Ricoh C226 Service Manual page 62

MTF Correction
When the original image is converted to electrical (analog) signals by the
contact image sensor, the contrast is reduced. This is because neighboring
black and white parts of the image influence each other. This symptom is
typical when the width and spacing between black and white areas are
narrow. MTF correction counters this symptom and emphasizes image detail.
The value of a target pixel is modified depending on the value of surrounding
pixels. The modified data are compared with a threshold level. This will
determine if the pixel is to be black or white.
The value [E] of the target pixel [e] is calculated with the following formula:

a+b+c+d+f+g+h+i
E = e +2

e –

After the MTF correction is done, the corrected data are compared with the
black or white threshold level. If a pixel value is above the threshold level, it is
set to black. If the pixel value is equal or below the threshold level, it is set to
white. The threshold level depends on the selected density setting.
Image Density Setting
Lighter
Normal
Darker 1
Darker 2
SM


8

Threshold Level for Line
Mode
28
35
38
42
2-13
OPTICS/IMAGE PROCESSING
Threshold Level for Line
Areas in Line/Photo Mode
35
40
42
44
C226