HP 4550 Service Manual - Page 246

Understanding color variations The printed output might not match the computer screen, and the colors printed on successive pages might not match. While color variations are inherent in this printing method, they can indicate changes in the printing environment, print media, or printer components. Common causes of color variation The following list outlines the major causes of color variations between computers, applications, and output devices.
Halftone patterns produced on monitors and the types of patterns used in the print jobs are different and might cause variations in the printed output.
The printed output differs from the image on the monitor because the monitor and the print media have different reference values of black and white. The monitor screen has charcoal gray for the black level, and the white on the monitor screen is actually blue. Black on the print media is limited only by the fill capability of the printer, and most good quality paper has a very high white level. In addition, phosphor (used in color monitors) and toner have entirely different spectra characteristics and different color-rendering capabilities. Differences between output are common. Blues generally match better than reds.
The color of the ambient light changes the perception of color. Fluorescent light lacks many colors present in incandescent light, and the color range of natural light is broader than any artificial light. When comparing color, choose a standard light source for reference and understand that the perceived color will change as the light changes.
Long-term color variations occur as paper ages. Use high-quality paper and protect the paper from sunlight to help minimize discoloration.
Environmental changes can cause color variation. The development process places a high potential across an air gap to attract toner to the imaging drum. Changes in relative humidity vary the point at which the toner travels to the imaging drum.
All consumable components have a finite life span. As these components reach the end of their useful life, their ability to produce consistent print quality diminishes.
Paper roughness can cause colors to look different. Use standard paper. Color selection process The user selects the color in the application, but the operating system might convert or modify some characteristics of the color before sending the information to the printer driver. The printer driver might also modify color characteristics depending upon the selected output mode. Any color characteristics not addressed by the printer driver or applications are set to the printer default. The default color might not match the color the user selected. Customizing color output through printer drivers The printer driver, which is installed with your printer software, enables your software applications to use the features of the printer. It also gives you customized control of color text, graphics, and photos. The method of using your printer driver depends on your computer's operating system. For specific instructions about using printer drivers, see the printer driver's Readme file, which is included on the printing system CD-ROM. The following color control features are available only through your HP printer driver. See the printer driver's online Help for details about color settings and their effect on printed output. 244 Troubleshooting C7085-90921