Ricoh Gestetner 5450, Service Manual, Page: 38 / 315

IMAGE-PROCESSING 1 July, 1998
2-10
2.2.5 BINARY PROCESSING
In the IPU chip, the 8-bit data is converted into 1-bit data for black or white pixels.
The binary processing for the letter mode is different from that for the photo mode
and the letter/photo mode as follows:
1) Letter mode: Binary processing
2) Letter/Photo mode: Binary processing
3) Photo mode: Binary proc error dif dithering
These processes are used as follows.
- Binary Processing with Gamma Curve Compensation -
This process converts each video signal level from 8-bit to 1-bit (black and white
image data) in accordance with a threshold value.
The threshold value changes based on a compensation curve (Gamma curve)
which corresponds to selected image settings. For example, if a darker image is
selected, a compensation curve, which converts each pixel value to a higher
number, is selected. This ensures accurate generation of the gray scale from black
to white.
- Error Diffusion - (Photo mode only)
The error diffusion process reduces the difference in contrast between light and
dark areas of a halftone image. This process corrects each pixel using the
difference between it and surrounding pixels. It then compares the corrected pixels
with the error diffusion matrix.
- Dithering - (Photo mode only)
Dithering compares each pixel with a pixel in the dither matrix. Several matrixes
are available, to increase or decrease the detail on the copy.