A Level Computer Science: Multimedia (Graphics and Sound) — Practice Questions (Cambridge 9618)

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs — examination boards hold copyright in their own papers. Use these alongside the official past papers available free from your board.

Related: Information Representation study guide · Information Representation revision notes

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What do these questions practise? Section 1.2 Multimedia of the Cambridge International AS & A Level Computer Science 9618 syllabus (2027–2029): how bitmap images and vector graphics are encoded, estimating bitmap file sizes, the effect of resolution and colour depth, choosing bitmap or vector for a task, how sound is sampled and encoded, and the effect of sampling rate and resolution on file size and accuracy.

Section A: graphics

1. Define the terms pixel, image resolution and colour depth. [3]

2. State what is stored in the file header of a bitmap image file, giving two examples. [2]

3. A bitmap image is 800 pixels wide and 600 pixels high with a colour depth of 8 bits. (a) State how many different colours each pixel can represent. [1] (b) Calculate the file size in kibibytes (KiB), ignoring the header. Show your working. [3]

4. A photograph is 1920 × 1080 pixels with a colour depth of 24 bits. Estimate the file size in mebibytes (MiB), ignoring the header. [3]

5. Explain the effect on image quality and file size of reducing the colour depth of a bitmap from 24 bits to 8 bits. [3]

6. Explain how a vector graphic is encoded. Use the terms drawing object, property and drawing list. [3]

7. Justify whether a bitmap or a vector graphic is more suitable for: (a) a company logo that will be printed on business cards and on large banners; [2] (b) a photograph of a landscape. [2]

8. Explain the difference between image resolution and screen resolution. [2]

Section B: sound

9. Explain how analogue sound is converted into digital data. Use the terms sampling, sampling rate and sampling resolution. [4]

10. A stereo recording (2 channels) lasts 30 seconds, sampled at 44 100 Hz with a sampling resolution of 16 bits. Calculate the file size in bytes and estimate it in MiB. [3]

11. Explain the impact of increasing the sampling rate on the accuracy of a recording and on the file size. [3]

12. A voice message app records mono audio at 22 050 Hz with 8-bit resolution. Explain one reason why these settings may be chosen, and one drawback. [2]

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Answers

1. Pixel: the smallest addressable element of a bitmap image [1]. Image resolution: the number of pixels in the image, given as width × height [1]. Colour depth (bit depth): the number of bits used to represent the colour of each pixel [1].

2. Data about the image needed to display it [1]; any two of: width and height in pixels, colour depth, file type, compression used, file size [1].

3. (a) 2⁸ = 256 colours [1]. (b) 800 × 600 = 480 000 pixels [1]; × 8 bits = 3 840 000 bits = 480 000 bytes [1]; 480 000 ÷ 1024 = 468.75 KiB [1].

4. 1920 × 1080 × 24 = 49 766 400 bits [1] = 6 220 800 bytes [1]; ÷ 1024 ÷ 1024 ≈ 5.93 MiB [1].

5. Fewer bits per pixel means fewer possible colours (from about 16.7 million to 256) [1], so colours may show banding and the image is less true to life [1]; the file size is reduced to one third of the original, because each pixel uses 8 bits instead of 24 [1].

6. A vector graphic is stored as a drawing list [1] of drawing objects, such as lines, circles and rectangles [1]; each object is described by properties, such as coordinates, radius, line colour, line width and fill colour, from which the image is redrawn when displayed [1].

7. (a) Vector [1]: it can be scaled to any size without losing quality or becoming pixelated, and a simple logo needs few objects, so the file is small [1]. (b) Bitmap [1]: a photograph has continuous variations of colour that cannot be described efficiently by drawing objects, so each pixel’s colour is stored [1].

8. Image resolution is the number of pixels in the image itself [1]; screen resolution is the number of pixels the display can show horizontally and vertically, so an image larger than the screen resolution must be scaled or scrolled [1].

9. The amplitude of the analogue sound wave is measured at regular intervals (sampling) [1]; the sampling rate is the number of samples taken per second [1]; each sample is stored as a binary number [1]; the sampling resolution is the number of bits used for each sample, which sets how precisely the amplitude is recorded [1].

10. 44 100 × 16 × 2 × 30 = 42 336 000 bits [1] = 5 292 000 bytes [1] ≈ 5.05 MiB [1].

11. More samples per second capture the wave’s changes more closely, so the digital recording is a more accurate reproduction of the original [1–2]; more samples must be stored, so the file size increases in proportion to the sampling rate [1].

12. Reason: speech needs less detail than music, so lower settings still sound clear and give a small file that uploads quickly [1]. Drawback: lower accuracy, so higher frequencies are lost and the sound may be less natural or noisier [1].

Frequently asked questions

Should I use 1000 or 1024 for file sizes? The 9618 syllabus uses binary prefixes: kibibyte (1024 bytes) and mebibyte (1024 × 1024 bytes). Show your working so method marks are available.

Do I need to include the header in calculations? Questions usually say to ignore it; the calculation estimates the size of the pixel data only.

Based on the Cambridge International AS & A Level Computer Science 9618 syllabus for 2027, 2028 and 2029, section 1.2 Multimedia.