Ricoh K-C3 Service Manual page 221

B245/B276/B277/B268/B269 Service Manual
Auto Shading
Overview
There are two auto shading methods: black level correction and white level correction. Auto
shading corrects errors in the signal level for each pixel.
Black and white level correction is always done.
Black Level Correction
The IPU detects the black dummy data from one end of the CCD signal (32 pixels at the end
are blacked off) and takes the average of the black dummy data. Then, the black level value
from each image pixel is detected.
White Level Correction
Previous machines used 8-bit data (256 gradations), but this machine uses 6-bit data (64
gradations). When white level correction is applied to 8-bit data, white lines are more easily
generated. This is because the normal variations in CCD pixel response (which are very
slight), when rounded off by white level correction, will show up much easier on the copy
when the data is divided into 256 gradations.
Before scanning the original, the machine reads a reference waveform from the white plate.
The average of the white video level for each pixel is stored as the white shading data in the
FIFO memory in the IPU (SCRATCH) chip.
The video signal information for each pixel obtained during image scanning is corrected by
the IPU (SCRATCH) chip. If the maximum value of the video level is 64 or less, SC101
(exposure lamp error) is generated.
Auto shading is done before scanning for the first original as well as after scanning each page
to prepare for the next page.
If the image density or the original mode is changed during a copy run, auto shading is done
before scanning the next original.
White Line Erase
The white line erase feature is validated (default) when you specify a value other than "0" in
SP 4941 1. This feature works as follows:
1. The copier scans the original.
2. The density level of each pixel is compared with its adjacent pixels.
3. If the density level of a pixel is extremely lower then adjacent pixels, the
level is corrected. The density levels of the adjacent pixels are considered.
When you validate the white line erase feature, the feature works for all originals. This feature
erases the white lines of 1- through 6-pixel width (approximately, up to 0.25 mm). The white
lines that exceed this width are not erased.
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