The purpose of this Post is to provide a link to Chapter 10“Illusory pictorial space and light”, from my book, “Painting with Light and Colour”. This provides a simplified explanation of the science behind the ideas developed in earlier chapters concerning ways of creating and/or enhancing effects of illusory pictorial space by means of using mixtures containing small proportions of complementary colours. In the process it explains why the same method can be used to create harmony in paintings. It also explains why colour repetition has the potential, not only to produce visual discord, but also to generate optical excitements.
Members of the University of Stirling Vision Group
In many places in my books, I acknowledge the importance of the role of colleagues from University of Stirling in the development of the new science-based ideas put forward in them. In particular I mention cooperations with scientists from various departments who later were to join me in the University of Stirling Vision Group. The most important of these were:
Alistair Watson (Physics, psychology and computer imagery).
Lindsay Wilson* (at the time working on aspects of visual perception).
Also, although Peter Brophy* did not join our group, he was an ever-available and important source of information on the biochemistry of the brain.
The founding of the Vision Group.
It was in the Autumn of 1984 that Alistair, Leslie and I took the first steps in the setting up of the University of Stirling Vision Group, which was to have many meetings attended by the above named colleagues and other members of the various interested Departments. Its starting point was a package of ideas developed by Alistair and myself, and two core algorithms based on them, produced by Alistair. These were:
A “colour constancy algorithm“, capable of modelling both spatial and temporal colour constancy, which was inspired by our interpretation of how this phenomenon is achieved by human eye/brain systems. As a preliminary step to achieving this main objective, the algorithm has to pick off the information about surface-reflection. Since it was obvious that the reflected-light contained information, we speculated upon how it might be used by the eye/brain. Due to my interest in picture perception, we focused on its potential for computing surface-form, in front/behind relations, and the wavelength composition of ambient illumination.**
A “classification/recognition algorithm”, based on our interpretation of how human eye/brain systems achieves their primary task of enabling recognition.***
We could not help being excited by the early tests of these algorithms and the speculations concerning their potential. In our enthusiasm to push matters further, Alistair suggested we should seek the help of other researchers, particularly ones with expertise in:
Mathematics and computing.
Visual perception with special reference of visual memory.
It was at this juncture that, having decided on a name for what we were hoping would become a collaborative group, we contacted Leslie Smith for his mathematical and computing skills. But this was only a start. Once Leslie was on board, we approached Bill Phillips, whose long standing interest in visual memory had led him to take the plunge into the recently emerging domain of neural networks and learning algorithms. After many Vision Group meetings, much sharing of ideas, many hours spent working on implementations of algorithms, and the writing of a number of working papers, we decided to submit a suite of five grant applications to the Science and Engineering Research Council, who had let it be known that they were looking for groups of researchers working on the use of computers to model the functional principles of neural system. The stated aim of the SERC was to set up a small number of “Centres of Excellence” in this domain. Not only were two of our grant applications accepted (one submitted by Bill Phillips and one submitted by Leslie Smith), but also our university was encouraged to create a brand new Centre for Cognitive and Computational Neuroscience . This empire absorbed the University of Stirling Vision Group which ceased to have an independent existence. Its coming into existence also coincided with my departure from Stirling on my way to founding my Painting School of Montmiral, where I intended to put theory into practice both in my own work and in my teaching. I also had hopes of confirming and, with any luck, extending the theory. Also after leaving Stirling University, Alistair and I were founder members of a small software development company which used ideas developed within the Vision Group as a basis for creating an image manipulation tool. ****
* The links to Bill, Leslie, Lindsay and Peter relate to their current status. Alistair, Karel and Ranald all retired or died before the Internet became the essential information source it has since become.
** My book is full of examples of how fruitful this speculation proved to be.
What we see is not light, but experiences created by neural networks within the eye and the brain (what I often refer to as “eye/brain systems”). Although it is true that the visual world that we know could not happen in the absence of the patterns of light that enter our eyes, it is only made manifest to us as a result of what is going on inside our heads. This Post provides a link to Chapter 9 of my book “Painting with Light and Colour”, which describes two demonstrations that show just how great can be the difference between an image predicted on the basis of readings from a light meter and the one we actually experience.
Edwin Land’s demonstrations
The demonstrations have a personal importance because they played a key role in the story of my quest to explain the paradox inherent in the dogmas of Marian Bohusz-Szyszko(explained in Chapter 2). They were devised by Edwin Land, the famous inventor, as a part of his investigation of the phenomenon of “colour constancy”.
For another relevant source of information on Land’s demonstration please consult “Land’s colour constancy demonstration”, an edited version of a chapter from my book “What Scientists can Learn from Artists”. You might also want to read the original article in “Scientific American, December 1977”. In this Land explained what he described as his “Retinex theory of colour vision”.
