Gestetner B003 Service Manual page 317

• Laser diode pulse positioning
• Laser diode power/pulse width modulation
Laser diode power and pulse width modulation is performed by the laser diode
drive board (LDDR). Briefly, the width of the laser pulse for a pixel depends on the
output level (from 0 to 255) required for the pixel.
This machine can also change the laser pulse position (at the left side of the pixel,
at the center, or at the right side) automatically, depending on the location of the
image pixel so that the edges of characters and lines become clearer. There is no
SP mode adjustment for this, unlike in some earlier models.
Note that binary picture processing (one bit per pixel) is not used for copy mode.
However, it is used for printer and fax mode. In binary picture processing, each
pixel is converted from 8-bit to 1-bit in accordance with a threshold value. The
threshold value can be adjusted with SP 4-904-12.
Type 2: Error diffusion. This is used only in text/photo mode. The error diffusion
process reduces the difference in contrast between light and dark areas of a
halftone image. Each pixel is corrected using the difference between it and the
surrounding pixels. The corrected pixels are then compared with an error diffusion
matrix. Separate error diffusion matrixes are used for copy mode and fax mode.
1. Grayscale processing mode
The output image signal level has 9 levels (from white to black). There is only
one matrix available.
2. Binary picture processing mode
The output image signal level has just 2 levels (white and black).
Type 3: Dithering. This is only used in photo mode. Each pixel is compared with a
pixel in a dither matrix. Several matrixes are available, to increase or decrease the
detail on the copy.
1. Grayscale processing mode
The matrix type can be selected with SP4-904-2.
2. Binary picture processing
The matrix type can be selected with SP4-904-18.
Line width correction
This function is effective only in Generation Copy mode.
Usually, lines will bulge in the main scan direction as a result of the
negative/positive development system that is used in this model. So, pixels on
edges between black and white areas are compared with adjacent pixels, and if the
pixel is on a line, the line thickness will be reduced.
The line width correction type can be selected with SP4-903-75~77.
SM 6-35
IMAGE PROCESSING
B003/B004/B006/B007