Rainbow - colours in the eye

play with coloursuse of colour 'physics' of colourhow we see colourhow computers do coloursee also www.colormatters.com

play with colourscolour is surprisingly complexphysics, aesthetics, psychologyusing colour can be funexperiment , play with it!context matterswe all see colours differentlyperception of colour depends on surroundingsdifferent at midday or night

the eye of the beholdercontext matters

good use of colourusing conventions (red for alarms etc.)branding parts of an interfaceoccasional emphasisredundant codingi.e. in addition to other meanse.g. web link colours - also underlinedfor diagrams, etc.yucky clip art, but was all I could find

bad use of colourover use - without very good reason (e.g. kids site)colour blindnesspoor use of contrastdo adjust your set!adjust your monitor to greys onlycan you still read your screen?

'physics' of colour colour is the wavelength of lightlike pitch is the wavelength of soundspectrumfrom red - longestto violet - shortestand beyond red infra red (heat) microwaves radioviolet ultraviolet ... nasty radiation7x10-7m4x10-7m

mixing colourmixing paint blue + yellow = green (really cyan)

mixing lights red + green = yellow

called additive and subtractive colour

additive colour - mixing lightphysically both colours in the mixed lightlike a chord in musiclight is really red + greenwe see yellow

subtractive - mixing paintcyan paint absorbs a lot of redyellow paint absorbs a lot of bluecyan + yellow absorbs most of the red and blue leaving mainly green light reflectedso we see green

primary coloursin music we hear chords and harmony C + G Ethere are no primary notes in music

so why three primary colours?

not physics but the eye

in the eyetwo types of sensory cells:rodssee black and white and greybest in low lightgood at seeing movementcones see coloursbest in bright light

how we see colour... three types of cones: red, green and blue!well nearly ... like 3 radios tuned to different stationseach type sensitive to a range of light frequencieseye compares response of each kindeach mix has same response as some pure colour3 receptors => 3 dimensions of colour

rods and coneshow manymore in the centre (fovea) than the edges => better central visionwhere they arecones towards centre, rods towards edge => peripheral vision low-light, good at movement, black and whitehow fastblack and white faster (in brain) than colour

how computers do colour lots of spots of red, blue and greeneye merges them to form colourslike pointillist painting

colours described using RGBamount of each colour they havee.g. #ff00ff = purple

variationsdifferent colour models:HSI, CMYK, CIEused for different purposesscreen depthnumber of bits used per pixel24 = 8 bits per colour (RGB) = 16 million colours32 as above, also alpha channel (transparency)16 = 5 bits per colour = thousands of colours8 too few to split, need designed palettes

palettesmapping:256 colours (8 bits) selection of full (24 bit) RGBoptions:application palettes (why funny things happen!)system palette (slightly different between platforms)web safe colours6 colour levels for each RGB channel 6x6x6 = 216combinations of hex 00,33,66,99,cc,ffe.g. #cc3300, #0000ff, #999999