Dots and pixels

The terms dots and pixels are sometimes used interchangeably, but in fact they refer to two different, although related, things.

When a screen or monitor displays an image it uses coloured pixels. Each of these pixels is made up of a red, green and blue dot. By varying the brightness of each of these dots, different coloured pixels can be created. To find out the number of dots that are used on a particular screen, you need to multiply the pixel count by three. Inversely, to find the number of pixels, divide the number of dots by three.

Typically, computer monitors have a resolution of between 60ppi and 100ppi (pixels per inch), but for printing, images should be 300ppi for photographic resolution.

In printing, the term ‘dots’ refers to the small droplets of ink that a printer can lay on a sheet of paper, but a printer requires many more than 300 small droplets of ink per inch to make up an image. While the brightness of dots on a screen can be changed to render a particular colour pixel, the brightness of ink in a printer cannot be changed.

A printer therefore has to use many tiny cyan, magenta, yellow and black dots to reproduce a particular coloured pixel, for example, the Epson Stylus Photo R2880 prints at 5760x1440 dpi.

Manufacturers also add more inks of different colours to their printers. This allows for a wider range of colours to be produced (this range is called a ‘colour gamut’), which makes prints more faithful to the original image.

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