YCgCo

The YCgCo color model (or YCoCg) describes the color space formed by luminance Y, chrominance green Cg, and chrominance orange Co. This is supported by video compression codecs such as H.264/MPEG-4 AVC and Dirac[1] since it can losslessly be converted to and from RGB with fewer bits required compared with other color models.

Original image above and representation of the individual components Y, chrominance green Cg and chrominance orange Co.

Comparison with other color models

RGB color model

The three values of the YCgCo color model are calculated as follows from the three color values of the RGB color model:

The values of the luminance Y are in the range from 0 to 1, while chrominance green Cg and chrominance orange Co are in the range of −0.5 to 0.5. For example, pure red is expressed in the RGB system as (1, 0, 0) and in the YCgCo system as (1/4, −1/4, 1/2).[2][3]

The inverse matrix converts from the YCgCo color model back to the RGB color model:

To perform the conversion, only two additions and two subtractions are necessary, and there are no real coefficients. The transformation can be efficiently implemented as integer additions and subtractions: 

tmp := Y   − Cg;
R   := tmp + Co;
G   := Y   + Cg;
B   := tmp − Co;

YCbCr color model

An advantage the YCgCo color model has over the YCbCr color model is simpler and faster computation, and better decorrelation of the color planes to improve compression performance.[2][3]

Literature

Textbook:

Research on YCgCo color model:

References

  1. ↑ "Dirac Specification" (PDF). BBC. p. 136. Archived from the original (pdf) on 2015-05-03. Retrieved 2010-05-04.
  2. 1 2 "YCoCg: A Color Space with RGB Reversibility" (ppt). University of Texas at Arlington. Retrieved 2010-05-02.
  3. 1 2 Yair Moshe. "H.264 Amendment: Fidelity Range Extensions" (pdf). Signal and Image processing Lab (SIPL). p. 15. Retrieved 2010-05-02.
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