Gestetner B147, Service Manual

Page: 486 / 1081

IMAGE PROCESSING
B147/B149/B190 6-28 SM
Picture Element (Dot Position) Correction
Picture element correction does two things.
1. Completion of the scan line correction process.
2. Correction if the CCD is not perpendicular to the light.
•
The green CCD line is taken as a standard.
•
Both ends of the red and blue lines are adjusted to match.
•
Use SP 4-932-1 to 4-932-4 to change the vertical line correction level
(
“3. Replacement and Adjustment – Image Adjustments”).
Scan Line Correction
R, G, and B CCD lines are spaced 4 lines apart (8 lines total) when full size
magnification is used.
• Scan line correction synchronizes these signals by storing each line in memory.
•
The difference between the R, G and B signals depends on the magnification
ratio.
•
If this calculation does not result in an integer, the corrected data is set to the
closest integer, but further correction is needed (
“Picture Element
Correction”).
Image Separation
The machine separates the original image into text and photo (dot screen) areas.
Edge Separation
•
Used to locate text and line diagrams
•
Locates areas of strong contrast.
•
Looks for continuity of black or colored pixels.
• Looks for continuity of white pixels around black or colored pixels.
•
Only uses data from the green CCD.
Dot Screen Separation
•
If white pixels are not detected around non-white pixels, it is a dot screen area.
Colored Text Separation
•
Identifies whether the text area’s pixels are black or color.
•
Based on:
1) Differences among the RGB maximum signal levels.
2) Output levels of the RGB video signals.