In association with the Entertainment Technology Center
In digital movie-making, craftspeople with many specialties are involved with color image data representing elements of the movie. Model makers, materials specialists, animators, rotoscope artists, lighters, shaders, and compositors all have a hand in manipulating the color values that ultimately produce the colors in the movie. However, several different color systems are used to represent image data at various points in the pipeline. HSL and HSI are typically used for color selection; RGB is used for image generation; nonlinear R'G'B' is often used for storage, and SDTV Y'CBCR is used for preview. Different color spaces are used for measurement and calibration - CIE XYZ, xyY, and LAB. Finally, Cineon/DPX or HDTV Y'CBCR coding systems are likely to be used for mastering and film recording.
In this seminar, we help the film craftsperson understand the perceptual and technical reasons why all of these representations are necessary, and how they relate to each other. We introduce the critical importance of perceptual coding, and explain why mid gray - 50% of the way up Photoshop's RGB scale - is only 18% intensity. We explain the fundamentals of the transforms between various color representations. We outline color management systems, and the associated ICC profiles, that have been deployed in film production to maintain accurate color through the pipeline.
Colors are altered depending upon their context in the image; we describe aspects of visual perception that are important in the selection of colors. For example, yellow and brown have identical CIE XYZ values - the difference is whether the surrounding area is dark or light. Reproduction of accurate color depends upon technical parameters of display equipment. We introduce display primaries, white point, and contrast ratio; we examine the effect of these parameters upon reproduced color, and describe methods of compensating the differences. Color appearance depends upon the ambient environment at the display; we explain why colors look different at different displayed intensities.
Finally, although color science provides an essential technical foundation for creating and maintaining accurate color, we discuss some weaknesses of color science, and identify the areas where craft and art will always rule.
Charles Poynton -