Ricoh LDD250, Service Manual

Page: 342 / 459

IMAGE PROCESSING
C262/C265 6-20 SM
6.3.5 CENTERING
The timing for uploading data from the SBU is delayed, and the writing start
position is changed to the center. (The standard writing position is in the corner.)
6.3.6 BINARY PROCESSING
In the ECU board, 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.
6.3.7 ERASE SHADOW
The shadow at the centre of a book, borders of originals and so on are erased
automatically. This mode is activated when master making is started while the
platen cover or ADF is open.