Higher ColourSpace licenses (INF/XPT/PRO LMN/LGN & HTX/HTP) have the ability to natively work with larger LUT sizes than the default 333 cube, including 2563 and far beyond.
With the x64 version of ColourSpace 3D LUT sizes of 10243 are possible!
Using large LUT sizes has a number of potential benefits for both 3D LUTs and 1D LUTs.
LUT Generation Size
With higher ColourSpace license levels, the native LUT size used is defined from the Main Menu, from the Preferences option. Select LUT Generation Size, and enter the required cube size.
Note: The x64 version of ColourSpace is now the standard version, and LUT sizes of 10243 and beyond have proven to work. The Win32 version is retained only as a temporary fallback for anyone encountering issues following the major x64 changes, and is being phased out - with the Win32 version, large values can potentially cause LUT generation to fail, with values over 2563 verified only on PCs with decent resource availability.
3D LUT Size
The defined native LUT Size is a global setting, meaning that any LUT imported into ColourSpace will be converted into the defined size, so for a LUT to remain at its original size means the native LUT size defined within ColourSpace has to match the imported LUT.
For the generation of large native LUT sizes beyond the initial default 333 size the greater the CPU power and number of threads, the faster the LUT processing. Low power PCs may take an impossibly long time to process very large size LUTs, particularly when using the temporary Win32 fallback version.
Additionally, the memory required for large LUT generation, such as 2563 LUTs that can be used with madVR, means the x64 version of ColourSpace should be used, so we assume that is the case within this info page.
Also, due to the processing involved, Gamut Mapping is a single core process, and will therefore slow down LUT generation considerably when enabled on profiles that target a colour space that is larger than the display's native gamut.
With Gamut Mapping disabled, as should be used for any grading display, processing will use all CPU threads enabled, making the process considerably faster.
Even on less powerful PC systems, native LUT generation up to 2563 should work with no issues, and has been tested on an old i3 CPU, 4 GB RAM laptop.
It is always best to select a native LUT Generation Size that is greater than the desired final application size. Generating a LUT of greater size than the actual size of the final LUT can be a significant benefit, due to the likes of Nyquist when down-sampling.
There really is major benefit in generating a native LUT that is far beyond the final LUT size!
3D LUT Size Variations
The LUT size (LUT Granularity) of any applied LUT also has a direct impact on calibration accuracy, depending on the underlying display issues. Therefore displays or LUT boxes with small internal 3D LUT capability can potentially show different calibration accuracy when the ColourSpace LUT is uploaded, if the uploaded LUT is smaller than the LUT generated within ColourSpace.
For displays that have poor underlying volumetric colour variation, including grey scale, the difference will be less colour accuracy throughout, as above.
Note: The above Verification profile resolution for both is identical, to better show the LUT Size variation.
If the display has a stable, linear native response, the main variation will be the level of backlight contamination/colour error within the near black shadow range, due to the lower granularity of the 3D LUT.
Large 3D LUT Generation Size Benefits
When the final uploaded 3D LUT size is small there is still major benefit in using a far larger LUT Generation size within ColourSpace, due to a combination of standard Nyquist over sampling, as well as a more accurate extraction of the final smaller 3D LUT from the larger generated LUT.
This is easier to visualise looking at the 1D LUT graph, but the benefits are volumetric, and so extend throughout the whole 3D LUT volume.
The above 2 LUTs have been generated from the exact same profile, which was a reasonable BCC 213 profile. As can be seen, the smaller 333 LUT generated from the profile has inaccuracies that the 2563 LUT corrects.
When extracting the final smaller LUT for Upload from either of the 2 above results it is entirely possible that the points in the Uploaded LUT will not align with any of the LUT Generation points, meaning that the final Upload small LUT would definitely benefit from being extracted from the larger initial 2563 LUT.
Note: While ColourSpace graphs plot simple linear interpolation between points, the final LUT Extraction uses Tetrahedral interpolation, but the issue of the relative inaccuracy of generating an initial smaller LUT stands.
Using larger LUT Generation Sizes really will improve final calibration accuracy, regardless of the final LUT Upload size.
This is also where the difference between calibration systems becomes concrete. The smaller, less accurate result above is comparable to a system limited to a 333 internal generation size - which is the case with Calman, whose engine is internally capped at 333 regardless of the final uploaded LUT size. ColourSpace can generate natively to 10243 and beyond, and extract the final upload LUT from that far more accurate volume. For the full comparison, see ColourSpace vs Calman.
1D LUT Size Benefits
Following on from the larger 3D LUT Size benefits, an additional obvious benefit of setting a larger native 3D LUT size within ColourSpace is the resulting increased resolution of any 1D LUT extracted from the 3D LUT, for LUT applications where 1D LUTs can be uploaded independently from the volumetric 3D LUT.
For example, with hardware that correctly has the 1D LUT before the 3D LUT, with the 1D LUT being a larger step count than the size of the 3D LUT, setting the native ColourSpace LUT Size to a value greater than the hardware's 3D LUT size will have a direct potential improvement in the accuracy of the 1D grey scale calibration when the 1D Only, or 1D + 3D options are used to Upload the LUTs.
For hardware with the 1D after the 3D the normal two stage workflow will need to be used, with the 1D LUT being generated and uploaded first, with the display re-profiled with the 1D LUT active, and a 3D LUT generated and uploaded.
As the 1D LUT has already been uploaded, the LUT Tools can be used with the 3D LUT to Null the 1D component of the 3D LUT before uploading, ensuring the 3D LUT doesn't impact the previously uploaded 1D LUT.
For independent 1D LUT generation a large Grey Ramp RGB, or preferably a large Primary & Secondary Ramp patch set can be used with a large patch count, with a full, but smaller, volumetric patch set used for the 3D LUT.
(A smaller 3D LUT, but still larger than the final Upload LUT Size as defined above.)
