1. BPC: Art and Computation – Summer 2007 Digital Media - Images Glenn Bresnahan glenn@bu.edu

2. BPC: Art and Computation – Summer 20072 Synopsis Introduction to the physical properties of light and the interaction between light and materials. Describe the biophysics of human vision and the foundations of color perception Describe the representation and storage of digital images Lecture format: http://scv.bu.edu//BPC/MaterialsFall06/lectures/BPC -Class-DigitalImages.ppt

3. BPC: Art and Computation – Summer 20073 Educational Objectives - Light Light as electromagnetic radiation –EMF spectrum –Light as a wave / particle Physical properties of visible light –Frequency, wavelength, speed etc. Absorption, reflection and refraction of light –Color and pigment, reflection and absorption of different wavelengths –Spectral properties of materials

4. BPC: Art and Computation – Summer 20074 Educational Objectives - Vision Basic biophysics of vision Photo-excitation of rods and cones Role of color absorption in cones and perception of color, i.e. RGB color mixing Retinal response, fatigue and flicker fusion –Role in perception of motion

5. BPC: Art and Computation – Summer 20075 Educational Objectives – Digital Images Representation of color as RGB triads Representation of images as a 2D array of pixels Pixels and resolution Storage of digital images –Image file formats –Compression Computer display architecture and display technologies

6. BPC: Art and Computation – Summer 20076 Class Outline What is light? Properties of light How do we see? Digital representation of images Computer display Digital image formats

7. BPC: Art and Computation – Summer 20077 Light and Vision Analogies from sound and hearing

8. BPC: Art and Computation – Summer 20078 Properties of Light EMF spectrum Speed of light Wavelength vs frequency

9. BPC: Art and Computation – Summer 20079 Absorption, Reflection and Refraction

10. BPC: Art and Computation – Summer 200710 Combining Light Frequencies When we combine light of two different frequencies we seem to get light of a different color. Why does this happen? Sound waves don’t combine this way.

11. BPC: Art and Computation – Summer 200711 Human Vision Light passes into the cornea, though a liquid filled chamber and out through the lens. These focus the image The pupil acts as diaphragm, controlling the amount of light The light is projected onto the retina at the back of the eye where a chemical reaction causes neurons to fire

12. BPC: Art and Computation – Summer 200712 Photoreceptor Response Spectrum Cones: S = blue, M = green, L = red Any response can be synthesized by combining red, green and blue light

13. BPC: Art and Computation – Summer 200713 Cell Firings and Flicker Fusion Discrete cell firings, maximum firing rates Flicker fusion frequency –Tricks used in film and video

14. BPC: Art and Computation – Summer 200714 Digital Images Red= 100% Green = 80% Blue = 60%

15. BPC: Art and Computation – Summer 200715 Graphics Display RGB RGB RGB … … … … Frame Buffer Computer Monitor

16. BPC: Art and Computation – Summer 200716 Display Technologies Cathode Ray Tube (CRT) Liquid Crystal Display (LCD) Plasma Display Digital Light Projection (DLP)

17. BPC: Art and Computation – Summer 200717 File Formats Size of digital files Compression –Loseless –Losey Compression and image quality