Higher ColourSpace licenses (INF/XPT/PRO LMN/LGN & HTX/HTP) have the ability to natively work with larger LUT sizes than the default 33^3 cube, including 256^3 and beyond.
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: that Entering stupidly large values will stop ColourSpace from generating any LUTs - values up to 300^3 have been verified as working 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 33^3 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.
Additionally, the memory required for large LUT generation, such as 256^3 LUTs, means only one LUT at a time can realistically be worked on, and attempting to process more will likely crash ColourSpace. Therefore, make sure to close the LUT Generation window before performing any LUT Upload into systems that can use 256^3 LUT such as madVR.
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 128^3 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 size that is applicable for the desired application, keeping in mind many LUT systems are physically limited to 33^3 or 17^3 sizes. And while initially generating a LUT of a different size to the actual size of the final LUT can be a help, due to Nyquist when down-sampling, or the smoothing effect of the applied filtering when up-sampling, there is really never any real benefit of generating a huge native LUT that is far beyond the final LUT size.
3D LUT Size Issues
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.
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.
1D LUT Size Benifits
An obvious benefits 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 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 + 3D option is 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 user defined Grey Ramp RGB patch set can be used with a large patch count, with a full, but smaller, volumetric patch set used for the 3D LUT.
