Information Processing > Resolution

What is resolution on your computer screen?

Digital images are made up of very small spots, called pixels or "picture elements". Every pixel on a computer screen (or television set) has a single color, made of a mixture of red, green and blue light (RGB standard). Computer screens typically can display 1,280 pixels horizontally and 1024 pixels vertically (a total of 1.3 megapixels), but they range from 800 x 600 pixels to 1,800 x 1,440 pixels and better. This is called screen resolution.

If you display at 100% a picture file with more pixels than the screen can show, you see only part of the picture, and must scroll around to see the whole picture.

The resolution of a picture on the screen can also be given as the number of pixels per inch ppi (1 inch = 25.4 mm) measured on the screen. The more pixels per inch, the better the quality of the image. Computer screens typically work at 72 dpi.

Dot pitch is the most important specification for a display monitor, and is measured in millimeters (mm). It is a measurement that indicates the diagonal distance between like-colored phosphor dots on a display monitors. Dot pitch determines the quality of display monitors. The lower the number means a sharper image. In a desktop monitors, common dot pitches are 0.31mm, 0.28mm, 0.27mm, 0.26mm and 0.25mm.

What is resolution in a printed image?

Most printed pictures are made up of very small dots, and the resolution of the image is given in dots per inch, dpi (1 inch = 25.4 mm). The more dots per inch, the better the quality of the image. Printed images range from 100 to 150 dpi for newspapers, to 300 dpi for good quality and 800 dpi for the highest quality printing.

Printers are rated by the maximum number of dpi which they can print. Good printers can work at 600 dpi. Each colored dot is made up of a mixture of cyan, magenta, yellow and black inks (CMYK standard).

For most purposes, pixels and dots, and ppi and dpi are interchangeable concepts. But, it is useful to separate them when calculating how many pixels are needed to print a picture of a certain size with a printer of given dpi resolution.

What is resolution in a camera or scanner file?

Digital cameras are rated by the number of pixels they will record in one image file, typically in the range of two to six megapixels, and much higher for professional cameras. Scanners are rated by the number of dots per inch that they will record, so the file size depends on the size of the object scanned.

A high quality color picture file can have five million pixels or more, but the printer limits the number of pixels to what it can print in the space it is given.

The total number of pixels P in a picture is:

P = (dpi)2 x height (inches) x width (inches)

Information Processing > Resolution