Scanner Gamma - Ricoh Aficio 220 Service Manual

20 September 1999
Scanner Gamma (γ) γ) γ) γ) Correction
The CCD output is not proportional to the quantity of the light received. Scanner
gamma (γ) correction corrects the CCD output so that grayscale data is proportion
to the quantity of the light received.
The machine has four possible scanner gamma curves. The curve used by the
machine depends on the original type selected by the user (at the operation panel
and with 09. Image Mode Adjustment in the user tools). If the user selects one of
the original modes known as 'service mode', the gamma curve can be selected
with SP4-928.
If "0" is selected with SP 4-928, the scanner gamma curve is either AE or NAE,
depending on the selected original mode (text, photo, etc.).
The four gamma (γ) correction curves and their characteristics are as follows:
• Non Auto Exposure ID linear (NAE): Corrects the image data in proportion to the
original density.
• Auto Exposure ID linear (AE): Removes the background from the image data to
some extent and corrects the rest of the image data in proportion to the original
density.
• Reflection Ratio ID Linear (Linear): Uses the image data without correction.
• Removed background (SP): Removes the background area completely and
corrects the rest of the image data in proportion to the original density.
Output
Removed Background
Linear
Original Density
2-19
IMAGE PROCESSING
NAE
AE
SP
A250D550.WMF