Image sensors - Image resolution

Unlike conventional photographs where we refer to a 5 x 7-inch or 8 x 10-inch print, the overall size of a digital image is measured in pixels. They are grouped in a matrix of coloured dots. The density of this matrix determines the amount of detail the image can show. This is known as resolution.

Pixel dimensions for digicams may range from  2400 x 1800 or higher to  resolutions as low as 800 x 600 or even 640 x 480.

This figure tells us the height and width of the recorded image. It determines what an image will look like in terms of quality, depending on the output required. As a general rule, the more pixels there are the greater the level of detail captured.

To avoid creating larger than necessary files on your memory card or computer, it is important to determine beforehand what the image will be used for, as this can tell us what resolution we will need.

Required pixel dimensions can be calculated by multiplying the print size by the resolution, so an 8 x 10 inch print at 300 dpi (magazine quality) requires a resolution of 2400 x 3000. An inkjet print will generally require between 170 and 250 dpi, while if the image is meant for web use resolutions of 72 ppi should be satisfactory.