HP PCL/PJL reference (PCL 5 Color) - Technical Reference Manual

1-2 Color Printing Overview EN
Working with color documents
A document can be thought of as a series of text characters, vector
graphics objects and images. The parts of a document either have
color specifications in them, as do color images, or have color
specifications applied to them, as do color vectors or text. For color
images, the PCL 5 command set provides a way to specify the color
format so that the image data can be interpreted correctly. For vector
graphics and text, the PCL 5 color commands support the application
of a color from a palette of colors.
Each color printed is synthesized from a combination of three colors:
Cyan, Magenta, and Yellow. The way the three colors are combined to
produce the desired color is called a half-tone, and the PCL 5 color
command, Render Algorithm, specifies which half-tone to use for a
color. Advances in Hewlett-Packard printers have allowed HP to
reduce the number of render algorithms to Best, High, and Low. While
the actual implementation of each of these algorithms may vary from
printer to printer, HP has determined that the three algorithms are
sufficient to produce high quality color documents containing text and
graphics.
The colors that appear on a page also have one of two color
treatments applied to them:
1 Screen Match (sRGB), which provides the best WYSIWYG color.
This is the default color treatment.
2 The Vivid color treatment, which provides access to the entire
device gamut (range of colors the printer can produce). However,
these colors are less correlated to those shown on a monitor than
colors that have had the Screen Match treatment applied.
The following factors form the heart of the PCL color graphics state:
• The palette of colors to be used in a document
• The render algorithm to print the colors
• The color treatment to be applied to each color
Palettes of colors can be referenced by an ID, and so can PCL color
graphic states. At any given time there is an active palette to apply
colors from, along with a render algorithm and color treatment to be
applied to the colors. Palettes and their associated render algorithm
and color treatment can be stored and retrieved using a palette ID.
When a palette is retrieved and made the active palette, the render
algorithm and color treatment stored with the palette are set as the
current render algorithm and color treatment.