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J277 1.2.4 Images

Part 2 of 5 · J277 1.2.4-1.2.5 · Data representation

Bitmap images as a grid of pixels, and the two properties examiners most often see confused.

Students will:

  • explain how pixels and binary codes represent an image
  • distinguish resolution from colour depth
  • explain how each affects quality and file size
  • define metadata and give suitable examples
  • calculate the size of an uncompressed image file

Inside: 6 explanation cells, 4 multiple-choice questions, 1 fill-in-the-blanks cell and 5 written answers. 32 marks, about 75 minutes.

Series: J277 1.2.4-1.2.5 · Data representation, part 2 of 5.

Shared by Coding PathwayVerified teacher

  • 16 cells
  • About 75 minutes
  • CC BY-SA 4.0
  • Shared 17 Aug 2026
  • Updated 9 Sept 2026

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The whole resource, exactly as a class sees it. Answers and marking are held back.

Data representation 2: images

A digital bitmap image is built from a grid of small picture elements called pixels. The colour of each pixel is represented by a binary code.

By the end of this worksheet, you should be able to:

  • explain how pixels and binary codes represent an image
  • distinguish resolution from colour depth
  • explain how each affects quality and file size
  • define metadata and give suitable examples
  • calculate the size of an uncompressed image file
  • interpret a small image when a code-to-colour mapping is provided

Work through the explanation, checks and applications in order. Use the final challenge to connect several ideas.

1. Pixels and binary codes

A pixel is the smallest individual picture element in a bitmap image. Each pixel has one colour, represented by a binary code.

The file contains the codes for the pixels and information needed to interpret the image. When the pixels are displayed in the correct order and colours, they form the complete image.

Increasing the size of a bitmap display without adding pixels can make individual pixels more visible. This is sometimes described as the image becoming pixelated.

Pixels, resolution and colour depth A four by four pixel image is represented by colour codes. A second view explains that resolution changes the number of pixels, while colour depth changes the number of bits available for each pixel colour. A bitmap is a grid of pixels resolution: 4 × 4 = 16 pixels Higher resolutionmore pixels can represent more detailand create more pixel codes to store Higher colour depthmore bits per pixel provide more possible coloursbut do not add more pixels
Fill in the blanks4 marks
A bitmap image is a grid of label 1. Each pixel has a particular label 2 represented by a label 3. The complete image appears when the pixels are displayed in the correct label 4.
  • order
  • binary code
  • sample rate
  • pixels
  • character set
  • colour
Written answer4 marks

Describe how a bitmap image is represented in a computer.

Use the terms grid, pixel, colour and binary code.

Students type their answer here.

2. Resolution and colour depth

Resolution is the number of pixels in an image, commonly described using width × height.

  • Higher resolution means more pixels.
  • More pixels can capture more detail.
  • More pixels increase the file size.

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

  • Higher colour depth provides more possible colour codes.
  • More colours can produce smoother or more accurate colour.
  • More bits per pixel increase the file size.

Colour depth does not increase the number of pixels. Resolution does not increase the number of bits used for each pixel.

Multiple choice, several answers2 marks

Which two statements are accurate? Select both.

  • AIncreasing colour depth directly increases the number of pixels
  • BIncreasing resolution increases the number of pixels and usually the file size
  • CIncreasing resolution reduces the amount of image data
  • DIncreasing colour depth increases the number of possible colours and usually the file size
Multiple choice1 mark

What is the maximum number of different colours available with a colour depth of 4 bits?

  • A4
  • B8
  • C16
  • D32
Multiple choice1 mark

An image palette must represent 180 different colours. What is the minimum colour depth that can provide enough distinct binary codes?

  • A180 bits
  • B8 bits
  • C256 bits
  • D7 bits

3. Image metadata

Metadata is additional data about a file. Image metadata may include:

  • width and height in pixels
  • colour depth
  • date and time created
  • geographical location
  • author or device information
  • file type

Metadata is not the collection of codes that gives every pixel its colour. Those codes are the image data. Metadata describes the image or helps software interpret it.

Written answer4 marks

Define metadata and give three suitable examples of metadata for a digital image.

Use precise examples such as width or date created, rather than writing only colour or size.

Students type their answer here.

4. Image-file size

For a simple uncompressed image:

file size in bits = width in pixels × height in pixels × colour depth

Example:

An image is 100 pixels wide, 80 pixels high and has a colour depth of 4 bits.

100 × 80 × 4 = 32,000 bits

32,000 ÷ 8 = 4,000 bytes

Always multiply by the colour depth, not by the number of colours available.

Written answer5 marks

An uncompressed image is 200 pixels wide and 150 pixels high. It has a colour depth of 8 bits. Calculate its file size in bits, bytes and kilobytes. Use 1 KB = 1,000 bytes and show your working.

Multiply width, height and colour depth. Then divide by 8 and by 1,000.

Students type their answer here.

Multiple choice1 mark

A four-pixel row uses this mapping: 00 = black, 01 = white, 10 = red, 11 = blue. Which colours are represented by 00 10 10 01?

  • AWhite, red, red, black
  • BBlack, red, red, white
  • CRed, black, black, blue
  • DBlack, blue, blue, white
Written answer4 marks

A photographer doubles the width and height of an image while keeping the colour depth unchanged. Explain the likely effects on image quality and file size.

Consider what happens to the total number of pixels. Width and height both change.

Students type their answer here.

Written answer6 marks

Challenge: a student says, “Increasing colour depth improves an image because it adds more pixels.” Evaluate and correct the statement.

Separate the effect of colour depth from resolution, then discuss quality and file size.

Students type their answer here.

Closed-book review

  1. What is a pixel?
  2. How is a pixel's colour represented?
  3. What is resolution?
  4. What is colour depth?
  5. How does each affect quality?
  6. How does each affect file size?
  7. What is metadata? Give three examples.
  8. Write the image-file size formula.

Final check: colour depth controls possible colours, while resolution controls the number of pixels.