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CM613 Multimedia storage and retrieval Colour

CM613 Multimedia storage and retrieval Colour. D.Miller. What is colour?. Source: http://ccrs.nrcan.gc.ca/resource/tutor/stereo/chap2/chapter2_4_e.php. Perception of colour. Sir Isaac Newton (1643-1727) . Colour Physics.

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CM613 Multimedia storage and retrieval Colour

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  1. CM613 Multimedia storage and retrievalColour D.Miller

  2. What is colour?

  3. Source: http://ccrs.nrcan.gc.ca/resource/tutor/stereo/chap2/chapter2_4_e.php Perception of colour Sir Isaac Newton (1643-1727)

  4. Colour Physics Source: http://www.mic-d.com/curriculum/lightandcolor/electromagnetic.html

  5. Colour Physics

  6. Evolution of the eye (source [3])

  7. Diagram of human eye Containing specialised cells: “rods” – sensitive to light and dark “cones” – sensitive to colour

  8. Rods and cones Source: [2]

  9. Colour (in)constancy

  10. Colour (in)constancy

  11. Colour (In)constancy • Colour perception is influenced by surrounding colours: • http://www.echalk.co.uk/amusements/OpticalIllusions/colourPerception/colourPerception.html

  12. Colour after-image

  13. Colour after-image

  14. http://www.psych.ucalgary.ca/PACE/VA-Lab/colourperceptionweb/theories.htmhttp://www.psych.ucalgary.ca/PACE/VA-Lab/colourperceptionweb/theories.htm

  15. Colour Spaces: Colour Wheel Purest (spectral) colours on perimeter A B Combining pure colours at A and B produces a result along this line

  16. Colour mixing Additive colour mixing Subtractive colour mixing Source 1 http://home.att.net/~B-P.TRUSCIO/COLORSYS.htm http://konicaminolta.com/yourcolours/colour_knowlege_seminar/c_knowlege_seminar001.html

  17. CIE 1931 colour space chromaticity diagram Imaginary GREEN primary Actual perceivable colours X value represents proportion of red, Y represents proportion of green 1-(X+Y) represents proportion of blue http://www.cs.bham.ac.uk/~mer/colour/cie.html http://hyperphysics.phy-astr.gsu.edu/hbase/vision/cie.html Imaginary BLUE primary Imaginary RED primary

  18. Gamut (“range”) http://en.wikipedia.org/wiki/Gamut http://www.luminous-landscape.com/tutorials/prophoto-rgb.shtml http://www.drycreekphoto.com/Learn/color_spaces.htm http://www.naturephotographers.net/articles1203/mh1203-1.html

  19. RGB colour space http://www.cs.bham.ac.uk/~mer/colour/hsv.html

  20. CIE L*A*B* model Commision Internationale de L'Eclairage (CIE) Source 1 Colour solid

  21. Digital data representation of colour Picture element – (pixel, pel) smallest discrete component of an image. Perceived as a coloured dot. more pixels per square cm = “higher” resolution. Bitmap Bitmaps are defined as a regular rectangular mesh of cells called pixels, each pixel containing a colour value. They are characterised by only two parameters, the number of pixels and the information content (colour depth) per pixel 1 bit image (binary image, 1 bit monochrome image) Smallest possible information content for a pixel? Black and white only? Storage requirements? Use for? http://astronomy.swin.edu.au/~pbourke/dataformats/bitmaps/

  22. Digital data representation of colour 8-bit grey-level image how many shades of grey? 8-bit colour image how many different colours? which colours? why lookup tables?

  23. Digital data representation of colour 24-bit colour image how many different colours? storage penalty? 32-bit colour image What is the extra byte used for?

  24. Colour printing http://en.wikipedia.org/wiki/Four-color_printing#Color_separation_process Detail of colour wheel photographic plate in [2]. Scanned at 300 dpi. Scanned at 1200 dpi.

  25. Pixels and halftoning Detail of colour wheel photographic plate in [2]. Scanned at 300 dpi. Scanned at 1200 dpi.

  26. As you might wish it to be Because colour data can be stored and retrieved consistently, colour will be perceived consistently The reality Retrieved colour data is perceived differently when it is presented on different media, and perception is also affected by other factors such as the presence of other colours or the level of ambient lighting.

  27. References [1] Coren, Ward and Enns (1999) Sensation and Perception (5th Ed). Harcourt Brace College Publishers [2] Li and Drew (2004) Fundamentals of Multimedia. Pearson [3] Rosenzweig, Breedlove and Leiman (2002) Biological Psychology. Sinauer.

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