In graphic design the abbreviations DPI and LPI are important to images used on the web; and important for halftones and process printing in the print media industry. Below is the information you need to know.
The abbreviation DPI stands for “Dots-Per-In” which is the amount of “dots” per square inch. DPI often affects the size, file size and quality of an image or print. In graphic design, there is standard of DPI that we must adhere to.
The web standard for website images should be 72 DPI. This helps keep the file size of the image to a minimum so pages load faster. The thing with web images is that you should not use them for print media (see below). Typically web images are compressed and the quality is not always the best at 72 dpi. Images are typically in the JPG, GIF and PNG.
The print standard for printed material (magazines, catalogs etc.) is 300 DPI. This allows for photo quality output. When 300 dpi is used on images, it allows an image to be of high quality. The printing industry usually requires all images to be 300 dpi. There are occasions where the print industry will use 150 dpi, but this is typically for low quality printing.
The abbreviation LPI is “Lines-Per-Inch” which is how many lines of dots are in one inch. LPI is used strictly in the print media industry. This setting allows for the adjustment of spacing in between lines of dots. This is often used with angle, screen frequency of the dots, and or to produce halftones.
Screen frequency is the number (1 to 1200 or more) used to adjust the size of dots that is printed on a page. This is used strictly in the silk-screen and printed media industry. Silk-screen printers often use screen frequency (between 30-60) for halftones that is used to produce dots on vellum. The print industry uses screen frequency (300 or more) for controlling quality or graphic effects. The lower the screen frequency, the bigger the dots.