile, uploading it, and then re-profiling with a 3D volumetric profile for the 3D LUT upload.
With a
1D -> 3D LUT signal path, The same workflow can be used, nulling both LUTs in the display, and perform a large volumetric profile – potentially with Augment, etc., generating the normal 3D LUT within ColourSpace, and Uploaded using the 1D + 3D option to again separate the ColourSpace internal 3D LUT into individual 1D & 3D LUTs for upload.
However, is is again possible to first perform a volumetric profile, and generate and upload a 3D LUT, and then perform a Grey Only profile with the 3D LUT uploaded, and generate a 1D LUT for separate upload.
For
1D -> 3D -> 1D signal paths, the back 1D LUT must be performed first, if used, and then the 1D + 3D LUTs uploaded, either simultaneously, or separately.
Steve
Steve Shaw
Mob Boss at Light Illusion