Unsharp mask

4

Similarly to Photoshop's Unsharp Mask finction, in this step the separated image is made with blurred image (on the separated auxiliary buffer, so it is not visible here). As there is not enough space to do it in the whole frame buffer size, it is performed with (1/5) * (1/5) resolution (every 5th pixel in every 5th row). This unsharp mask will be used for better selecting of "ink" pixels, relative to "paper" pixels, which will be taken not from the main frame buffer, but from the auxilary one.