Ricoh A250 Service Manual page 69

Scanner Gamma (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 08. Image 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
SM
Reflection Ratio ID Linear
2-11
IMAGE PROCESSING
NAE
AE
SP
Original Density
A250D550.WMF
A250