OCR GCSE Computer Science (J277) · Computer systems (Paper 1) › Memory and storage › Data storage
Practise Images. 12 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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An image is 4 pixels wide and 5 pixels high, with a colour depth of 2 bits. Calculate the file size of the image in bits.
40 bits
State how many different colours can be represented using 1 bit.
2
Sample questions
Written for this site in the style of OCR exam questions. They are not taken from real past papers.
Question 1Easy3 marks
(a) State what is meant by a pixel.[1]
(b) State what is meant by colour depth.[1]
(c) State what is meant by the resolution of an image.[1]
Show the answer and mark scheme
(a)
a single point / the smallest element of colour in an image
(b)
the number of bits used to store the colour of each pixel
(c)
the number of pixels in the image (width × height) / the number of pixels per inch
Question 2Medium4 marks
(a) Explain what metadata is and why it is stored with an image file.[2]
(b) Give two examples of metadata, other than width and height, that could be stored with a digital photo.[2]
Show the answer and mark scheme
(a)
data about the image, e.g. its width, height and colour depth
so the computer knows how to display / reconstruct the image correctly, e.g. how many pixels are in each row and how many bits each pixel uses
(b)
colour depth
date / time taken
location / GPS coordinates
camera make / model / settings
file type / format
file size
author / copyright information
Question 3Hard5 marks
An image uses a colour depth of 2 bits, with this key: 00 = white, 01 = light grey, 10 = dark grey, 11 = black. The image is 6 pixels wide and 6 pixels high. The first row of the image is stored as: 00 01 11 11 10 00
(a) State the colour of each pixel in the first row, from left to right.[2]
(b) Calculate the file size of the whole image in bits. Ignore any metadata.[1]
(c) The artist wants to use two more colours, making six colours in total. Explain the effect on the colour depth and on the file size.[2]
Show the answer and mark scheme
(a)Answer: white, light grey, black, black, dark grey, white
first three: white, light grey, black
last three: black, dark grey, white
(b)Answer: 72 bits
6 × 6 × 2 = 72 (bits)
(c)
the colour depth must increase to 3 bits (2 bits only gives 4 colours)