Minolta Di450 Service Manual page 40

Given below is the control flow when the Auto Exposure mode is selected.
Scanning original fed through EDH
<Realtime scanning>
The Scanner starts reading the
original.
(The copy cycle is started.)
The image data read by the CCD sensor is transmitted (in parallel) from the
Shading Correction block to the Histogram block, where the data values are
sampled, and the samples are counted in order to generated the reflectivity his-
togram.
The CPU determines the type of the original based on the histogram, and sets
the removal threshold accordingly.
The CPU transmits the threshold value to the IR Density Correction block. This
block then corrects the image density of incoming data in accordance with the
relation shown below.
Output
X
0
-b
The gradation curve of the density-corrected data is adjusted in accordance with
the Image Quality mode so as to enhance the reproduction of the high-density
areas.
The above processing helps retain density detail within characters and other high-
density areas, while removing the fogging component from the low-density areas.
Start Key ON
X=aχ-b
X: Image density value after density correction
a: 1
χ: Image density value before density correction
-b: Threshold (intercept)
Input
x
4002M517AA
M-20
Scanning original placed on glass
Document
<Scanning during prescan motion>
The Scanner starts reading the origi-
nal as it starts moving to the original
scanning position.
(Prescan motion is started.)