This step applies only to RGBA component groups,
and is skipped if MAP_COLOR is FALSE.
First, each component is clamped to the range 
.
There is a table associated with each of the R, G, B, and A
component elements:
PIXEL_MAP_R_TO_R for R,
PIXEL_MAP_G_TO_G for G,
PIXEL_MAP_B_TO_B for B,
and PIXEL_MAP_A_TO_A for A.
Each element is multiplied by an integer one less than
the size of the corresponding table,
and,
for each element,
an address is found by rounding this value to the nearest integer.
For each element,
the addressed value in the corresponding table replaces the element.