Gestetner B147, Service Manual

Page: 488 / 1081

IMAGE PROCESSING
B147/B149/B190 6-30 SM
Scanner Gamma Correction (RGB Gamma Correction)
The RGB video signals from the CCD are sent to the IPU section. This signal is
proportional to the intensity of light reflected from the original image (Fig. 1).
Scanner gamma correction inverts the video signals. The shading circuit converts
the signal from 10-bit to 8-bit.
•
The IPU section converts the signal levels as shown in Fig. 2.
•
This improves the accuracy of RGB to CMY color conversion (conversion is done
later in the image process).
•
The same table is used for R, G, and B signals.
255
0
255
Light Dark
B146D512.WMF
255
Dark Light
0
1023
B146D513.WMF
Fig. 2
Fig. 1