Does subtractive colour mixing exist? - PowerPoint PPT Presentation

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Does subtractive colour mixing exist?

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Does subtractive colour mixing exist?

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  1. May 2010 Does subtractive colour mixing exist? Stephen Westland Professor of Colour Science and Technology School of Design University of Leeds

  2. All colour is created by the mixture of three "primary" colours. The three primary colours of paint are red, blue and yellow You cannot mix a primary red, yellow or blue using any other colors. Overview To explain the nature of additive colour mixing To make explicit the relationship between additive and subtractive colour mixing Say some interesting things about colour primaries and colour gamuts

  3. Dogma and Doctrine Empedocles (490-435BC) believed that everything that is permanent is four-fold. The elements fire, water, air and earth were the roots of all things air (sky) water (sea) fire (sun) earth (earth) Greek thought became obsessed with the number four and thus the four-colour doctrine was born: Aristotle – warm, dry, damp cold Hippoocrates – black bile, blood, yellow bile, phlegm Four ‘humors’ – melencholic, sanguine, choleric, phlegmatic Four seasons – winter, sporing, summer autumn Four ages of man – child, youth, man, greybeard

  4. Additive Colour Mixing What is being mixed? Where is the mixing taking place? power power power wavelength wavelength wavelength

  5. Additive Colour Mixing

  6. Univariance 2x M

  7. Rod vision has no colour!!

  8. Trichromacy S M L

  9. The cone response to the mixture of red and green light is the same as for monochromatic yellow However, additive colour-mixing occurs because when an object reflects more than a single wavelength the cone responses are not unique - metamerism occurs. Metamerism Each wavelength produces a unique ratio of LMS responses. Small L and M response Large S response Large L and M response Small S response

  10. Additive Colour Gamut Colour primaries cannot be matched by mixing together other colours!! Colour primaries are (somehow) more pure than other colours!! CIE y CIE x

  11. RGB is not standard CRT LED LED CRT plasma plasma Mobile displays Mobile displays The same RGB values displayed on these devices would most likely result in different colours (unless we have very good colour management!!) The same RGB values displayed on these devices would most likely result in different colours

  12. Subtractive Mixing reflectance The process of mixing would be the same as for additive colour mixing. wavelength However, since the dyes are absorbing, not emitting, the mixtures would be very very dark and dull. reflectance wavelength Besides, dyes that behave like this so not exist!! reflectance wavelength

  13. Subtractive Mixing reflectance Mixing together such broadband red and green dyes (for example) would again result in a very dark colour (black in theory, brown in practice). wavelength reflectance wavelength reflectance wavelength

  14. Subtractive Block Primaries reflectance wavelength reflectance The cyan, yellow and magenta dyes control the red, blue and green light reflected respectively. wavelength reflectance wavelength

  15. reflectance wavelength CMY (Murray 1934) Subtractive Block Primaries reflectance wavelength reflectance Green results from a mixture of yellow and cyan, but the amount of green light present is actually controlled by the amount of magenta dye! wavelength

  16. Broadband absorption spectra In general, the larger (more conjugated) the organic molecule the less energy is required to enable the transition Excited state of dye Absorption of energy Packets of energy are large Packets of energy are small Ground state of dye

  17. Realistic dye reflectance curves Adobe RGB (1998)

  18. Print gamut Additive/Subtractive Gamuts The gamut of a device is the range of colours that it can reproduce Display gamut

  19. Additive vs Subtractive

  20. Vermillion or a lake of cochineal or madder (early C19th) Alizarin crimsom (late C19th) Violet red quinacridone (mid C20th) Cobalt violet? Why RYB?

  21. Why RYB? Thanks to modern intense and lightfast pigments, we can choose much more effective paints than were available to artists of the past, and as a result the traditional primary triad — red, yellow, and blue — is obsolete and should not be taught. Bruce McEvoy – www.handprint.com

  22. Questions? Thanks for listening ;).