Colour Perception and Optical Effects

Quick overview of colour in design

Design Questions

  • What design elements are perceived first and why?
  • Why are some colours seen more easily than others?
  • Which colour combinations create harmony? Which colour combinations shock?
  • Why do colour illusions occur?
  • How can we use all these factors to enhance communication in designs?

The Eye

As light passes into the eye it comes into contact with the retina. The retina is made up of layers of different cells, including those known as rods (100 million) and cones (6 million)

 

Rod cells are better for low-light vision and enable us to see dimly lit forms but can only sense the intensity of light.

Cone cells can also discern colour, they function best in bright light. Three types of cone cells exist in your eye, with each being more sensitive to either short (S blue-violet), medium (M green), or long (L red) wavelength light. Each type of cell does not just sense one color, but instead has varying degrees of sensitivity across a broad range of wavelengths, but these various wavelengths are classified into the three categories. Human colour perception is most sensitive to light in the yellow-green region of the spectrum. Yellow is the result of the gree-sensitive and red-sensitive cones being activated.

The colour messages from the cones are relayed to the fovea at the centre of the retina.

The Brain

The brain assimilates the red, blue-violet and green impulses and mixes them up, joining information from the two eyes, to interprete the colour.

Most of what we see is based on the memory of a colour.

Some colours register more easily than others: Yellows and greens are perceived before other hues. Red and violet are the most difficult.

Perception Effects

Every colour in 2D space is affected by what us placed next to it. Perceiving optical colours often has to be learned – how to isolate colours from their environment and prevent interference from the brain.

Successive contrast
If one stares at a colour for some time then look away one sees the complement as a coloured glow. If there is no white space then we see a combination of the complement and adjacent colour.

Simultaneous contrast

Colours look very different depending on their surrounding colours.Complementary colours intensify each other and ‘sing’ or vibrate along their edges.

Outlining in white or black can deceive the eye into thinking colours are darker or lighter than they really are, and that there are more or fewer colours. If colours of equal or similar value are juxtaposed their boundary disappears. This can be counteracted by putting high or low value boundaries.

Colours can bloom into new colours depending on what colours are around them.

Transparency effects

Where one colour looks like a ribbon lying over another.

Bezold effect

The entire appearance of a design can be changed just through changing one colour.

Phantom colours

Produced by juxtaposition of hues.
Eg pointillism, divisionism and television screens.

Spatial effects

Hues that are lighter at maximum saturation (yellows, oranges) appear larger than those that are darker at maximum saturation (blues, purples)

When a colour expands in this way it may also seem closer to the viewer – warm colours advance but cool colours recede. But artists can bring any colour forward depending on what other spatial devices they use.

Spatial advancing or receding results from contrasts between colours. Hue and value contrasts are greatest in things close to us and less apparent in things at a distance. Where there is particulate matter forms also appear bluish because of scattering of short blue wavelengths in sunlight.

Colour Combinations: Harmony and Contrast

These optical effects help us to understand our reactions to particular colours and colour combinations.

Colour combinations are conventionally divided into:

Monochromatic : single colour with variations in value and saturation. Break up with patches of neutral colours. Use hard and soft edges making some shapes come forward, others back.

Analogous : low contrast uses several hues lying next to each other in a colour wheel. But what this means depends on which colour wheel is used.

Complementary : high contrast. The opposite colours hold each other in balance and intensify each other. But relative amounts affected by value ie red and green are equal, orange needs more blue, yellow requires even more violet. Mixes of complementaries reduces saturation and contrast.
Double complementary – 2 adjacent hues with their complementaries
Split complementary – colours to either side of complementary

Triadic:
3 colours equidistant. Can be interwoven with more neutral colours.

Tetradic:

4 colours equidistant. Can be interwoven with more neutral colours.

However designing colour combinations is far from a systematic process – there are many different colour wheels and variants of the primary colours. The effects of particular combinations are also highly dependent on prevailing fashions : cultural associations, which combinations the viewers have seen many times before and which seem new etc.

Human perception

Biology of the eye

The human eye senses this spectrum using a combination of rod and cone cells for vision. Rod cells are better for low-light vision, but can only sense the intensity of light, whereas while cone cells can also discern colour, they function best in bright light.

Three types of cone cells exist in your eye, with each being more sensitive to either short (S), medium (M), or long (L) wavelength light. The set of signals possible at all three cone cells describes the range of colours we can see with our eyes. The diagram below illustrates the relative sensitivity of each type of cell for the entire visible spectrum. These curves are often also referred to as the “tristimulus functions.”

Select View: Cone Cells Luminosity



Raw data courtesy of the Colour and Vision Research Laboratories (CVRL), UCL.

Cambridge in Colour:  Colour Perception

Note how each type of cell does not just sense one colour, but instead has varying degrees of sensitivity across a broad range of wavelengths. Move your mouse over “luminosity” to see which colours contribute the most towards our perception of brightness. Also note how human colour perception is most sensitive to light in the yellow-green region of the spectrum; this is utilized by the bayer array in modern digital cameras.

