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AQA 8525 GCSE Computer Science · 3.3 Fundamentals of Data Representation

Stretch tasks Representing Images

Task 1

Quiz Challenge

A quiz game against four computer players, then short and long written answers.

  1. Quiz Blitz12 questions against the clock
  2. Quick Fire4 short answers
  3. Big Think2 long answers

About 20 minutes

Task 2

This or That

Pixel the cat asks 8 questions. Each has two answers: pick the right one.

  • Two answers to every question
  • A fish treat for every right answer
  • Streaks win Pixel shades, then a party hat

About 4 minutes

Task 3

Memory Match

Flip the cards two at a time to match each term card to its meaning card.

  • 12 cards: each term has a meaning
  • One peek at every card
  • Combo points for pairs found in a row

6 pairs, about 4 minutes

Task 4

Sort It

Sort each statement into the right box, like the tick-box tables in the exam.

  • 10 cards to sort into 2 boxes
  • Drag a card, tap a box or press its number
  • Combo points for cards sorted in a row

10 cards, about 4 minutes

The games need JavaScript. Every question is below, with the answers at the end.

Read the lesson: Representing Images

Representing Images: the questions

Quiz Challenge, round 1: Quiz Blitz

  1. What is a bitmap image?

    • A map of a city
    • A compressed photograph
    • A grid of pixels, with a colour value for each
    • An image made of shapes and lines

  2. How many pixels are in a 1920 by 1080 image?

  3. How many colours does an 8-bit colour depth give?

  4. In 24-bit colour, how many bits does each of red, green and blue get?

    • 3
    • 16
    • 8
    • 24

  5. The same 1920 by 1080 image has more pixels on a bigger screen.

    • True
    • False

  6. Which metadata does software need to rebuild the grid of pixels?

    • The location
    • The width
    • The date taken
    • The camera model

  7. Which formula gives an image's file size in bits?

    • width x height x colour depth
    • width + height + colour depth
    • width x height
    • colour depth x 8

  8. An image is 800 x 600 with 24-bit colour. What is its size in kB, using AQA's 1000?

  9. Which TWO privacy risks can image metadata carry?

    Tick 2.

    • The number of pixels
    • The exact location a photo was taken
    • The time it was taken
    • The colour of each pixel
    • The image's width

  10. What is true colour?

    • 1-bit colour
    • 8-bit colour
    • Colour with no metadata
    • 24-bit colour, about 16.7 million colours

  11. Adding one bit of colour depth adds one bit to every pixel in the image.

    • True
    • False

  12. Doubling the width and the height of an image makes the file...

    • Eight times bigger
    • The same size
    • Four times bigger
    • Twice as big

Quiz Challenge, round 2: Quick Fire

  1. Explain the difference between resolution and colour depth. [2 marks]

  2. Explain why software cannot display an image without knowing its width. [2 marks]

  3. Explain why photographs taken on a phone can be a privacy risk. [2 marks]

  4. Explain how 24-bit colour gives about 16.7 million colours. [2 marks]

Quiz Challenge, round 3: Big Think

  1. An image is 800 by 600 pixels with a colour depth of 24 bits. Calculate its size in megabytes, showing every step. [4 marks]

  2. Explain how resolution, colour depth and metadata each affect an image file. [6 marks]

This or That: tick the right answer

  1. Which gives more colours?

    • 24-bit colour
    • 8-bit colour

  2. A 4-bit colour depth gives how many colours?

    • 16
    • 4

  3. Is resolution the size of an image on the screen?

    • No: it is a count of pixels
    • Yes: it is measured in centimetres

  4. Metadata is given in bytes. When do you add it?

    • Before multiplying anything
    • Once the image data is in bytes

  5. Why are raw images so large?

    • Every pixel needs its own colour value
    • Metadata is huge

  6. How many levels does each channel have in 24-bit colour?

    • 256
    • 24

  7. Which of these is metadata?

    • The colour of the first pixel
    • The image's width

  8. A higher colour depth means...

    • More bits per pixel
    • More pixels

Memory Match: match each term to its meaning

TermMeaning
A Pixel1 A grid of pixels
B Resolution2 Bits per pixel
C Colour depth3 24-bit colour
D Metadata4 One colour value in a bitmap's grid
E True colour5 Data about the file itself
F Bitmap6 Width x height, in pixels

Sort It: tick one box in each row

Is each part of an image file pixel data or metadata?

