Halftone and LPI (Lines Per Inch) are two terms that can be used interchangeably to signify how large or small the dot clusters created by the halftoning process will be.

Four-color printing

In four-color printing there are four halftone screens that are used, one screen for each of the four toner-colors. The HP Color LaserJet 1500, 2500, 4500, 4550, 4600, and 5500 series printers only uses three screens. The black and yellow toner colors share the same halftone screen. These halftone screens have to be specifically arranged in order to eliminate or minimize moire patterns, banding and other Print Quality defects, flaws or artifacts. If custom halftones were sent to the printer, there would be a significant increase in all of these print quality defects. This feature, of allowing and recognizing custom LPI/halftones, is available in monochrome printer firmware because there is only one halftone screen, for black toner, being used. The chance of seeing increase moire patterns by adjusting this single screen is unlikely.

Custom LPI settings

The HP Color LaserJet 1500, 2500, 4500, 4550, 4600, and 5500 series printers will not recognize or accept custom LPI settings. The firmware does not allow for custom LPI/halftone commands. This constraint allows customers to get the best possible print quality in as many different printing scenarios as possible.

If LPI settings are needed, that are very different from the predefined ColorSmart II settings, then place the desired image into a program that will allow the user to manipulate it. Once the image is in this type of an application, the user can manipulate the LPI/halftone of the image itself. The image, although printed with the default LPI, will appear to have the LPI value that was specified in the application.

Default LPI settings

The default settings for LPI (also known as halftone screen frequencies) within the HP Color LaserJet 1500, 2500, 4500, 4550, 4600, and 5500 series printers are as follows:

Text Detail:	Detail	212 LPI
Photo and Graphic:	Smooth	155 LPI

Users can also select from two other predefined values should they want a different LPI setting. Text can be changed to Smooth (155 lpi) and Photo and Graphic can be changed to Detail (200 lpi). These selections are available under the ColorSmart II settings within the drivers.

Using ColorSmart II settings