Eye to brain

As light passes into the eye it strikes the retina at the back of the eye which consists of layers of cells including:

  • rods – that perceive black and white and allow us to see dimly lit forms
  • cones – that help us perceive hues. The cones in the eye only recognise red (long wavelengths), blue-viiolet (short wavelengths) and green (middle wavelengths). They relay these colour messages to the cones of the fovea, an area at the centre of the retina, whose cones transmit to the brain.

The brain then assimilates the red, blue-violet and green impulses and mixes them into a single message that informs us of the colour being viewed.

There are many factors affecting our perception of a colour, such as the surroundings of the object, its surface texture, and the lighting conditions under which it is seen. How much of a colour is used, whether it is bright, dull, light or dark, and where it is placed in relation to another colour are also crucial factors in our perception.

– local colour: the wavelengths that are reflected by a surface under consitions of white light
– optical colour: the combination of local colour with light striking it and other surrounding colours

Subtractive processes are more susceptible to changes in ambient light, because this light is what becomes selectively blocked to produce all their colours.

COLOR PROPERTIES: HUE & SATURATION

Color has two unique components that set it apart from achromatic light: hue and saturation. Visually describing a colour based on each of these terms can be highly subjective, however each can be more objectively illustrated by inspecting the light’s colour spectrum.

A color’s saturation is a measure of its purity. A highly saturated color will contain a very narrow set of wavelengths and appear much more pronounced than a similar, but less saturated color. The following example illustrates the spectrum for both a highly saturated and less saturated shade of blue.

Select Saturation Level: Low High
Spectral Curves for Low and High Saturation Color


Dimensions of colour

hue
A colour without any black, gray, white or complementary is called a pure hue and occurs in Newton’s light spectrum. Primary colours are those which cannot be mixed using other colours, secondaries the result of mixing two primaries and tertiary colours, the result of mixing secondaries with one of their adjacent secondaries. Broken hues are the result of mixing these pure hues with their complement to produce browns and greys.

However there is significant variation between colour theorists as to how they identify primary colours, and also between additive methods (RGB used where light is added and where white is the result of mixing all light wavelengths) and subtractive methods (CMYK and pigment mixing as in printmaking or paint where black is the result of mixing all colours).

Moreover pigments are rarely pure. The results from mixing also depend on the relative colour temperature of each of the colours being mixed.

value
Pure hues vary in value from yellow (lightest) to violet (darkest) This means that when mixing them it will also alter the value. If you squint when looking at two hues of similar value they will merge together. When pigments of equal value are mixed together this gives a darker value because more wavelengths are absorbed and fewer reflected.

Value changes convey texture, are used for shadows and form. Sharp contrasts in value produce the effect of precision, firmness, objectivity and alertness. Close values produce feelings of haziness, softness, quiet, rest, brooding etc. Dark compositions give feelings of night, darkness, mystery and fear. Light compositions of illumination, clarity and optimism. Middle values are relaxed and often go unnoticed.
Discords: when the value of a hue is altered by the addition of black, white or another colour opposite to its natural value order eg adding violet and white to make lavender.

intensity (also termed saturation or chroma) defines the degree of purity or brightness (as opposed to light) or how dull (as opposed to dark) a colour is. Pure hues are those where there is no black, white or complementary colour added.
When pure black or pure white are present they are notices before the other hues and colours present.
Pure hues differ in chroma strength – lighter hues have stronger chromatic strength.
Pure hues can be dulled to coloured greys through adding grey of the same value. Or mixing with complementaries to produce a shade.
Neutral greys can be obtained through mxing false pairs – orange and green, green and violet, violet and orange. But they tend to favour one of the parent hues and are less powerful than those made by combining complementary hues. They can also be produced through layering.
Intensity can create effects on objects in space.
– high intensities make an object seem large and pushes it forward in the visual field
– light pure values like yellow advance most on a dark background and least on a white background
– pure hues have a relative strength. if balance is required, they should be used in the right proportion.

temperature
Temperature refers to the warmness or coolness of colour.
– Warm hues are yellow, yellow-orange, orange, orange-red, red and red-violet.
– Cool hues are

Certain colours relax us, others stimulate us.

  • Tone is perceived first, then colours (yellow first), and then the image. This means that the underlying tonal shape structure of an image is of primary importance. Using flat primary colours will detract attention from the image – making colour the subject.
  • Hue is inherently problematic. The effects of mixing different pigment hues will vary depending on issues like transparency, saturation, value. Artists may choose to focus on local or optical colour.
  • Optical mixing occurs as the brain interpretes colours, successive and simultaneous contrast. So perception of hue will depend on the relationship between elements in the composition.
  • Colour responses in terms of perception, meaning and emotional response is a complex combination of hard-wiring of human perception, biological variation (eg colour-blindness) between different viewers and cultural associations.Or use completely arbitrary colours to impose their own feelings and interpretation onto the image.

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