StatementPixel dataMetadata
The GPS location
The colour of the top-left pixel
The red, green and blue values of each pixel
The binary values for every pixel
The camera settings
The date the photo was taken
The width in pixels
The colour depth
Most of the file's size
The height in pixels
Answers

Round 1: Quiz Blitz

  1. A grid of pixels, with a colour value for each The file is a map of which bits belong to which position in the grid.
  2. 2073600 1920 x 1080 = 2,073,600.
  3. 256 2 to the power 8 is 256.
  4. 8 8 + 8 + 8 = 24, so each channel has 256 levels.
  5. False Resolution is a count. Only the size each pixel appears changes.
  6. The width The width shows where each row ends.
  7. width x height x colour depth Every pixel needs colour-depth bits.
  8. 1440 800 x 600 x 24 = 11,520,000 bits = 1,440,000 bytes = 1440 kB.
  9. The exact location a photo was taken; The time it was taken Phones commonly record location and time, which travel with the file.
  10. 24-bit colour, about 16.7 million colours 256 x 256 x 256 = 16,777,216.
  11. True That is why higher colour depths make files so much bigger.
  12. Four times bigger Twice as wide and twice as tall is four times the pixels.

Round 2: Quick Fire

    • Resolution is the number of pixels, width by height
    • Colour depth is the number of bits for each pixel's colour
    Model answer

    Resolution is the number of pixels in the image, given as width by height. Colour depth is the number of bits used to store the colour of each pixel.

    • The colour values are stored as one long list
    • The width shows where each row ends, so the rectangle can be rebuilt
    Model answer

    The colour values are stored as one long list. The width shows where each row ends, so without it the software cannot rebuild the list into a rectangle of pixels.

    • Their metadata records the location and time
    • Which travels with the file when it is shared
    Model answer

    A phone usually records the exact location and time in the photo's metadata, and that information travels with the file whenever it is shared.

    • 8 bits each for red, green and blue
    • 256 x 256 x 256 = 16,777,216
    Model answer

    24-bit colour gives 8 bits each to red, green and blue, so each channel has 256 levels, and 256 x 256 x 256 = 16,777,216 colours.

Round 3: Big Think

    • 800 x 600 = 480,000 pixels
    • x 24 = 11,520,000 bits
    • / 8 = 1,440,000 bytes
    • / 1000 / 1000 = 1.44 MB
    Model answer

    Pixels = 800 x 600 = 480,000. Bits = 480,000 x 24 = 11,520,000. Bytes = 11,520,000 / 8 = 1,440,000. kB = 1,440,000 / 1000 = 1440. MB = 1440 / 1000 = 1.44 MB.

    • More pixels give more detail
    • More pixels mean proportionally more data
    • Colour depth decides how many colours: n bits give 2 to the power n
    • More bits per pixel make the file bigger
    • Metadata holds the width, height and colour depth needed to rebuild the image
    • Metadata adds a little to the size, and can carry private details
    Model answer

    Resolution is the number of pixels: more pixels give more detail, but every pixel needs its own colour value, so the file grows in proportion, and doubling the width and height makes it four times bigger. Colour depth decides how many colours each pixel can be, since n bits give 2 to the power n colours; more bits per pixel make the whole file bigger. Metadata stores the width, height and colour depth that software needs to rebuild the image. It adds a small amount to the file size, and it can also carry private details such as the location.

This or That

  1. 24-bit colour 24 bits give over 16 million colours. 8 bits give 256.
  2. 16 2 to the power 4 is 16.
  3. No: it is a count of pixels The same image can fill a wall or a phone.
  4. Once the image data is in bytes Add values only when they are in the same unit.
  5. Every pixel needs its own colour value Millions of pixels, each with up to 24 bits.
  6. 256 8 bits per channel give 256 levels.
  7. The image's width Pixel colours are the image data. The width describes the file.
  8. More bits per pixel Resolution is the number of pixels. Colour depth is bits per pixel.

Memory Match

  • A 4 Pixel: One colour value in a bitmap's grid
  • B 6 Resolution: Width x height, in pixels
  • C 2 Colour depth: Bits per pixel
  • D 5 Metadata: Data about the file itself
  • E 3 True colour: 24-bit colour
  • F 1 Bitmap: A grid of pixels

Sort It

  1. Metadata The GPS location A privacy risk that travels with the file.
  2. Pixel data The colour of the top-left pixel Each pixel's colour value is the image data itself.
  3. Pixel data The red, green and blue values of each pixel In true colour, each pixel stores three channels.
  4. Pixel data The binary values for every pixel That is the bitmap.
  5. Metadata The camera settings Recorded by the camera alongside the pixels.
  6. Metadata The date the photo was taken Data about the file, not a pixel.
  7. Metadata The width in pixels It tells software where each row ends.
  8. Metadata The colour depth It tells software how many bits belong to each pixel.
  9. Pixel data Most of the file's size Millions of pixel values dwarf the metadata.
  10. Metadata The height in pixels Part of the data about the file.