This key facts covers Image Representation - Bitmap Graphics within Images & Sound for GCSE Computer Science. Revise Images & Sound in 3.3 Data Representation for GCSE Computer Science with 18 exam-style questions and 16 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 4 of 12 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Image Representation - Bitmap Graphics
How Bitmap Images Work:
- Pixel: Smallest unit of an image (picture element)
- Grid: Image is a 2D grid of pixels (e.g., 1920×1080 = 2,073,600 pixels)
- Color: Each pixel stores RGB values (Red, Green, Blue)
- Storage: Store every pixel's color = large files!
Key Image Properties:
1. Resolution (Width × Height):
- 1920×1080: Full HD (2.1 megapixels)
- 3840×2160: 4K UHD (8.3 megapixels)
- 4000×3000: 12 megapixels (typical phone camera)
- Higher resolution: More detail but larger file
2. Color Depth (Bits per Pixel):
- 1-bit: Black or white (2 colors)
- 8-bit: 256 colors or grayscale
- 16-bit: 65,536 colors (old games)
- 24-bit (True Color): 16.7 million colors (8 bits per RGB channel)
- 32-bit: 24-bit + 8-bit alpha (transparency)
RGB Color Mixing (24-bit):
Each pixel: Red (8 bits) + Green (8 bits) + Blue (8 bits) = 24 bits total Red (255, 0, 0) = pure red Green (0, 255, 0) = pure green Blue (0, 0, 255) = pure blue Yellow (255, 255, 0) = red + green White (255, 255, 255) = all colors max Black (0, 0, 0) = no color Total possible colors: 256 × 256 × 256 = 16,777,216 colors
Practice questions for Images & Sound
What does colour depth refer to in a digital image?
Explain the effect of increasing colour depth on a digital image. Refer to both file size and image quality in your answer.