2.3.3 Color Space

RawGfx Mode distinguishes between 3 types of color spaces: palette indexed, RGB, and YUV. Any of those spaces may be combined with an Alpha channel, which defines blending transparency.

Eventually all color formats are rendered to the monitor in RGB space. Palette indexed formats use a colour palette, which is an RGBA lookup table with 2^bpp entries. YUV formats use a YUV-to-RGB conversion matrix. RGB formats obviously can be output directly.

For palette indexed formats, pixels are stored as indices into the palette lookup table of 32-bit AABBGGRR values:

                    [R]
Palette[ index ] => [G]
                    [B]
                    [A]

For YUV formats, a 3x3 conversion matrix with a pre-conversion offset vector is applied to convert YUV to RGB pixels, the Alpha channel is used directly:

  [Y]   [Y_offset]     [ a  b  c ]    [R]
( [U] + [U_offset] ) x [ d  e  f ] => [G]
  [V]   [V_offset]     [ g  h  i ]    [B]

  [A]                              => [A]

• JFIF - as used in Jpeg images
• YCbCr SDTV (ITU-R BT.601)
• YCbCr HDTV
• YIQ NTSC
• Kodak PhotoYCC