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10 February 2005
Scanner Gamma Correction (RGB Gamma Correction)
The RGB video signals from the CCD are sent
to the ASIC1 chip on the BICU board. This
signal is proportional to the intensity of light
reflected from the original image (Fig. 1).
Scanner gamma correction inverts the video
signals. The shading circuit converts the signal
from 10-bit to 8-bit.
• The ASIC1 chip converts the signal levels as
shown in Fig. 2.
• This improves the accuracy of RGB to CMY
color conversion (conversion is done later in
the image process).
• The same table is used for R, G, and B
signals.
Filtering
Appropriate software filters are applied to the
RGB video signals.
• Varies depending on the results of auto
text/photo separation (or on the selected
original mode).
• RGB smoothing is applied to photo areas
• Edge emphasis applied to text areas.
Background Density Control
• Removes low ID image signals (background) that are less than a certain
threshold.
• The threshold depends on the color mode (single color or full color).
Users can select a different threshold for each mode.
ADS (Auto Image Density Selection)
• Full color mode
1) Refers to the RGB data taken from the entire original.
2) Calculates a threshold for removing the background based on this data.
• Black and white mode
1) Determines the peak white level.
2) Peak level data is taken for each scan line.
3) Removes the peak white level from the image. This produces a white
background.
4) Also uses the peak white level to determine the white reference value for
A/D conversion.
5) Background density is adjusted before data is input to the A/D converter.
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Fig. 1
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Fig. 2
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IMAGE PROCESSING
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