A Review of 3D-LUT Performance in 10-bit and 12-bit HDR BT.2100 PQ

Abstract

The use of the 3-D-LookUp-Tables (3D-LUTs), during cinematic production and post-production, has proven to be both flexible and faster when performing color transformations or when seeking to give a particular look to a captured scene. Unfortunately, the dimension of the 3D-LUT is limited by the available space in the processing hardware, so there must be a tradeoff between the precision of the transformation (to avoid visual artifacts such as banding) and the space required to store it. Nowadays, not only professional equipment but also commercial televisions are able to display gamut wider than DCI-P3 with a higher dynamic range. The new standard for a High Dynamic Range (HDR) television is now International Telecommunication Union-Radiocommunication (ITU-R) Recommendation BT.2100, which has a color gamut that is almost double the size of ITU-R Recommendation BT.709. Our aim was to determine the required minimum size of a 3D-LUT in the BT.2100 color conversion that avoids unnecessary visual artifacts. We found that tetrahedral interpolation outperformed all others for both Standard Dynamic Range (SDR) and HDR applications. It can achieve the same quality of trilinear interpolation using a 3D-LUT 20%–25% smaller on average. In 10-bit SDR, a 3D-LUT larger than 41 × 41 × 41, if using the trilinear interpolation, and larger than 31 × 31 × 31, if using the tetrahedral interpolation, should result in unnoticeable interpolation errors. In 12-bit HDR, a 3D-LUT larger than 72 × 72 × 72, if using the trilinear interpolation, and larger than 55 × 55 × 55, if using the tetrahedral interpolation, should result in unnoticeable interpolation errors. The saturated and dark images resulted in a much larger minimum size 3D-LUT to achieve a just noticeable difference < 1, thereby confirming the findings by Pieri and Pytlarz that IC T C P might not be suited for those types of images. Finally, reducing the bitdepth from 12 to 10 bits requires considerably larger 3D-LUTs to obtain the same image quality.