Colour principles Flashcards
Visible light
Light that we are able to perceptualise
380-760nm
Part of the electromagnetic spectrum
Light consists of wavelengths.
Electromagnetic spectrum
continuum of wavelengths
Short wavelengths make up blue light
Long wavelengths make up red light
Eye structure
Cornea
Pupil
Lens
Retina
Optic nerve - makes up our ‘blind spot”
Accomodation
automatic changing the shape of the lens to focus light.
Retina
Made up of cones and rods, bipolar cells and ganglion cells contains fovea = where visual activity is greatest, has the most cones
connecting cells = amacrine and horizontal cells
Rods and cones
specialized nerve cells that contain light-sensitive chemicals called visual pigments that generate an electrical response to light.
cones= functions in bright light and colour perception. Sensitive to Short Medium and Long wavelengths
rods= functions in dim light
Bipolar and ganglion cells
merge the input arriving from the rods and cones.
Each ganglion cells corresponds to a group of rods or cones = receptive field
Theories of colour perception
Trichromatic and opponent
Trichromatic theory
Presumes that colour perception is a function of the relative stimulation of the three types of cones (blue, green, and
red)
If only one type of cone is stimulated, that colour is perceived
Perception of other colours is a function of the relative ratios of stimulation - yellow light would stimulate green and red cones, and so yellow would be perceived.
Opponent-process theory
colour perception is based on a lightness– darkness channel and two opponent colour channels: red–green and blue–yellow. Presumes colours within each opponent colour channel work in opposition to one another
The actuall way our eyes work.
Simultaneous contrast
Induction refers to when the perceived colour of an area is affected by the colour of the surrounding area, considered to emerge because of the
receptive fields.
Colour vision impairment
(colour blindness)
groups are distinguished based on the number of colours that
must be combined to match any given colour
The most common problem for both groups is distinguishing between red and green
Colour vision impairment types
Anomalous Trichromats (use 3 colour cones) - some difficulty in distinguishing colour
Dichromats (use 2 colour cones) - colours cannot be distinguished.
Hypotheses for colour vision impairment
- a change in the colours to which cone cells are sensitive
- changes in one of the opponent-process channels (normally the red–green)
Subgroups of colour vision impairment
- protanomalous and deuteranomalous for anomalous trichromats
- protanopes and deuteranopes for dichromats
Protanomalous
- can have all three cone types, but their L (long wavelength) cones are less sensitive to red light than they should be
- Red may appear as dark gray, and every colour that contains red
may be less bright
Deuteranomalous
can have all three cone types, but their M (medium wavelength)
cones are less sensitive to green light than they should be
* Mostly see blues, yellows and generally muted colours
Protanopes
are presumed to be missing red - L cones are missing. So, one
cannot perceive red light
* Colours are seen as shades of blue or gold
* May easily confuse different shades of red with black and confuse dark brown with dark shades of other colours, including green, red or orange
Deuteranopes
- are presumed to be missing green - M cones are missing.
- Cannot perceive green light. Mostly see blues and golds.
- May confuse some shades of red with some shades of green and also confuse yellows with bright shades of green
Rainbow colour scheme in cartography
Causes data distortions
Is highly misleading
Transition between colours in not seamless.
Some colours stand out more than others can distort the statistics.
vision impairments or colour blindness may find it impossible or inaccurate to read the data given in a rainbow colour scheme.
Accommodating colour vision impairment in colour shemes
can be accommodated by colour schemes that suit red- or green-blind dichromats and green colour-blindness in mind.
Data graphics can be designed with the most severe kinds of red and green colour-blindness in mind.
Sequential, diverging and qualitative colour schemes have been tried and tested for print and online display and evaluated for legibility by readers with colour-deficient vision.
Sequential colour scheme
Display data with non-midpoint critical values by using sequential colour schemes:
* The most popular colour schemes used in thematic mapping
* Excellent for demonstrating the order of data values
Diverging colour scheme
Uses two complementary colour schemes that diverge from a
common hue to display diverging data
Instead of showing a single progression, however, they visualize the distance of all values from a critical point
work well for depicting data with critical middle value or class
Qualitative colour scheme
Demonstrate differences, but not order, between map classes
* Often used when creating maps of political boundaries, or to create categorical choropleth maps and most common in creating land use or land cover maps
* Used for nominal, but, not ordinal or ratio data
When anomalies are equally
represented the colour scheme is..?
- Perceptually uniform
- Perceptually ordered
- Colour-vision deficiency friendly
- Readable in black & white print
Visual processing system
Information leaving the eyes via the optic nerves crosses over at the optic chiasm; up to that point, information from each eye is separate, but pathways beyond this point contain information from both eyes.
Beyond the optic chiasm, each pathway enters the lateral geniculate nucleus = LGN.
primary visual cortex
Visual information interpretation begins here, the first place where all of the information from both eyes is handled
Interpretation of visual information
Research efforts found three kinds of specialized cells in the primary visual cortex:
* simple cells
* complex cells
* end-stopped cells
fMRI utilizes an MRI scanner, which generates strong magnetic fields
that pass through the human body - may provide insight to the issue of how the brain handles a map.
Changes in metabolic demands of nerve cells are an indication of which area of the brain is activated.
Simple cells
respond best to lines of particular orientation
Complex cells
respond to bars of particular orientation that move in
a particular direction
end-stoped cells
respond to moving lines of a specific length or to
moving corners or angles
