Ricoh SP 200 Specifications download pdf (Page 33)

1. Grayscale Processing

As stated on the previous page, this process generates up to 64 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), and will be explained in the Laser Exposure section.

Briefly, the width of the laser pulse for a pixel depends on the output level

(from 0 to 63) required for the pixel.

For each pixel, the location of the active (laser on) part of the pixel can be either

at the left side of the pixel, at the center, or at the right side (see fig 2). The

machine determines which method to use depending on the settings of SP

2-903. There are different settings for pixels at the left edge, at the right edge,

and in the middle of a series of black/grey pixels across the main scan, and for

single black pixels with white pixels at the left and right. The edges of characters

and lines become clearer with this processing.

2. 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 4-418.

The printout density of the black pixel depends on the pixel type (left, center,

or right of a series, or isolated, in the same way as for grayscale processing).

These values can be adjusted with SP2-904.

Fig. 2

A193D507.wmf

Fig. 1

A193D518.wmf

IMAGE PROCESSING 1 August 1996

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Ricoh SP 200 Specifications Page 33