Difference between DPI and LPI

Sometimes I'm confused over the difference between DPI(dots per inch) and LPI(lines per inch). What are exactly the differences between the two? Thanks in advance!

IMAGE RESOLUTION
- Image resolution refers to the number of pixels in a linear unit of the image, which is usually in inches.
- Dpi or ppi refers to dots or pixels per linear inch.
- Images are made up of little dots called pixels. Pixel stands for PICture ELment. Put enough of them together and you have a picture.

SCREEN RESOLUTION
- Screen resolution is the number of halftone dots in a linear unit.
- Halftone dots are used in the printing process to simulate tonal values of the image. Larger dots for darker tones and smaller dots for lighter tones.
- Indicated by lpi (lines per inch) or lpm (lines per millimeter)

OUTPUT DEVICE RESOLUTION
- Refers to the number of exposure or printing points per linear unit used by an output device to transfer an image to the output material.
- Indicated by dpi (dot/inch), ppi (points per inch), dpm (dots per millimeter) or ppm (points per millimeter)

The above is basically an outline answer to your question. In my seminar titled "Answers to FAQ’s on Digital Prepress", one of the faq's is "Dpi, megapixels, lpi, ppi – what do these all mean?". It takes about 15 minutes plus Powerpoint to discuss this topic. If you need more explanation, call me at 7190892.

Layman answer:

1) ppi:
Pixels per inch. some are low res at 72 ppi (internet photos); others can be high res at 300 ppi

2) dpi:
Dots per inch. Number of dots per square inch. As the images (ppi) pass the RIP it is now converted into dots.

CtF and CtP dpi would have to be higher at 1200dpi (news); 2400dpi (commercial)

3) lpi:
Lines per inch. Rows of dots in one square inch. Also known as screen frequency. Newsprint can handle between 85lpi to 120lpi. Super calendared or Light Weight Coated will have to be around 133lpi or 150lpi. Depends on screening (AM, FM, XM) and also the capability of the press...commercial offset paper such as Paper Types 1 and 2 can handle 150, 175 and even higher.

Hope this helps.

Thanks for the clear info mga sir!

DPI is for printer resolution. PPI is for image resolution. But for many, it doesn't matter whether it is printer or image.

LPI is used to define the frequency of your halftone dots used in offset/screen printing.

Your DPI defines grey steps in your desired LPI.

Your LPI also dictates the right PPI for your image.

High PPI or pixels per inch doesn't ensure quality printing in digital printing and other electronic print output devices. Printer resolution or DPI also is teken into account.