Ricoh Aficio Color 3006 Service Manual page 89

IMAGE PROCESSING
(2) Scanner Gamma Correction (RGB Gamma)
Image Data
1023
0
Dark
Fig. 1
The RGB video signals from the CCD are converted to 10-bit digital signals in the
scanner section and sent to the IPU section. These signals are proportional to the
intensity of light reflected from the original image (Fig. 1). However, the IPU section
converts the signal levels as shown in figure 2 by using a gamma (γ) correction
table in order to improve the accuracy of RGB to CMY color conversion, which is
done later in the image process. The same table is used for R, G, and B signals.
The scanner gamma (γ) correction inverts the video signals and converts the signal
from 10-bit to 8-bit as outlined in the following table:
Scanner Input (RBG)
After γ Correction (RGB)
↓
Color Conversion
↓
Printer Output (CMYK)
Scanner
Input
Light
A259X008.WMF
Dark (Black)
0
255
255
RGB Signal After
Scanner γ Correction
2 5 5
0
Dark
Light (White)
2-40
24 February, 1999
Image
Data
1 0 2 3
Light
Fig. 2
A259X009.WMF
1023
0
0