The number of pixels generated by the gbr2greyscale RIP can be hundreds of millions. Often the system that uses the bitmap does not need the entire data set in one very large file. Therefore the program enables the output bitmap to be broken into a number of bands or tiles.
Often when a bitmap is divided, it is also necessary to include some extra data surrounding each tile so that there are no discontinuities where the tiles butt up against each other.
Consider that we start with a working image area of 530 mm by 630 mm and divide it horizontally into 9 equal stripes as shown below:
Now take the first stripe and define an expansion region of 200 pixels all the way around it as shown below:
Normally a bitmap is output with the reference location at upper left and by row from left to right as shown below:
Depending on the application the end user may need that the upper right be the reference point and that the pixels be ordered by column starting from the left most column and working in the right direction.
We are packing 4 pixels into a byte; this is how they are placed into the byte stream.