AS · Practice questions · Bitmap and vector graphics

Grids and shapes.

Six original Cambridge-style questions on bitmap and vector graphics, with worked solutions.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Pixels times bits.

File size: width × height × colour depth bits; ÷ 8 for bytes, ÷ 1024 for KiB.
Colour depth: n bits give 2ⁿ colours; find the smallest n that is enough.
Vector: drawing list of drawing objects, each with properties; scales without pixelation.
Justify: bitmap for photographs; vector for logos, diagrams and anything resized often.

Recall

[3 marks]

Define the terms pixel, image resolution and colour depth.

Pixel: the smallest addressable element of a bitmap image, with one colour. ✓
Image resolution: the number of pixels in the image (width × height). ✓
Colour depth: the number of bits used to represent the colour of each pixel. ✓

Calculate

[3 marks]

A bitmap is 2048 pixels wide and 1536 pixels high, with a colour depth of 16 bits. Estimate its file size in MiB. Show your working.

2048 × 1536 = 3 145 728 pixels. ✓
× 2 bytes = 6 291 456 bytes. ✓
6 291 456 ÷ 1 048 576 = 6 MiB. ✓

Explain

[2 marks]

Explain the effect of increasing the colour depth of a bitmap image on its quality and on its file size.

More colours can be represented, so colours are more accurate / gradients are smoother. ✓
More bits are stored per pixel, so the file size increases (in proportion to the colour depth). ✓

Explain

[3 marks]

Describe how a vector graphic is encoded.

It is stored as a drawing list (a list of commands). ✓
Each item is a drawing object, such as a line, circle or rectangle. ✓
Each object has properties, e.g. coordinates, radius, line colour, line width, fill colour. ✓

Apply

[4 marks]

A school needs (a) a photograph of its sports team for its website and (b) its crest, which will be printed on letters, shirts and a large banner. Justify whether each should be a bitmap or a vector graphic.

(a) Bitmap. ✓
A photograph has many complex colour changes that cannot be described by simple shapes. ✓
(b) Vector. ✓
The crest is made of shapes and can be scaled to any size without losing quality / becoming pixelated. ✓

Calculate

[3 marks]

A 1200 × 800 pixel image must be able to show at least 200 different colours. Calculate the minimum colour depth and the estimated file size in KiB.

2⁷ = 128 is too few and 2⁸ = 256 is enough, so 8 bits. ✓
1200 × 800 = 960 000 pixels × 1 byte = 960 000 bytes. ✓
960 000 ÷ 1024 = 937.5 KiB. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.