Gamma (Γ) Correction; Gradation Processing - Gestetner A294 Service Manual

2.3.9 GAMMA (γ γ γ γ ) CORRECTION
Gamma 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 scanner and printer gamma settings can be changed for the 'Service Mode'
original type of text and text/photo modes, using SP4-903-84 and 85.

2.3.10 GRADATION PROCESSING

Various processes are available to try to reproduce various types of original as
faithfully as possible.
The following processes are used in combination depending on the image mode
settings.
1) Three-gradation processing
2) Four-gradation processing
3) Error diffusion
4) Dithering
These three processes are used as follows:
Text Mode:
Text/Photo Mode:
Photo Mode:
Generation Copy Mode: Error diffusion + line width correction, and three-
Pale Mode:
Three-gradation Processing
This mode is used in Photo mode.
The image density data after gamma correction is changed into three-gradation
data (full dot, half dot, or blank) using two thresholds. With this processing, halftone
images are reproduced smoother than with four-gradation processing because of
stable dot image reproduction due to only one intermediate density level.
SM
CÓPIA NÃO CONTROLADA
Error diffusion + line width correction and four-
gradation processing
Error diffusion + line width correction and four-
gradation processing
Error diffusion or dithering, and three-gradation
processing
gradation processing
Error diffusion and four-gradation processing
2-31
CÓPIA NÃO CONTROLADA
IMAGE PROCESSING
A294/A295