Ricoh C226 Service Manual page 64

OPTICS/IMAGE PROCESSING
Binary Processing in Letter/Photo Mode
In the Letter/Photo mode, the machine checks each pixel of the original to
see if the pixel is in a line area or in a photo area. To recognize a line area in
a photo original, the CPU does the following calculation on the 6-bit pixel data.
x = | (c + f + i) - (a + d + g) |
y = | (g + h + i) - (a + b + c) |
If x or y is greater than 10, the machine will recognize that pixel e is in a letter
area of the image and uses the MTF process to convert the 6-bit value to
1-bit.
If the calculated number is 10 or less, the pixel is converted to 1-bit using
Error Diffusion.
To emphasize characters in a photo original when using Letter/Photo mode,
a data compensation curve (γ curve) is used to make a darker image.
SM 2-15 C226