Comparative Study on Required Bit Depth of Gamma Quantization for Digital Cinema Using Contrast and Color Difference Sensitivities

Abstract

A specification for digital cinema systems which deal with movies digitally from production to deliv- ery and projection on the screens is recommended by DCI (Digital Cinema Initiative), and systems based on this specification have been developed and installed in theaters. The parameters of the sys- tems that play an important role in determining image quality include image resolution, quantization bit depth, color space, gamma characteristics, and data compression methods. This paper compara- tively discusses a relation between required bit depth and gamma quantization using both of a human visual system for grayscale images and a color difference model for color images. The required bit depth obtained from a contrast sensitivity function against grayscale images monotonically decreases as the gamma value increases, while it has a minimum value when the gamma is 2.9 to 3.0 from CIE 1976 L*a*b* color difference model. It is also shown that the bit depth derived from the contrast sen- sitivity function is one bit greater than that derived from the L*a*b* color difference model at the gamma value of 2.9.