Ricoh PRIPORT VT 2000 Series Service Manual page 69

28 February '91
2.8 IMAGE SIGNAL PROCESSING : BINARY CIRCUIT
The binary circuit produces 1-bit data (white or black) from the output of the
A/D converter (four-bit data) and sends it to the thermal head board.
2.8.1 Function
1) Line Mode:
MTF (Modulation Transfer Function) Correction Processing
2) Photo Mode:
Dither Processing (Graduation Processing) - 16 graduations
Edge Emphasis Processing (Selection of either MTF or Dither process-
ing)
2.8.2 Outline
1) MTF Correction Processing
This is used to emphasize image signal data compared with surround-
ing pixels. Emphasis data which varies according to the surrounding
pixels is compared to a fixed threshold level to determine if the pixel is
white or black.
Sub Scan
The emphasis data is compared to a threshold level to determine if the
pixel is black or white.
Emphasis Data E
Emphasis Data E
Main Scan
I H G
F E D
C B A
E = 2E -- 1/2(D + F) ------ Main Scan Emphasis Data
2
E = 2E -- 1/2(B + H) ------ Sub Scan Emphasis Data
1
2
2
When the surrounding pixels are
whiter than the pixel being processed
E , the pixel data E is converted to
appear darker than the real pixel data.
This converted data is termed the em-
phasis data.
Conversely, when the surrounding pix-
els are darker than the pixel being
processed E , the pixel data E is con-
verted to appear whiter than the real
pixel data.
≥ 7.5 ----- Black
or E
1
or E < 7.5 ----- White
1
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