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Digital images can be made by putting together lots of tiny squares, known as pixels - short for picture element.

When an image is digitised to be stored on a computer, it's turned into a set of pixels.

Imagine an avatar you have made with a square grid placed over it.

Every one of the squares is a pixel.

To store the image, the computer records a number to represent the colour of each square. It works a bit like a digital colour by numbers!

The more squares in the grid, the better the images will look, as more pixels are used to represent the image.

If you look closely at a computer screen, you will see that it is made up of millions of tiny squares.

Each one of those squares is a pixel.

To display an image, the computer tells the screen to show a particular colour for each of the pixels.

Images made up of pixels can be saved as a file using a number of formats.

Different file types all use pixels in some way to store the image. These include:

• JPEG
• TIFF
• PNG
• GIF
• BMP - short for bitmap

A bitmap is a method for storing images using pixels. It is called a bitmap because it is a map of where the bits of information are stored. The information is stored as a sequence of numbers for each pixel's colour.

In a simple black and white image, a bitmap just needs to know if a pixel is on or off which can be stored as a 1 or 0.

In a colour image, we need lots of bits (typically 24) to store the colour values of each pixel. An image could contain around 16.8 million different colours.

Not all images use pixels.

Vector graphics are made up of lines, curves and shapes instead of pixels.

Each part of a vector graphic is known as an object. It is editable and can easily be changed.

Vector graphics are great for creating diagrams or graphics, as each object is stored using an algorithm to make smooth lines.

This means that if you make a change to an object, such as resizing it, the quality of the image doesn't change.

Raster graphics (bitmaps) are made up of a collection of pixels. Resizing them can affect the quality of the image. Photographs are usually always raster images.

Vector graphic applications have lots of different ways to work with objects.