22 October 1999IMAGE PROCESSING
2.3.9 GAMMA g() 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,
Detailed
laser diode, and lenses).Descriptions
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-graduation processing
2) Four-graduation processing
3) Error diffusion
4) Dithering
These three processes are used as follows:
Text Mode:Error diffusion + line width correction and four-
graduation processing
Text/Photo Mode:Error diffusion + line width correction and four-
graduation processing
Photo Mode:Error diffusion or dithering, and three-graduation
processing
Generation Copy Mode: Error diffusion + line width correction, and three-
graduation processing
Pale Mode:Error diffusion and four-graduation processing
Three-graduation Processing
This mode is used in Photo mode.
The image density data after gamma correction is changed into three-graduation
data (full dot, half dot, or blank) using two thresholds. With this processing, halftone
images are reproduced smoother than with four-graduation processing because of
stable dot image reproduction due to only one intermediate density level.
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ACEC
