Pixels, colour depth, resolution, sample rate, bit depth. File size calculations appear in every paper — must be able to do these.
| Term | Definition |
|---|---|
| Pixel | |
| Colour depth | |
| Resolution |
Image file size formula: width (pixels) × height (pixels) × colour depth (bits) ÷ 8 = bytes. Example: 1028 × 640 pixels, 15-bit colour: (1028 × 640 × 15) ÷ (8 × 1024 × 1024) megabytes. Jun 2022 Q3(d)(ii): full file size calculation — must show all working.
| Term | Definition |
|---|---|
| Sample rate | |
| Bit depth |
Sound file size formula: sample rate (Hz) × bit depth (bits) × duration (seconds) ÷ 8 = bytes. Jun 2024 Q2(b): "the time between samples" = sample interval (NOT sample rate definition). Jun 2023 Q5(e)(ii): image file size with metadata: (100 × 600 × 32) ÷ 8 + 1024.
| Point | Detail |
|---|---|
| Colour channel encoding | |
| Example | |
| 24-bit (true colour) | |
| Bit depth scale |
A bitmap image is stored with 1 bit per pixel. What colours can it represent?
An image is 1028 × 640 pixels with a colour depth of 15 bits. Calculate the file size in megabytes. Show all working. (3 marks)
A sound recording has a sample rate of 44,100 Hz, a bit depth of 16 bits, and lasts 3 minutes. Calculate the file size in megabytes. Show all working. (3 marks)