How Computers Represent Images

Computers store images using binary numbers (0s and 1s).

An image on a computer screen is made up of thousands or millions of tiny squares called pixels.

Each pixel stores information about colour.

The computer converts this information into binary data so the image can be stored and displayed.

What Is a Pixel?

A pixel (short for picture element) is the smallest unit of an image displayed on a screen.

Each pixel represents one colour value.

When many pixels are combined together, they form a complete image.

Example:

A small image might contain:

100 × 100 pixels

This means the image contains 10,000 pixels.

What Is Resolution?

Resolution refers to the number of pixels in an image.

It is usually written as:

width × height

Example:

1920 × 1080

This means:

• 1920 pixels across

• 1080 pixels down

Higher resolution means:

• More pixels

• More detail

• Better image quality

However, higher resolution also means larger file size.

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What Is Colour Depth?

Colour depth refers to the number of bits used to represent the colour of each pixel.

The more bits used, the more colours can be displayed.

Example:

Colour DepthNumber of Colours1 bit2 colours8 bits256 colours24 bits16.7 million colours

Higher colour depth means:

• More realistic images

• Greater file size

Factors Affecting Image File Size

The file size of an image depends on:

1️⃣ Resolution

2️⃣ Colour depth

Higher values for these will increase the file size.

Example:

• High resolution + high colour depth → large file size

• Low resolution + low colour depth → smaller file size

Example

An image with:

1000 × 1000 pixels
24-bit colour depth

contains:

• 1,000,000 pixels

• Each pixel uses 24 bits

This results in a large image file.

Why Image Representation Is Important

Understanding image representation helps students learn:

• How images are stored in computers

• Why image files have different sizes

• How image quality changes

This knowledge is important in areas such as:

• Digital photography

• Graphic design

• Web development

Exam Tip (2210 / 0478)

Students are often asked to:

• Define pixel

• Define resolution

• Define colour depth

• Explain how these affect image quality and file size

Always remember:

• More pixels = higher resolution

• More bits = more colours

Practice Question

Explain one factor that increases image file size.

Answer

Increasing the resolution increases the number of pixels in an image, which increases the file size.

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