Monday, 15 November 2010

Colour theory part one

This is a summary of Colour theory based on Fred's seminars and also using the recommended reading book Basics Design 05 'Colour'.  A systematic approach to colour.

'Noun - The sensation produced by rays of light of different wavelengths, a particular variety of this.'

Colour is fundemental to both Graphic design and visual language. When we look at something colour is usually the first thing we register.  Our culture influences how we react to colour and what we associate colour with.  

The Basics


Primary colours

Come in two forms additive and subtractive:
Additive primaries are red, green and blue
Additive secondaries cyan, magenta and yellow
Subtractive primaries are blue, red and yellow
Subtractive ssecondaries are red, green and blue

Tertiary colours

Are produce when a secondary and primary colour combine

Additive Colour

RGB colour is an additive system of colour which we associate with TVs, Computer monitors and scanners. Red, green and blue light projected together yield white.  The additive system without light starts with black.  Varying amounts of red, green and blue light produce different colours.  When the equal amounts of the  primary colours red, green and blue are combined they produce the secondary additives Cyan, yellow and Magenta. 

Subtractive colour

CMYK colour is a subtractive colour system we associate with digital printing,paints and photographs.  If Cyan. Magenta and Yellow mix they produce key (black).  When coloured paints or filters are mixed the resultant colour is caused by subtracting some wavelengths of light and relecting others.  The subtractive systems starts with light and if the light source is anything other than white our eyes can compensate but often give us a 'flawed' perception of the true colour.

Describing colours

Every colour has a unique light wavelength however this imnformation is not useful in differntiating colour.

Hue, saturation and brightness are all used to describe colour in grater detail. 

Hue is what helps us distinguish one colour from another by the unique charcteristics of each colour.

Saturation/Chroma is the purity of a colour.  Depending how near or far from grey a colour is describes the colour's sauration level. When a colour has no grey it is at maximum saturation convesely a colour with increasing grey will be described as lower saturation. 
Bright colours = no grey
Dull colours = more grey 

Value/brightness is how light or dark a colour is.  By mixing white or black with a colour can change its lightness or darkness.  A tint is a colour mied with white.  A shade is a colour mixed with black. 

The colour wheel

The colour wheel illustartes the classification of colour and also explains the relationship between different colours. 

A monochrome is ant single colour on the colour wheel

Complementary colours are opposite each other on the colour wheel.

Triads are any three colours that are equidistant on the colour wheel

How the eye perceives colour 

The eye contains two kinds of receptors: rods and cones. While the rods convey shades of gray, the cones allow the brain to perceive color hues. Of the three types of cones, the first is sensitive to red-orange light, the second to green light and the third to blue-violet light. When a single cone is stimulated, the brain perceives the corresponding color. That is, if our green cones are stimulated, we see "green". Or if our red-orange cones are stimulated, we see "red". If both our green and red-orange cones are simultaneously stimulated, our perception is yellow.The eye cannot differentiate between spectral yellow, and some combination of red and green. The same effect accounts for our perception of cyan, magenta, and the other in-between spectral colors.Because of this physiological response, the eye can be "fooled" into seeing the full range of visible colors through the proportionate adjustment of just three colors: red, green and blue

This subjective individual response to colour explains the need to have a systematic approach espcially in design.  The system most commonly used is Pantone .

A particular system or process has a spectrum of colours called a gamut.

The hexachrome colour system is a six colour separation process which was developed by Pantone.  It adds orange and green to the CMYK process colours. Alone CMYK can only produce 50% of the Pantone PMS colours wwheras Hexachrome can reproduce 90%.

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