Gestetner B147, Service Manual

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IMAGE PROCESSING
B147/B149/B190 6-36 SM
Auto Color Calibration Test Pattern
The test pattern has eight 17-step
gradation scales for each color (CMYK),
including background white, for Text
and Photo modes.
ACC automatically calibrates the printer
gamma curve. The user starts the ACC
process.
1. The user prints an ACC Test
Pattern.
2. The user places the test pattern on
the exposure glass.
3. The copier makes 8 scans to read
each color scale.
4. The copier corrects the printer
gamma by comparing the ideal
settings with the current image
density.
5. The copier combines the corrected
gamma curve with the Shadow,
Middle, and Highlight values
currently in memory.
6. The copier then calculates the ID
max (amplitude of the gamma curve) based on data from the ACC scan.
7. The corrected printer gamma curves can be adjusted further using SP modes
(SP4-909 to SP4-918).
Error Diffusion
Error diffusion reduces the difference in contrast between light and dark areas of a
halftone image. Each pixel is corrected using the difference between it and the
surrounding pixels. The corrected pixels are then compared with an error diffusion
matrix.
IPU Board Test
You can check the IPU board with the SP mode menu, SP4-904-1 or 2.
(
“4. Troubleshooting” for details)
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Dark Light
B146D520.WMF