Ricoh Aficio Color 4006, Service Manual

Page: 89 / 487

IMAGE PROCESSING 24 February, 1999
2-40
(2) Scanner Gamma Correction (RGB Gamma)
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:
Dark (Black) Light (White)
Scanner Input (RBG) 0 1023
After
γ
Correction (RGB)
↓
255 0
Color Conversion
↓
Printer Output (CMYK) 255 0
1023
Dark Light
0
A259X008.WMF
2 5 5
0
1 0 2 3
Light D a r k
A259X009.WMF
Image Data
RGB Signal After
Scanner
γ
Correction
Image
Data
Scanner
Input
Fig. 1
Fig. 2