HP PCL/PJL reference (PCL 5 Color) - Technical Reference Manual

5-14 The PCL Print Model EN
For example, the logic equation for ROP 252 in the RGB color space
is T OR S, which is shown as TSo in Table 5-4. The truth table for the
ROP is shown above, and can be seen to correspond to the logic
equation TSo, that is, D gets the value of T OR S without regard to the
current value of D. Furthermore, the binary value of 252 is 11111100
and corresponds with the value of the D for all the combinations of T
and S, when the truth table starts with (1, 1, 1) and ends with (0, 0, 0).
It’s possible to derive the logical operation for a truth table and to
create a truth table for a logical operation. However, the most
important point is that the binary value of the ROPs number gives the
Destination for all possible combinations of Texture, Source, and
Destination.
The way the bits of the ROPs number map to the combinations of
Texture, Source, and Destination depends on whether the color space
is RGB or CMY. The least significant bit of the RGB ROP value maps
to (0, 0, 0), the color black in RGB, and the most significant bit to
(1, 1, 1), white in RGB. On the other hand, the CMY ROP reverses
the mapping. This reversal hinges on the fact that RGB and CMY are
the inverse of each other, i.e., RGB Black is (0, 0, 0) and CMY Black
is (1, 1, 1), white. All other colors show the same relationship.
ROPs in the RGB Color Space
The RGB ROP truth tables shown in Table 5-1 illustrate how ROP 252
and ROP 90 work, and most importantly how the bits in the ROP map
show destination values for each combination of Texture, Source and
Destination. A “1” in the RGB color space represents white and a “0”
black, which makes determining what shows on paper cumbersome
for users since the paper is marked when the Destination has a “0”
value.