M66335FP Datasheet, PDF (14/59 Pages) Mitsubishi Electric Semiconductor – FACSIMILE IMAGE DATA PROCESSOR

M66335FP
(3) Image Processing Function
The M66335 converts image signals input from the image sensor into binary data. This includes the simple conversion
of characters and the change of images with various densities into pseudo-half-tone.
Before the conversion, distortions and characteristic degradations which signals from the image sensor almost always
have must be corrected or compensated.
Image zone separation must also be performed to realize optimal conversion-to-binary of the image for the possible
shortest transmission time.
Functions required for image processing are as follows.
• Peak value detection
• Uniformity correction
• Resolution change (enlargement, reduction and averaging)
• MTF compensation
• γ correction
• Background/character level detection (simple conversion to binary)
• Change to pseudo-halftone
Organized dither
Error diffusion
• Image zone separation
• Designation of regions
Peak Value Detection
Because the A/D converter of the M66335 uses the input dynamic range at 2 Vp-p, the reference voltages (V_WL, V_BL)
corresponding to the peak value are fixed. The peak value of analog signals output from the analog processing circuit
must be detected before those signals are input to the A/D converter in order to adjust the analog signal peak value to
the full-scale value of the converter.
The peak value detection is performed by reading white data from the sensor in the AGC mode selected from its three
modes (AGC, UNIF and SCAN) of the M66335.
As shown in figure 4, preprocessing of peak value detection to increase the gain at the gain control is performed for a 8
line cycle and gain control processing to decrease the gain when the A/D converter over-flows is performed for another
8 line cycle after the start command (register 00: AGC) in the AGC mode.
As a result, the gain changes as shown in figure 5.
Peak value detection
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Line cycle
Preprocessing of peak
value detection
(increasing the gain)
Gain control on the
peak value
(decreasing the gain)
Figure 4 Peak Value Detection
REJ03F0276-0200 Rev.2.00 Jun 16, 2008
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