Atmospheric Perspective

This section takes a brief look at atmospheric or aerial perspective; which deals with the visual appearance of spatial objects/scenes as affected by the air, light and shade, and colour.

Earth’s atmosphere affects the perception of depth due to light scattering/absorption. Objects closer to the viewer appear more articulate, detailed, and higher in contrast. Objects further back in space are blurrier, lower in contrast and have little detail. Distant objects also tend to appear bluer/greener than close objects. 

The aforementioned ‘atmospheric’ perspective phenomena can operate as depth cues within a live visual perspective view of a physical scene, an artificial drawing/painting, or CGI/VR/XR image of a spatial scene.

Colour Perspective

Aerial perspective is a class of perspective that has been recognised since the time of Leonardo da Vinci; who defined it as natural, artificial, and (possibly in certain circumstances) synthetic perspective. Leonardo also named aerial perspective as the perspective of colour or the way that colours change as the source object recedes from the eye/station point (Leonardo included both diminution of colour and contrast in this process). 

Colour perspective is at once a generic and specific term.

In general terms it refers to:

  • The original colour of an object (white light), or physiological effects in the eye (adaption of perspective variable: window pane, object, and eye).
  • Apparent alterations of object colour (A): due to illumination effects, and/or shading effects in the local environment.
  • Apparent alterations of object colour (B): due to the medium through which light travels.

As a general category colour perspective subsumes:

  • Aerial perspective, including Leonardo’s <Azure> law for distant objects. 
  • Perspective of shadows. 

That distant objects gradually disappear (perspective of disappearance) is an everyday experience that was discussed widely in Antiquity, and results from a reduction in contrast whereby everything becomes gradually darker and less visible (perspective of contrast).

As a specific category, Leonardo’s colour perspective involves experimental demonstrations using the glass pane of linear perspective as well as simple law, whereby it was later qualified (or proven by Leonardo), that dark objects become lighter and light objects become darker with distance. [N.B. Alberti held the opposite view).

Leonardo performed experiments with the diminution of a man (and trees) at distances of 600 feet; whereby he identified 5 stages in the process. In his work, Leonardo refers also to diminution of form perspective, or gradual loss of object outline structure due to contrast blurring as typically seen in both perspective views/images, etc. 

Gradient of Colour Perspective

Colour perspective is a systematic process and can also be named as a gradient of colour perspective; whereby a standard gradient of colour changes occur that are proportional to the amount or depth of atmosphere through which the light travels.

Ergo it is a type of perspective gradient. In particular gradients of colour, acuity, and chiaroscuro (light and shade effects in a drawing or actual image), sometimes collectively referred to as non-linear perspective, are important factors in the illusion and/or impression of depth (within both a natural view and a painting). 

The aerial perspective of painters is the expression of space by graduations of colour, distinctiveness, etc., while linear perspective or simply perspective, is a branch of applied geometry and deals with the apparent directions and dimensions of objects as seen from a certain point in space, called the station point or eye/camera point. 

Gradients of changes of hue, saturation, and value and sheen of spectral colours change with increasing distance of object/scene from eye. The most common type of colour perspective is a gradient in the colour of the sky from deep azure overhead to a light blue or white near the horizon. Also, the browns and dark greens of nearby hillsides go to azure mountains in the distance. 

Deep Space Perspective

Mountain-top perspective or an elevated perspective is an image/view of a spatial scene taken from a high vantage point such as a mountain. Such a view is sometimes named as a ballon, aerial, or spherical/cylindrical perspective, etc. 

A so-called deep-space perspective or far-distance perspective, allows the various processes of atmospheric perspective, or the perspective of colour and contrast to be clearly detected. But it is important to recognise that colour is by no means a simple concept. Distant objects on the whole appear darker than those in nearer zones due to the decrease in observed or detected illumination for objects with increasing distance. 

In sum, far distance perspective, also known as aerial or atmospheric perspective, is the effect of distance on the appearance of objects. It’s a technique used in painting and photography to create the illusion of depth and space. 

Colour Types

We have different kinds of colour perspective.

Object source colour perspective, refers to the actual colour of an object when viewed in white light. Then we have reflected or apparent colour perspective, which refers to the colour of an object when viewed in a specific colour of light.  We also have luminance perspective, which refers to a form of aerial perspective in which distant objects appear darker than nearby objects.

As mentioned, atmospheric or aerial perspective refers to the apparent colour of an object a specific distance from the viewer. And finally, we have psychological colour perspective, which refers to the perceived colour of an object, which may be very different from one or more of the other types of colour due to perceptual processes happening in the human visual system.

