Ricoh LDD250, Руководство по обслуживанию

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IMAGE PROCESSING
C262/C265 6-18 SM
6.3.2 AUTO SHADING
There are two auto shading methods: black level and white level correction. Auto
shading corrects errors in the signal level for each pixel.
- Black Level Correction -
The CPU reads the black dummy data from one end of the CCD signal (64 pixels
are blackened at the end) and takes an average of the black dummy data. Then,
the CPU deletes the black level value of each image pixel.
- White Level Correction -
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 ECU board.
The video signal information for each pixel obtained during image scanning is
corrected by the ECU board.
Auto shading for the first original is done before the scanning.
After scanning every page, auto shading is done to prepare for the next page.
If the copy image density or the original mode is changed during the copy run, the
auto shading for the next scan is done before the scanning to respond to the mode
change.
C262D008.WMF