Colour Theory and Application

1. Colour Theory and Application B.Sc. (Hons) Multimedia Computing Media Technologies

2. Agenda • Describing Colour • Colour Models and Synthesis • Colour Palettes • Colours for the Web B.Sc. (Hons) Multimedia Computing Media Technologies

3. Describing Colour • Words we might use when naming and describing colours: • ‘shade, hue, warm, tone, bright, dim, pale, intense, vivid, rich, saturated, cold, strong, wishy-washy, glowing, colour, flat, weak, muddy, soft, vibrant, luminance, bold, tint’ • Very subjective - influenced by perception and characteristics of illuminating light source. B.Sc. (Hons) Multimedia Computing Media Technologies

4. Why is colour important?

5. The Visible Spectrum

6. Colour Temperature (deg. C)

7. The Colour Wheel

8. Goethe’s colour wheel

9. Using the Colour Wheel • Colour Wheel video • http://www.youtube.com/watch?v=59QGexKdFUI

10. What about text? • A useful interactive tool: • http://www.hgrebdes.com/colour/spectrum/colourvisibility.html • So, text is different! • You need contrast – but not too much.

11. Colour Models:RGB • Display devices generally use a color model called RGB. • It stands for Red-Green-Blue • Based on the additive synthesis model • RGB colour value specified in three bytes B.Sc. (Hons) Multimedia Computing Media Technologies

12. Colour Models: RGB • Each RGB value is given a number from 0 – 255 starting from Black: R = 0 , B = 0, G = 0 to White: R = 255 B = 255 B = 255 • Thus 256 colours can be represented by one byte = 2 8 • Total possible colours from RGB code is 255 x 255 x 255 = 16 581 375 colours = True colour, but will require 3 bytes per pixel ( 24 bit colour ). B.Sc. (Hons) Multimedia Computing Media Technologies

13. How’s your Hexadecimal? • Base 10 digits= 0 -> 9 • Base 2 digits = 0 -> 1 • Base 16 digits = 0 -> F • Why? • So each byte goes from 00 -> FF • So FF FF FF (R,G,B) = ? • And 00 00 00 =? • 80 80 80 = ? • FF 80 80 = ?

14. Colour Models: Hue, Saturation, Value (HSV) The HSV model is based on the following concepts • Hue - this is what most people would refer to as the colour or shade. Red, yellow, green and blue are hues. • Saturation - this is a value that represents where the colour is on a scale from achromatic white to the pure hue. • Value - is the attribute, sometimes referred to as brightness, which determines how intense the colour is on a a scale from black to the pure hue.

15. HSV 3D Representation

16. HSV 2D Representation

17. The Colour Picker (Maya) B.Sc. (Hons) Multimedia Computing Media Technologies

18. Colour Models: Synthesis • Additive Synthesis - Start with no light. Add red green and blue light to make white and complementary colours • Subtractive Synthesis start with white light. Subtract red green and blue light to achieve complementary colours and black B.Sc. (Hons) Multimedia Computing Media Technologies

19. Additive Synthesis B.Sc. (Hons) Multimedia Computing Media Technologies

20. RGB Additive • Additive color: Combine light sources, starting with darkness (black). • The additive primary colors are red (R), green (G), and blue (B). • Adding R and G light makes yellow (Y). Similarly, G + B = cyan (C) and R + B = magenta (M). • Combining all three additive primaries makes white. B.Sc. (Hons) Multimedia Computing Media Technologies

21. Additive Synthesis B.Sc. (Hons) Multimedia Computing Media Technologies

22. Subtractive Synthesis B.Sc. (Hons) Multimedia Computing Media Technologies

23. CMYK Subtractive • Subtractive color: Illuminate objects that contain dyes or pigments that remove portions of the visible spectrum. • The objects may either transmit light (transparencies) or reflect light (paper, for example). • The subtractive primaries are C, M and Y. • Cyan absorbs red; hence C is sometimes called "minus red" (-R). Similarly, M is -G and Y is -B. B.Sc. (Hons) Multimedia Computing Media Technologies

24. Subtractive Synthesis B.Sc. (Hons) Multimedia Computing Media Technologies

26. Colour Models:CMYK • Cyan-Magenta-Yellow-Key, and pronounced as separate letters. CMYK • Based on the subtractive synthesis model • CMYK is a colour model in which all colours are described as a mixture of these four process colours. • CMYK is the standard colour model used in offset printing for full-colour documents. Because such printing uses inks of these four basic colours, it is often called four-colour printing. • Key is (usually) black – although, in theory, black can be produced with C+M+Y, it looks muddy and most colour printers have a separate black ink cartridge. B.Sc. (Hons) Multimedia Computing Media Technologies

27. Colour Models: RGB & CMYK B.Sc. (Hons) Multimedia Computing Media Technologies

28. Matching RBG to CMYK • One of the most difficult aspects of desktop publishing in colour is colour matching • Properly converting the RGB colours into CMYK colours so that what gets printed looks the same as what appears on the monitor. • RGB Most important for multimedia as it corresponds to the way colour is produced on a computer monitor

29. RBG to CMYK (Photoshop)

30. Palettes (Indexed Colour) • Computer monitors may be able to display 24 bit colour but video driver hardware may be limited to less than 24 bit. • Thus we use a subset of 24 bit in an 8 bit palette – a selection of colours appropriate to the image colours • Palettes provide a finite sub-set of colours required for a given image • If the colour requirements change then some colours in the palette will need to be substituted for others to enable the new colours to be represented • Approximation to original colour in scene B.Sc. (Hons) Multimedia Computing Media Technologies

31. B.Sc. (Hons) Multimedia Computing Media Technologies

32. B.Sc. (Hons) Multimedia Computing Media Technologies

34. B.Sc. (Hons) Multimedia Computing Media Technologies

35. B.Sc. (Hons) Multimedia Computing Media Technologies

38. Web Colours • Websafe colours were specified from the days when most of the web audience could only access 256 colours. • To display intermediate shades, ‘dithering’ was necessary. • Most contemporary display hardware is now able to provide 24 bit colour • Still need to be aware of potential deployment issues for now (e.g. mobile phones) B.Sc. (Hons) Multimedia Computing Media Technologies

39. B.Sc. (Hons) Multimedia Computing Media Technologies

40. Munsell System • Albert Henry Munsell • This system is based on the principle of "perceived equidistance” • Munsell attempts to account for each colour attribute in ordered visual steps. He introduced 100 steps for colour "hue", starting with five main colours and five additional colours, and adopts an ordering system with 10 units of colour "value" and an open scale called "chroma" (similar to saturation) • Used in paint industry and photographic applications

41. Munsell System

42. RGB -> Pantone conversion • http://www.netfront.fr/Services/rgb2pantone/pantone.htm?r=255&g=100&b=100&rgb=

43. References The Colour Group ( founded in 1940 ) 19-11-04 http://www.city.ac.uk/colourgroup/ (City University) Colour Wheel http://www.ficml.org/jemimap/style/color/wheel.htm Visbone Colour Resources 19-11-04 http://html-color-codes.com/l Weinman L. Web Pallets 19-11-04 http://www.lynda.com/ Koren N. Light and Colour http://www.normankoren.com/light_color.html 21-11-04 Roberts M HSV Colour Model. 21-1104 http://www.cs.bham.ac.uk/~mer/colour/hsv.html Munsell System http://www.colorsystem.com/projekte/engl/31mune.htm B.Sc. (Hons) Multimedia Computing Media Technologies