Canon LBP7660Cdn Manual page 608

[Grayscale Conversion]
RGB]
[Graphics]: [sRGB],
[NTSC], [Uniform
RGB]
[Image]: [sRGB],
[NTSC], [Uniform
RGB]
When it is set to [NTSC], it calculates the grayscale value
using the NTSC standard color conversion method.
When it is set to [Uniform RGB], it takes the average value
of the Red, Green and Blue color values as the grayscale
value.
If [Color Mode] is set as [Auto (Color/Black)] and [Color],
the setting for this item becomes invalid.