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- By shining white light through a prism Newton
demonstrated how it was made up of many colours.
There are two ways of interpreting colour. Additive colours as used by television sets,
subtractive colours by printers.
- Subtractive colours.
- Cyan, magenta, yellow and black (or C M Y K) are
used by printers. Small dots are placed on paper and light falling on the dots is absorbed
the remaining light reflected. This is what the eye sees as colour.
Mixing C M Y can produce black but this is does not usually produce a 'black' black.
- Additive colours.
- A triangular group of phosphor elements made up of the primary colours red, green and
blue (or RGB) are used by television sets, computer monitors, desktop scanners and digital
cameras to display and record almost any colour. All elements turned on produce white
while all elements turned off produce black.
- Different intensities of RGB produce the different colours.
- Colour gamut.
- Is the range of colours that a particular device can reproduce.
- The human eye can see 7 to 8 million colours, and is not consistent across all colours.
- The computer monitor and high-quality colour printer can display at 16 million colours.
The quality of colour can vary significantly between devices.
- The colour chain.
- What colours you see will not be what your scanner sees what your monitor displays and
what your colour printer finally prints.
- Scanning for desktop publishing.
Eye to scanner (RGB), scanner to software (RGB), software to monitor (RGB), software to
printer (CMYK).
- Scanning for commercial printing.
Eye to scanner (RGB), scanner to software (CMYK ), software to monitor (RGB),
software to printer (CMYK). The graphics software must split the output to printer into
four separate files.
- Describing colour using the hue, saturation, brightness ( HSB) model.
- Hue is the actual colour e.g. red.
- Saturation (Chroma, Purity, intensity, vividness).
Measures of the intensity of colour.
- Brightness (value, luminance, darkness)
The amount of light reflected from an object. Maximum brightness is white, minimum
brightness is black.
- Colour perception.
- Perception of colour depends on environment. This includes the type of light around the
subject the type of light falling on it, the light reflected around subject.
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