Mtf Correction; Binary Processing In Letter/Photo Mode - Ricoh C231 Service Manual

IMAGE-PROCESSING

MTF Correction

When the original image is converted to electrical 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 is compared with
a threshold level. This determines if the pixel is to be black or white.
After the MTF correction is done, the corrected data is 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

Binary Processing in Letter/Photo Mode

In the Letter/Photo mode, the machine checks each pixel of the original to see if
the pixel is in a letter area or in a photo area. To distinguish letter and photo areas,
the CPU does the calculation on the 6-bit pixel data.
If the CPU recognizes that the pixel is in a letter area of the image, it uses the MTF
process to convert the 6-bit value to 1-bit.
If the CPU recognizes that the pixel is in a photo area of the image, the pixel is
converted to 1-bit using error diffusion.
To emphasize characters in a photo original when using Letter/Photo mode, a data
compensation curve ( curve) is used to make a darker image.
C231/C237/C238
Threshold Level for Line
Mode
28
35
38
42
2-14
Threshold Level for Line
Areas in Line/Photo Mode
35
40
42
44
SM