Image Representation — Bitmaps, Resolution & Colour Depth
Learn how digital images are stored as bitmaps using pixels, resolution, and colour depth, and how to calculate file sizes.
📚 Learning Steps
💡 Study Tips
- • Read through at your own pace
- • Try the interactive simulators hands-on
- • Study the pseudocode — it appears in exams
- • Quiz yourself before moving on
Step 1: How Are Digital Images Stored?
📖 TheoryA bitmap image is made up of a grid of tiny squares called pixels (picture elements). Each pixel stores a single colour value as a binary number.
The two key properties of a bitmap are:
1. Resolution — the number of pixels in the image
•Measured as width × height (e.g., 1920 × 1080)
•Higher resolution = more pixels = more detail = larger file
2. Colour depth — the number of bits used to store each pixel's colour
•1 bit = 2 colours (black/white)
•8 bits = 256 colours
•24 bits = 16,777,216 colours ("true colour")
•Higher colour depth = more colours available = larger file
The image is stored row by row, pixel by pixel, as a long sequence of binary values. Metadata (width, height, colour depth) is stored in a header at the start of the file.
🎯 Key Points
- •Bitmap = grid of pixels, each storing a colour as binary
- •Resolution = width × height in pixels
- •Colour depth = number of bits per pixel
- •More pixels or more bits per pixel → larger file size
- •Image metadata (dimensions, colour depth) is stored in a file header
0/5 steps completed