Image Processor; Image Rendering Technology - Tektronix Phaser 550 Service Manual

5
Theory of Operation

Image processor

Image rendering technology

5-18 Phaser 550 Color Printer
The image processor board handles PostScript data sent from a host computer
and transforms it into a format suitable for the print engine. The
hardware/software structure that performs this function is called a graphics
pipeline. The graphics pipeline is composed of five basic parts.
The I/O serializer handles the communication and protocol with the
parallel and SCSI port as well as communication with the installed
network card. The particular installed network card handles Ethernet,
LocalTalk or serial communication protocols.
The PostScript data received through the I/O serializer is routed to the
PostScript interpreter. The PostScript interpreter generates display lists
which describe objects and text fonts as they are to appear on the
printed page. As needed, the PostScript interpreter reads font data
stored in ROMs on the image processor board. The PostScript
interpreter also handles errors it encounters in the PostScript data.
The PostScript interpreter's display list is, in turn, routed to the
rasterizer. The rasterizer converts the objects and fonts into a
bitmapped image composed of color planes. Color planes are bitmaps
of the primary colors cyan, magenta and yellow that make up the
image.
The engine driver outputs the color bitmaps to the print engine. It
handles the data transfer buffering and basic input/output functions.
The control loop, which oversees the operation of the graphics pipeline,
routes the color planes to the engine driver that transmits the color
plane data to the print engine. The control loop also monitors the
control and error signals fed back from the print engine.