Pixels determine the image size on a screen

Digital images are formed from lots (tens of millions in some cases) of different coloured dots, known as pixels. The pixels are tiny and tightly packed, so when viewed on a screen, the individual dots are not noticeable, giving the illusion of a perfectly smooth yet sharp image.

It so happens that computer screens are made up of pixels too, so it is reasonably easy to predict how much space an image will take up on a screen.

Example

Let’s use this picture of Archie. This is one of our free downloads, and is 300 pixels wide x 400 pixels high.

If we imagine a computer monitor that is 1300 pixels wide x 800 pixels high, this picture will take up this amount of space on the screen:

And here is our “medium” sized picture of Archie which is 480 pixels x 640 pixels:

See how this image takes up more space on the screen:

And what about our “high resolution” version of this image (3024 pixels x 4032 pixels)?

As you can see, the high resolution image is much bigger than this computer screen. So does this mean that you never need high resolution images for screen use? In many cases, that is correct, one of the smaller versions is likely to suffice. However if you were using an image for a full screen background, you may well need the high resolution version, but might want to reduce its size yourself.