1. W14D1

2. Multimedia Representation of colour (photos, videos) Representation of sound. Comp.Sci. questions: what is colour? how can computers capture & reproduce colour? Take home message: very difficult to represent colour correctly! physiology and psychology, important! (optical illusions)

3. W14D1 Visible light http://www.yorku.ca/eye/spectru.htm

4. W14D1 Spectral sensitivity of human eye

5. W14D1 Color matching experiments - I Show a split field to subjects; one side shows the light whose color one wants to measure, the other a weighted mixture of primaries (fixed lights). Each light is seen in film color mode.

6. W14D1 Color matching experiments - II Many colors can be represented as a mixture of A, B, C write M=a A + b B + c C where the = sign should be read as “matches” This is additive matching. Gives a color description system - two people who agree on A, B, C need only supply (a, b, c) to describe a color.

7. W14D1 Subtractive matching Some colors can’t be matched like this: instead, must write M+a A = b B+c C This is subtractive matching. Interpret this as (-a, b, c) Problem for building monitors: Choose R, G, B such that positive linear combinations match a large set of colors

8. W14D1 HSV colour model Source: http://www.ncsu.edu/scivis/lessons/colormodels/color_models2.html Primary colours Red Green Blue Secondary Cyan Magenta Yellow Secondary=White-Primary (create colors for print)

9. W14D1 HSV colour model, tertiary colours Add the colours between primary and secondary

10. W14D1 HSV colour model Colour specified by 3 parameters: -hue (angle on disc) - saturation (how dominant is the hue relative to the other colours) -value (overall intensity of the light)

11. W14D1 HSV colour model

12. W14D1 Colour = sensation. It is determined by: -Light -Physiology -Psychology Experiment

13. W14D1 Read the colors of the words in col 1, then col 3, then col 2:

14. W14D1 http://www.michaelbach.de/ot/col_lilacChaser/index.html Experiments with optical illusions: