When it comes to image resolution, there are several terms that are used.

  • PPI stands for pixels per inch,
  • DPI stands for dots per inch
  • LPI stands for lines per inch.

PPI and DPI are to all intents and purposes synonymous and can be used interchangeably. Each pixel on screen maps to dots (as in dots of ink) when printed. LPI is the number of halftone dots used to reproduce continuous tone in print. Here are some typical halftone screen frequencies. A 600 DPI laser printer uses a line screen of somewhere between 65 to 85 lines per inch. For newsprint, somewhere between 85 and 110. And for coated paper printed on offset press, somewhere between 133 and 200 lines per inch. But don’t just go with these figures. The basic rule of thumb is that for every halftone dot, you need 2 image pixels for best quality. So if you have an LPI or line screen value of 150, your best-quality resolution is 300 pixels per inch.