Ricoh A250 Service Manual page 75

ID Gamma (γ γ ) Correction
ID Gamma ( γ γ ) ) Correction
Image adjustment (08) in the user tools
Mode
Text Toner Saving
Text/Photo
Photo
The machine automatically selects the most appropriate ID gamma correction
based on the selected original type (and the user tool Image Adjustment setting)
and ID setting made at the operation panel.
When the user selects "Service Mode" for any original type (User Tools - General
Features - 08. Image Adjustment), you can use SP4-940 to change ID correction in
service mode. The types that can be selected with SP4-940 are different for each
original mode (Text, Text/Photo, or Photo).
Gradation Processing
Image adjustment (08) in the user tools
Mode
Text Toner Saving
Text/Photo
Photo
Overview
The 8-bit image data is converted into 1-bit data (there is no 8-bit greyscale
processing, only the 1-bit process known as binary picture processing).
However, different techniques are used, depending on the selected original type
(text, text/photo, photo) and user tool Image Adjustment setting.
These techniques are simple binary picture processing, error diffusion, and
dithering. To see which process is used, see the flow charts in the Image
Processing Summary section.
• Simple binary picture processing: Each video signal pixel is converted from 8-bit
to 1-bit (black and white image data) in accordance with a threshold value.
• Error diffusion: Error diffusion is a more complex process using a threshold value
and the values of nearby pixels in an 8 x 8 matrix. In text/photo mode, e rror
diffusion reduces the difference in contrast between light and dark areas of a
halftone image. In text mode, it prevents parts of low contrast text from
disappearing from the copy.
• Dithering: Each pixel is compared with a pixel in a dither matrix.
SM
Default
Normal
— Photo Priority
Coarse Press Print
Default
Normal
— Photo Priority
Coarse Press Print
2-17
IMAGE PROCESSING
Sharp (Service Mode)
Text Priority (Service Mode)
Glossy Print (Service Mode)
Sharp (Service Mode)
Text Priority (Service Mode)
Glossy Print (Service Mode)
A250