24 February, 1999LASER EXPOSURE
Gradation Control (Laser Pulse Width and Laser Power Modulation)
PM (32 levels)
Data: 0 Data: 16 Data: 32Data: 48 Data: 64Data: 136 Data: 255
32
24
16
8
PWMDetailed18 112258
(8 levels1 dot)Descriptions
A259D505.WMF
Black
White
Data255A259D506.WMF0
To make the latent image, the laser beam illuminates the image area on the drum
surface. The longer the laser is on and the more intense it is, the darker the
developed pixel becomes. Modulating (changing) the width of the pulse makes the
length of time that the laser is on longer or shorter. There are eight possible pulse
width levels in this model.
While the laser is on to make one dot, the intensity of the laser is controlled by
power modulation (PM). The laser?s intensity is controlled by the amount of current
sent to the laser diode. Modulating the power makes the laser brighter or dimmer.
There are 32 possible power levels, or laser intensity levels.
The laser engine can use the 8 pulse width levels and 32 power levels to create
the 256 possible grayscale values for each pixel for each color.
The power is modulated ONLY at the end of the active part of the on/off cycle of
the laser pulse. For example (see the diagram above), to make a pixel with a
grayscale value of 48, the laser pulse width level for that pixel will be 2. The first
period of the pulse will be at the full power (32), and the second period will be at
power 16 to make up the remainder of the 48 (32 + 16 = 48).
The LD power for each grade is defined by process control.
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ACEC
