Lesson 4 - Exam practice
Test your knowledge
Work through these questions as you would in an exam. Answer the MCQ first, then write your answers to the written questions before revealing the mark scheme.
Section 1: Multiple choice
Select one answer per question. Instant feedback appears when you choose.
Question 1 of 5
An image is 400 pixels wide and 300 pixels tall with a colour depth of 8 bits. What is the uncompressed file size in bytes?
400 × 300 = 120,000 pixels. 120,000 × 8 bits = 960,000 bits. 960,000 ÷ 8 = 120,000 bytes.
Question 2 of 5
A colour depth of 16 bits per pixel allows how many different colours?
Number of colours = 2^colour_depth = 2¹&sup6; = 65,536.
Question 3 of 5
Which change would reduce the file size of a bitmap image by exactly half?
File size = Width × Height × Colour depth. Halving both dimensions multiplies by 0.5 × 0.5 = 0.25. Halving width alone gives 0.5. Reducing depth by one bit does not halve -- it divides by 2 only if halving the depth value.
Question 4 of 5
Which statement about vector graphics is correct?
Vector graphics store shapes as mathematical equations (lines, curves, coordinates). This means they can be scaled to any size without quality loss, unlike bitmap images.
Question 5 of 5
A bitmap image uses 24-bit true colour. How many bytes are used to store the colour of a single pixel?
24 bits ÷ 8 = 3 bytes per pixel. This is why 24-bit colour is sometimes called '3 bytes per pixel' or 'RGB with one byte per channel.'
Section 2: Written questions
Write a full answer in your notebook or on paper before checking against the lesson notes.
Written question 1
Calculate the uncompressed file size of a 1280 × 720 pixel image with a colour depth of 24 bits. Give your answer in kilobytes (KB). Show all working.
4 marks
Written question 2
A designer has a bitmap image and a vector version of the same logo. Describe two differences between these formats and explain one advantage of each.
4 marks
Written question 3
Explain why increasing the colour depth of an image improves its quality but also increases its file size. Use the file size formula in your answer.
4 marks