Gestetner B003 Service Manual page 316

IMAGE PROCESSING
Main scan magnification and reduction
Reduction and enlargement in the sub scan direction is achieved by changing the
scanner speed. However, reduction and enlargement in the main scan direction
are handled by the IPU chip.
To reduce or enlarge an image, imaginary points are calculated that would
correspond to a physical enlargement or reduction of the image. The image density
is then calculated for each of the imaginary points based on the image data of the
nearest four true points. The calculated image data then becomes the new
(reduced or enlarged) image data.
γ γ γ γ correction
Gamma (γ) correction ensures accurate generation of the various shades in the
gray scale from black to white, accounting for the characteristics of the scanner
and printer.
Scanner gamma correction corrects the data output to the IPU to account for the
characteristics of the scanner (e.g., CCD response, scanner optics).
Printer gamma correction corrects the data output from the IPU to the laser diode
to account for the characteristics of the printer (e.g., the characteristics of the drum,
laser diode, and lenses).
The data for the scanner and printer gamma correction are fixed and stored in the
memory. There are no SP adjustments in this machine.
Gradation processing
These are three types of gradation processing:
1. Grayscale processing: This has 256 output levels for each pixel.
2. Error diffusion: In text/photo mode, this is used with grayscale processing.
3. Dithering: In photo mode, this is used with grayscale processing.
These three processes are used as follows.
Text mode
Text/photo mode:
Photo mode:
Generation mode:
Pale mode
Type 1: Grayscale processing. As stated above, this process generates up to
256 image density levels for each pixel. To realize this, this machine uses a form of
pulse width modulation. In this machine, pulse width modulation consists of the
following processes:
B003/B004/B06/B007
Grayscale processing
Error diffusion (256 levels)
Dithering (256 levels)
Grayscale processing + line width correction
Grayscale processing
6-34 SM