Image Data; Creating Colors - Tektronix Phaser 440 Service Manual

5
Theory of Operation

Image data

Creating colors

5-4 Phaser 440 Color Printer
A Phaser 440 print engine must receive data in a specific format to correctly
print the image that the data represents. The printer's image processor board
must convert the data into the correct format. The following topics describe
some of the data formatting that the host or the interface module must perform.
The print engine prints an image in a raster format, line by horizontal line, dot
by dot. The image to be printed is "described" with the colors yellow, magenta,
cyan and black. First the yellow raster making up the image is printed, then the
magenta raster is printed, and finally, the cyan raster. It is the responsibility of
the image processor board to communicate the image data, serially, to the print
engine, in this order.
As mentioned earlier, a Phaser 440 print engine prints only the colors cyan,
magenta, yellow and black. However, these colors, called primary colors, can be
mixed together to simulate other colors, called secondary colors. When tiny
dots of two primary colors are intermixed, your eye perceives a third color. That
is how the print engine can use just three basic colors to create multi-colored
images. For example:
Cyan and yellow intermixed produce green.
Cyan and magenta intermixed produce blue.
Yellow and magenta intermixed produce red.
Mixing yellow, magenta and cyan produces the color black.
It is the responsibility of the image processor board to output, to the print
engine, the CMY-encoded data in the proper sequence to produce the desired
shade.