Canon 1000 Service Manual page 94

3. OPERATION AND TIMING
i. Removing the Background (adjusting the background level)
When the CCD reads the light reflected by an original, it also reads the color data of the surface of the
paper (background). In this block, the surface of paper (background) is identified for correction of image
signals, thereby preventing fogging of white backgrounds and improving reproduction quality.
Pixels are identified as representing the background of an original if they tend to appear most frequently
in the sample image data collected during pre-scanning and, in addition, if the level of the R, G, and B signals
is 200 or more (Figure 3-324).
255
200
B
"Background level adjustment" in user mode has two sub modes: mode A and mode B, each using a
different method of correction.
In mode A, only background pixels are processed; the color of the background is removed by correcting
the level of the RGB signal of the pixels to 255.
In mode B, the RGB signals of the background pixels are removed from the image data for the entire
image area. This way, the image on the back of the copy is removed if the copy is transparent enough to let
the back image show through.
3-50
COPYRIGHT © 2001 CANON INC.
G
R
Background pixel
Figure 3-324
CANON CLC1000/1000S/3100 REV.2 MAY 2001 PRINTED IN JAPAN (IMPRIME AU JAPON)
255
200
B
G
R