Other chapters from “Painting with Light and Colour”:
The main purpose of this Post is to explain what I mean by “Seurat’s new idea”. Most people would probably leap to the conclusion that I am referring to the “Pointillist method” that he developed, and for which he is justly renowned. But the method was never the main idea, which was to “paint with light” (as opposed to merely “painting light”). No previous artist had attempted to do this.
At least since the Italian Renaissance, the artistic community had been particularly interested in depicting effects of natural or artificial light on the appearance of objects and scenes. They made impressive progress by conceiving matters in terms of whole-field lightness relations (chiaroscuro). Seurat’s new idea opened up the unexplored possibility of introducing the dimension of colour into the mix. In doing so, whether directly or indirectly, he was responsible for opening the way for the possibility of adding a new dimension to the experience provided by representations of the effects of light in paintings.
In itself, this step could justifiably be described as a “quantum leap”, but as it turned out the influence of Seurat’s new idea was to have other far reaching implications. In time it would also lay the foundations for enhancing, not only effects of “illusory pictorial space” but also the sense of both “surface” and “surfacelessness” in paintings.
But even this was not all, for another side-effect of Seurat’s new idea was its contribution to the explosion of colourfulness in paintings. This had been kick started by the discovery by scientists that colour is not a property of surfaces in the external world, but a creation of eye/brain systems. In the wake of this mind blowing reality, earlier Modernist artists were already using brighter colours and juxtaposing complementary pairs, but two requirements of the Pointillist method pushed matters significantly further. These were:
The systematic use of juxtaposed complementary colour pairs, within the optically mixed arrays of tiny dots that characterise Pointillism.
The need to conceive of colour mixing in terms of a colour circle with many more segments than the six segment one (consisting of three primaries and their three complementaries) favoured by the Impressionists. Seurat’s idea meant that he had to represent as many parts of the visible spectrum as possible. To do this he needed to make use of the widest range of the most fully saturated pigment colours available.
Between them these innovations had the effect of hugely increasing the range and subtlety of both colours and colour combinations to be found in paintings produced after 1886, the year that Seurat first exhibited “La Grande Jatte”, his game-changing painting.
For more details click on the link below to Chapter 8 of my book “Painting with Light and Colour”. For those who have not read the previous four chapters, the next section provides a short resume of them (links to the chapters themselves can be found at the bottom of this page).
Short resume of previous chapters
Chapter 4: Describes the Renaissance approach to painting light, which centred on local and whole-field lightness relations with particular reference to finding the darkest and lightest regions in the scene (chiaroscuro) and gradations of lightness across surfaces. In this scheme of things the depiction of shadows was a matter of painting “what you see”, which seemed reasonable enough, but brought with it all sorts of unsuspected problems.
Chapter 5: Focuses on the scientific revolution in the understanding of light and colour that had its origins in the work of Isaac Newton and the insights of the numerous scientists who realised that all sensory experiences including those that relate to colour and effects of light are made in the head. Newton clarified the physical nature of light. The perceptual scientists introduced concepts like the“three primaries”, “induced colour”, “complementary colours” and “colour/lightness contrast effects”.
Chapter 6 : Shows that the Impressionists had an agenda which included the idea of emphasising the reality of the picture surface and playing off the ephemeral and the permanent aspects of appearance.
Chapter 7: Uses photographs to elucidate the meaning of the words “opaque”, “translucent”, “glossy” and “matt”. Particular attention is given to effects on appearances of interreflections and viewing angles.
The diagrammatic origin of Seurat’s new idea
As it does not appear in Chapter 8, but earlier in the book, I am including in this Post the diagram from a physics book that kick started Seurat’s new idea. It was from this that he learnt that the white daylight light that strikes a surface interacts with it in one of two ways:
One part enters the surface and is scattered around inside, before being scattered back out again. While inside, some wavelengths are absorbed. The remainder are scattered-back-out again to produce the limited wavelength combinations that give us “body colour”.
The remainder never enters the surface, but is reflected back directly from it (as from a mirror), such that it leaves it without changing its wavelength composition to produce “reflected light”.
The component that interested Seurat is the “reflected light”. By combining his understanding of this with the discoveries of perceptual scientists mentioned above, Seurat believed that he could represent it in paintings by means of mosaics of tiny dots containing juxtapositions of complementary, or near-complementary, pairs.
When new students at The Painting School of Montmiral are first faced with a live model in a figure drawing class, the majority of them give little time for preparation, even for long poses. Within a matter of seconds, even experienced artists have embarked upon active mark-making. It does not seem to occur to them that, before drawing the first line, it might be useful to spend time familiarizing themselves with the situation that faces them. If this is the case, they will almost certainly be denying themselves an important opportunity.
