Lines per inch ( LPI ) is a measure of print resolution . A line consists of halftones, which are physical dots of ink made by the printing device to create different tones.
Specifically, LPI is a measure of how close the lines in the halftone grid are to each other. The quality of the printer device or display determines how high the LPI will be. High LPI shows more detail and sharpness.
Printed magazines and newspapers often use a halftone system. Typical newsprint is not very dense and has relatively high dot gain or color bleed, so newsprint is usually around 85 LPI.
Higher quality papers such as those used in trade magazines have less dot gain and can go up to 300 LPI with quality glossy (coated) paper. To effectively use the full range of LPI available in a halftone system, an image selected for printing generally needs to have 1.5 to 2 times more samples per inch (SPI).
For example, if the target output device can print at 100 LPI, the optimal range for the source image would be 150 to 200 SPI. Using SPI less than this will not make full use of the printer's available LPI; using SPI more than this will exceed the printer's capability and quality will effectively be lost. Another device that uses the LPI specification is a graphics tablet.
Converting between lines per inch and lines per cm
Countries that use the metric system tend to use lines per centimeter (L/cm).
The following formulas can be used to convert between L/in and L/cm:
Lines per inch - Lines per cm: L/cm = 0.394 x L/in ie 254 L/in = 100 L/cm Lines per cm -
Lines per inch number: L/in = 2.54 x L/cm
so 100 L/cm = 254 L/cm