Complete GCSE Computer Science lesson on bitmap images, colour depth, file-size calculations and compression, with worksheets and answers.
Pupils begin by decoding an 8 × 8 binary image and calculating its memory requirement in bits and bytes. They compare bitmap and vector graphics before exploring resolution, metadata and how colour depth determines the number of available colours.
The lesson then introduces the formula:
Uncompressed image size = width × height × colour depth
Pupils complete supported calculations using 1-bit, 2-bit, 4-bit, 8-bit and 24-bit colour.
The compression activities introduce lossless compression and run-length encoding. Pupils encode and decode pixel rows, investigate when RLE reduces file size and construct an example where RLE becomes inefficient.
Pupils also compare lossy and lossless compression and consider appropriate uses for PNG, JPEG, GIF and SVG formats.
This resource contains:
Approximately 70-minute lesson plan
Learning objectives and success criteria
Teaching sequence and suggested timings
Key vocabulary and common misconceptions
Binary mystery-image starter
Bitmap vocabulary matching cards
Visual colour-depth reference sheet
Printable 8 × 8 pixel-design activity
Binary pixel-encoding exercise
Run-length encoding investigation
Lossy and lossless compression scenarios
Scaffolded GCSE examination questions
Answers and marking guidance
The complete lesson can be delivered from the printable pack. It requires no external websites, videos or student accounts.
Suitable for GCSE Computer Science and higher-attaining Key Stage 3 classes.