Light / Colour

The question of colour and perspective is a complex topic that involves questions of essence, definition and realism. A simple question arises: what is colour and how does it appear and change within perspective views, and why. Finding answers is not so simple.

Colour perspective refers to gradients of changes of hue, saturation, and value and sheen of spectral colours with increasing distance of object/scene from eye. The most common type of colour perspective is a gradient of the sky’s colour from deep azure overhead to light blue or white near the horizon. Also, the browns and dark greens of nearby hillsides go to the azure/blue/green colour for mountains in the distance. These effects are named as atmospheric perspective.

Colour

Visual perception of form is based on light or the electromagnetic spectrum (wavelength property).

Colour is not an inherent property of matter, whereby colour perception is related to an object’s light absorption, reflection, emission spectra, and interference. In humans, colours are perceived in the visible spectrum through three types of cone cells (trichromacy). Other animals may have eyes sensitive to different wavelengths, such as bees, which can distinguish ultraviolet, and thus have a different colour-sensitivity range.

Colours have perceived properties such as hue, colourfulness (saturation), and luminance. Colours can also be additively mixed (commonly used for actual light) or subtractively mixed (commonly used for materials). If the colours are mixed in the right proportions, due to metamerism, they may appear the same as a single-wavelength light. For convenience, colours can be organised in a colour space, which, when abstracted as a mathematical colour model, can assign each region of colour a corresponding set of numbers. Ergo, colour spaces are used for colour reproduction in print, photography, computer monitors, and television. 

Some of the most well-known colour models and colour spaces are RGB, CMYK, HSL/HSV, CIE Lab, and YCbCr/YUV. Because the perception of colour is an important aspect of human life, different colours have been associated with emotions, activity, and nationality. In the visual arts, colour theory is used to plan the use of colour in an aesthetically pleasing, harmonious way. 

Colour Constancy

The ability to see an object’s colour as relatively constant, even when the lighting changes. This is because the visual system adjusts to the light, allowing the object to appear the same colour. 

Explanation 

  • Colour constancy is a type of chromatic adaptation, which is when the sensitivity of the chromatic mechanism(s) change. 
  • The human visual system can’t sense or directly measure the spectral reflectance of objects, which is the proportion of light an object reflects at each wavelength. 
  • The light reaching the eye confounds the illumination and spectral reflectance of the object. 
  • The visual system interprets different colours as the same, even when actually different.

Examples

  • A red apple will look red on a sunny day or cloudy day.
  • A yellow ball will look yellow in sunlight and under fluorescent light. 
  • A coat or car will appear to be the same colour in daylight or under fluorescent lighting.

Eye / Colour

Writing about Leonardo da Vinci’s approach to painting, Kim Veltman said that for Leonardo, as a general category, colour perspective subsumes aerial perspective – and includes Leonardo’s azure law concerning distant objects and perspective of shadows/reflections, all of which Leonardo tested experimentally and included in his artworks to enhance realism. 

Leonardo correctly distinguished different kinds of colour:

  • Original colour of object when illumined with white light: This is the true colour of the object. 
  • Apparent colour of object when illumined with coloured light: This is the apparent colour of the object under specific lighting conditions. 
  • Alterations of colour – due to medium of transmission or psychological effects at detector: Refers to all alterations of colour due to the medium of optical transmission, original colour of the object, and psychological effects in the eye, and/or imaging detector properties.