blue_mask
blue_div = 256 / (cm.blue_mask + 1);
blue_mul = 256 / (cm.blue_mask + 1);
cm->blue_mask = 0x0F;
cm->blue_mask = 0x0FF;
cm->blue_mask != vcm->blue_mask) {
cm->blue_mask = vcm->blue_mask;
cm->red_mask = cm->green_mask = cm->blue_mask = 0x3f;
cm->red_mask = cm->green_mask = cm->blue_mask = 0xf;
cm->red_mask + 1, cm->green_mask + 1, cm->blue_mask + 1);