2. These density patterns are transferred to the ETB, and the color registration detection
unit measures the image density of these patterns. Image data is returned to the
formatter.
3. The formatter uses the image data to perform a halftone calibration in order to obtain an
ideal halftone image.
Image density detection
Each of the image stabilization controls described above uses the color registration unit at
the top of the ETB unit to measure image density. To measure image density, the DC
controller emits a light from sensors located above the density detection patterns on the
ETB. The light reflected off the patterns is returned to the sensor, and the data is returned to
the DC controller.
Figure 5-31. Image density detection illustrates this process.
When the values detected by the density sensor are outside the specified range, the DC
controller resets the image density and issues an "image density sensor out of guaranteed
range" warning to the formatter.
If the sensor receives no reflected light, the DC controller stops the printer and issues a
"density sensor abnormality" warning to the formatter.
Figure 5-31.
Image density detection
168 Chapter 5 Theory of operation ENWW
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