BPC: Art and Computation – Summer 2007 Digital Media - Images Glenn Bresnahan

BPC: Art and Computation – Summer 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: -Class-DigitalImages.ppt

BPC: Art and Computation – Summer 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

BPC: Art and Computation – Summer 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

BPC: Art and Computation – Summer 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

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

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

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

BPC: Art and Computation – Summer Absorption, Reflection and Refraction

BPC: Art and Computation – Summer 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.

BPC: Art and Computation – Summer 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

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

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

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

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

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

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