Printer Color Correction - Tektronix Phaser 550 Service Manual

5
Theory of Operation

Printer color correction

5-16 Phaser 550 Color Printer
Manual . The color density of each primary color can be selectively altered by
the user. Color adjustments can be made manually using front panel Calibrate
Colors menu. This involves printing a reference page, comparing the reference
page to sample colors on the printer's Quick Reference Card and entering value
changes through the front panels. This process is described in the Phaser 550
Color Printer User Manua l and well as in the Chapter 9 topic, "Manually setting
color corrections" on page 9-32. The changes are sent to the image processor
board, which makes calculations and then downloads a color correction table to
the print engine control board. The color correction table indicates the exact
laser beam pulse duty cycle to the desired colors.
Semi-automatic . You start this self-calibration process using a front panel key
sequence described in the Chapter 9 topic, "Starting printer semi-automatic
color correction" on page 9-32.
The printer features a unique ability to measure how much toner it is depositing
on the accumulator belt for a specific density of color. During this
self-calibration sequence, the printer exposes a portion of the photoconductive
belt with predetermined, stepped values of energy to produce a saturation
dither pattern for each color. In each case, a certain, expected amount of toner
should be transferred to the accumulator belt for each step. Reflective sensors,
located adjacent the accumulator belt, optically sense how much toner was
actually transferred to the accumulator belt; this is called the printer's
densimetric response. This response data is transmitted to the image processor
board, which makes calculations and then downloads a color correction table to
the print engine control board. The color correction table indicates the exact
laser beam pulse duty cycle to produce properly saturated colors.