A Tour up the Gray Scale Vector of the RGB Color Cube: How Computer Graphics Color Spaces Relate to Digital Video Color Difference Space

In the RGB color space, where color is defined by relative intensities of red (R), green (G), and blue (B), the gray vector is defined by the RGB color cube diagonal where R, G, and B are all equal. This paper takes the reader on a tour up the gray vector within the RGB color cube, starting from black (R=G=B=0) and moving to white (R=G=B=1). Along the way, we stop and examine special color planes perpendicular to the gray vector. At a point one-third of the way up the gray vector, the plane has vertices defined by the pure red, green and blue primary colors of the RGB color space. Continuing to halfway up the gray vector, each edge of the color plane intersects one of six sides of the RGB cube, each intersection at a midpoint. This “halfway” plane forms an equilateral hexagon and is used to describe how RGB space and HSV (or HLS) space are related. At two-thirds the way up the vector the plane has vertices defined by the complementary colors to the pure red, green and blue; these are the pure magenta, yellow and cyan points in the RGB color cube. — Then, using the definition of Rec. 601 for standard color difference space Y, B-Y, R- Y (or YCBCR) within a digital video signal, we show geometrically how this relates to both the standard RGB cube and the HSV color space in 3- D and in various 2- D color plates. These relationships lead to insights and knowledge of YCBCR color space and how computer graphics color space differs from digital video color space. — The formulations and color plates generated in this paper will provide the reader with a more intuitive and analytical understanding of how computer graphics color spaces and video color difference space relate. This should prove useful in the development of computer- generated color graphics for video production and helpful to individuals developing color-processing algorithms such as color correction, color enhancement and color for streaming video content.

Published

2001-11

Content type

Original Research

DOI

10.5594/M00976

ISBN

978-1-61482-935-5