Grayscale, gamma, dithering

CS 248 - Introduction to Computer Graphics
Autumn Quarter, 2000
Marc Levoy
Lecture notes for Tuesday, October 10 (second half of class)

Table of contents:

• Gamma correction
  1. Television chain
  2. Graphics chain
  3. Quantization for graphics
  4. So how many bits?
• Color quantization and dithering (covered in more detail than in class)
  1. Quantization without dithering
  2. Quantization with dithering
  3. Adaptive quantization

IV. So how many bits do we need per pixel?

• Synthetic images: 6-8 bits. Some people claim they need more.
  
• Quantization in a linear perceived brightness space: 5 bits looks acceptable (at least for this example)
  
• Scanned/painted images: 5 bits usually ok. Why? Noise breaks up contouring artifacts.
• Antialiased edges: 3 bits suffice! Why? Shorter distance, so contours are compressed.
  This example was also hand drawn, which breaks up contours.