Visual perception, raster displays

CS 248 - Introduction to Computer Graphics
Autumn Quarter, 2005
Marc Levoy
Lecture notes for Thursday September 29
(finished Thursday October 6)

Table of contents:

• Raster displays
  • CRTs: construction, deflection, coating, color
  • Resolution
    • Addressable resolution
    • Physical resolution
  • Refresh
  • Persistence
  • LCD displays
• Spatial resolution - How many pixels do we need?
  • Frequency sensitivity - sine wave gratings
    • Units of measurement
    • Effect of viewing conditions
    • Cutoff
    • Extension to general scenes
  • Phase sensitivity - vernier acuity
    • Receptor spacing and point sampling
    • Vernier acuity and antialiasing
• Temporal resolution - How many frames per second?
  • Flicker sensitivity - refresh rate
  • Motion perception - update rate
  • Motor-visual correlation - lag time
• Intensity quantization - how many bits per pixel?
  • Television chain
  • Graphics chain
  • Quantization for graphics
  • So how many bits?

Note: There is more detail in these notes than I covered in my lecture today, mainly on the topic of CRTs. As I mentioned in class, I am gradually cutting back my coverage of that increasingly obsolete topic. You are not responsible (e.g. on the exams) for material I didn't cover in class. For most classes, the written notes will follow the lectures more closely.

Section D requires an understanding of Fourier analysis, which we won't cover until Oct. 6, but in case you're interested...

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.