RICOH AFICIO 450
Instrukcja Serwisowa

IMAGE PROCESSING

26 March 1998

Grayscale processing
As stated on the previous page, this process generates up to 256 image density levels for each pixel. To realize this, this machine uses a form of pulse width modulation. In this machine, pulse width modulation consists of the following processes: � Laser diode pulse positioning � Laser diode power/pulse width modulation Laser diode power and pulse width modulation is done 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.

Binary picture processing
Each video signal level is converted from 8-bit to 1-bit (black and white image data) in accordance with a threshold value. The threshold value can be adjusted with SP 4-904-12.

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).

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