Because the perception of colour is an important aspect of human life, different colours have been associated with emotions, activity, and nationality. In visual arts, colour theory is used to plan the use of colours in an aesthetically pleasing and harmonious way. In scientific terms, experts have been able to quantity colour as explained below.

Colour Perspective

  • 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. 
  • Aerial Perspective: Refers to all alterations of colour due to the medium of optical transmission, and original colour of the object (may include psychological perspective).
  • Detected colour: imaging colour detector properties. 
  • Psychological colour perspective: perceived colour.

Visual Acuity

Visual acuity is a term derived from Latin (acutus) meaning acute or sharp; and refers to clarity of vision or ability to distinguish detail (especially at a distance).

Many different factors can affect visual acuity, including focussing visual effects, and detector resolution etc. However, in terms of atmospheric perspective, loss of object outline detail due to contrast blurring, means that the apparent object outline length becomes smaller (outline appears less bumpy) as optical depth increases (contrast blurring). This is blurring of object detail with distance, and is due to atmospheric effects (aerial perspective).

Patently, contrast blurring can become so acute that the details in question disappear entirely, named the perspective of disappearance.

Colour Theory

Visual perception of form/light based on 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. For humans, colours are perceived in the visible light spectrum with three types of cone cells (trichromacy). Other animals may have eyes sensitive to different wavelengths, such as bees that can distinguish ultraviolet, and thus have a different colour sensitivity range. 

Colours have perceived properties such as hue, colorfulness (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, because of metamerism, they may look the same as a single-wavelength light.

For convenience, colours can be organised in a colour space, which when being abstracted as a mathematical colour model can assign each region of colour with 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. 

Photometry

In the 18th century, Lambert first developed the branch of physics known as photometry, whereby he established chiaroscuro modelling which made it possible to calculate and reproduce graduations of light intensity of objects at a distance. He established the scientific law of absorption of light and hence the decrease of light passing through an absorbing medium of uniform transparency, which suggested precise laws for the degradation of colour passing through the air. 

In the 18th century also, other scientists also established laws for the reflection of light from convex and concave surfaces and the refraction of light through media of different densities, developing work first started by Leonardo da Vinci. Ergo non-linear perspective effects which previously were non-mathematical became more mathematical as steady progress towards modern-day CGI, computer ray tracing models, and also Artificial Intelligence perspective images ensued. 

Summary of Atmospheric Effects

Atmospheric or Aerial Perspective effects can be summarised as follows:

  • Gradients of Colour Perspective: 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 in the colour of the sky from deep azure overhead to a light blue or white near the horizon. Also the browns and dark greens of nearby hillsides go to azure mountains in the distance.
  • Diminution of Contrast Perspective: Apparent loss of relative surface brightness: The apparent intensity of light reflected from surface features within a spatial object/scene, due to atmospheric perspective. See aerial/atmospheric perspective. 
  • Diminution of Contrast Perspective:: Apparent loss of object outline structure: The apparent contrast of the outline of an object (visible structure) tends to decrease with distance due to atmospheric perspective. See aerial/atmospheric perspective. 

Perspective Category Theory

Within perspective category theory, in terms of perspective processes, we define atmospheric perspective as a category of natural or environmental perspective or a naturally occurring optical process. In terms of the outcomes of a perspective process (atmospheric light absorption/scattering), we define related perspective phenomena as an optical image form.

A perspective optical image form refers to the overall (possibly transformed) light ray intensity/wavelength detected features or colour/contrast facets of a perspective image/view. 


-- < ACKNOWLEDGMENTS > --

AUTHORS (PAGE / SECTION)

Alan Stuart Radley, March 2020 - 16th May 2025.
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BIBLIOGRAPHY

Radley, A.S. (2023) 'Perspective Category Theory'. Published on the Perspective Research Centre (PRC) website 2020 - 2025.

Radley, A.S. (2025) Perspective Monograph: 'The Art and Science of Optical Perspective', book series in preparation.

Radley, A.S. (2020-2025) 'The Dictionary of Perspective', book in preparation. The dictionary began as a card index system of perspective related definitions in the 1980s; before being transferred to a dBASE-3 database system on an IBM PC (1990s). Later the dictionary was made available on the web on the SUMS system (2002-2020). The current edition of the dictionary is a complete re-write of earlier editions, and is not sourced from the earlier (and now lost) editions.
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Copyright © 2020-25 Alan Stuart Radley.
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