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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: 4 text sections, 2 multiple-choice activities, 5 completion activities, 4 written answers. 18 marks. Suggested teaching time: 40–60 minutes. 1 diagram.

Includes a teacher guide with suggested sections, timings and common misconceptions.

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

Shared by Coding PathwayVerified teacher

  • 15 cells
  • About 45 minutes
  • CC BY-SA 4.0
  • Shared 17 Aug 2026
  • Updated 27 Oct 2026

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

Images

A bitmap is a grid of pixels. Each pixel is one small picture element with one colour at a time. Its colour is represented by a binary code. Read the six-pixel example before using these ideas in a larger image.

A six-pixel bitmap and its colour codes A three-column, two-row grid contains black, white, black on the top row and white, black, white below. Zero represents black and one represents white. There are six pixels, each with one colour. A 3 × 2 bitmap 0 1 0 1 0 1 0 = black · 1 = white 6 pixels, with 1 bit for each pixel Each pixel has one colour at a time.
Fill in the blanks3 marks
A bitmap is a grid of Answer 1. Each pixel has one Answer 2 represented by a Answer 3.
  • pixels
  • colour
  • binary code
  • sound sample
Written answer2 marks

Describe how a bitmap image is represented in a computer.

Students type their answer here.

1. Two different changes

CharacteristicMeaningPossible effect of increasing it
ResolutionNumber of pixels, often width × height.More detail can be captured; more pixel data must be stored.
Colour depthBits used for each pixel's colour.More possible colours and smoother colour changes; more bits must be stored per pixel.

Colour depth does not add pixels. Resolution does not change bits per pixel.

With 4 bits per pixel there are 2⁴ = 16 possible colours. With 7 bits there are 128; with 8 bits there are 256. Choose the smallest depth that provides enough codes.

Multiple choice1 mark

An image is captured using more bits per pixel but the same width and height. What changes?

  • AThe image automatically has more pixels
  • BThere are more possible colours, with more data per pixel
  • CEach pixel must show several colours at once
  • DThe uncompressed pixel data must become smaller
Fill in the blanks1 mark
An image needs 180 different colours. The minimum colour depth is Answer 1 bits per pixel.

2. Information about the image

Metadata is data about the image or file. It may include dimensions, colour depth, date/time created, file type, creator or location.

The binary colour codes for individual pixels are image data, not metadata. Some metadata helps software interpret that data.

Written answer2 marks

An image file already includes its width and height. State two other items of image metadata.

Students type their answer here.

3. Calculate uncompressed pixel data

Bits = width × height × colour depth. Divide by 8 for bytes, then by 1,000 for KB when that conversion is stated.

For a 100 × 80 image at 4 bits per pixel: 100 × 80 × 4 = 32,000 bits, then 32,000 ÷ 8 = 4,000 bytes.

Now use 200 × 150 pixels at 8 bits per pixel. Ignore metadata and headers; use 1 KB = 1,000 bytes.

Written answer2 marks

Show your method for calculating the 200 × 150 image's pixel-data size in KB.

Students type their answer here.

Fill in the blanks1 mark
The final size of this image's uncompressed pixel data is Answer 1 KB.
Fill in the blanks2 marks
Use the diagram's mapping, 0 = black and 1 = white. A new two-pixel row has codes 1 0. (a) Left pixel: Answer 1 (b) Right pixel: Answer 2
Written answer2 marks

A camera captures a scene at 400 × 300 pixels instead of 200 × 150 pixels. Explain why the new capture may record more detail.

Students type their answer here.

Fill in the blanks1 mark
The new 400 × 300 capture uses the same colour depth as the 200 × 150 capture. Its uncompressed pixel data is Answer 1 times the original size.
Multiple choice1 mark

Which item is metadata rather than an individual pixel's image data?

  • AThe binary colour code for pixel 1
  • BThe binary colour code for pixel 2
  • CThe date the image was created
  • DThe ordered colour code of every pixel