The feeling-based drawing lesson
At the heart of my book, “Drawing on Both Sides of the Brain“, is a feeling-based drawing lesson that is described in three chapters. Chapter 9(link below) is about getting ready for drawing the first line. Chapter 10 (to follow) gives a blow by blow account of the main lesson in which:
Precise instructions are given concerning the preparation and execution of every line and every relationship.
Detailed reasons are offered for each and every one of these instructions. These relate to scientific studies of how artists coordinate their visual-analytic and line-output skills when drawing from observation.
Chapter 11 (to follow) suggests follow up exercises.
Preparation in previous chapters
All the chapters preceding Chapter 9 have been preparing for this lesson. Thus, they have discussed:
The pros and cons of widely used teaching methods.
The importance of scientific findings in the development of artists ideas.
How more recent scientific findings relating to the eye/brain’s analytic-looking and motor-control systems can help with issues of accuracy, line production speed, self-confidence and self expression.
Preparation in Chapter 9
Chapter 9 is likewise getting things ready for the drawing lesson, but in a much more specific sense, starting with practical issues such as setting up the easel/drawing board, establishing a viewpoint, deciding whether to shut an eye, etc. But it also introduces a certain amount of science-based information that will be useful in explaining reasons for the instructions used in the drawing lesson.
As Chapter 9 contains footnotes that refer to diagrams with explanations to be found in the Glossary, I have included three of these:
Figure 1 is the flow diagram representing the main factors that contribute to the analytic-looking cycle.
Figure 2 indicates regions of the neocortex (new brain) involved.
Figure 3 provides a mapping of eye movements showing glides and saccades.
The boxes and arrows in Figure 1 can be related to regions in the neocortex illustrated in Figure 2. Notice that Visual Area 1, which takes input from the retina via the optic nerve, supplies information not only for the preconscious processes that enable recognition, but also for the subsequent consciousness-related ones that accompany analytic-looking (This is why it is labelled “twice used information resource”).
In addition, the diagram indicates the key role of memory stores (whether short-term or long-term) in enabling both recognition and learnt-actions. It also calls attention to the importance of context and feeling in building them up and ofwhole-life experience in determining how they do so. But perhaps the most important lesson that can be drawn from it is that recognition takes place before analysis. Thus it can be asserted that, in an important sense, “we know what we are looking at before we are consciously aware of it”.
Recognition also takes place before the implementation of learnt-actions, such as those that guide artists when drawing contours or making any other kind of mark. Accordingly, we can draw “what we know” about an object-type on the basis of the multi-modal, preconsciously acquired information made available by the very limited number of looks that are required to enable recognition (seldom more than one or two). In other words, the eye/brain acts as if further analysis of the object itself is unnecessary. The diagram also indicates the role of non visual-inputs in enabling recognition. For example, we may recognise something, in whole or in part, by its sound, smell or feel and can in princple complete the process of doing so without confirming what it is visually.
Figure 2 maps a number of the functional divisions in the neocortex (new brain). These can be related to the stages of the analytic-looking cycle as diagrammed in Figure 1. Thus:
The arrow labelled “visual cortex” points to the location of “visual area 1” in Figure 1
The region from there down to “temporal lobe” corresponds to the labels “preconscious multimodal processing” and “recognition” in Figure 1.
The motor cortex mediates “learnt actions” in Figure 1.
The parietal lobe underpins “conscious analytic-looking” and “the constancies of shape, size, and orientation” in Figure 1.
However, the area in Figure 1 labelled “context” and “feeling-based memory reflecting whole life experience” is more difficult to place, but would include:
Parts of the “frontal lobe” with its links to the emotional centres in the old brain. These are thought to be involved in the choice between “good” and “bad” actions and the determination of “similarities” and “differences” between things or events, both of which are essential to developing the skills that underpin drawing from observation (as explained in Chapters 9 – 11).
The frontal lobe, along with old brain regions including the hippocampus, is also thought to play an important part in the creation and retention of long-term memory.
Figure 3 is based on a photographic record of typical eye movements in which slow moving glides (wobbly blue lines) are interspersed with faster moving saccades (straight red lines with arrows to represent speed). The glides provide a constant stream of same/different information, while the saccades enable an intermittent averaging of input that is useful for neural computations that require knowledge of ambient illumination. The average glide/saccades combination lasts approximately one third of a second.
Other Posts that publish chapters from “Drawing on Both Sides of the Brain”
The word “abstract” is commonly used to refer to a wide variety of paintings. Therefore, there is clearly some confusion as to precisely what it means. This is partly because its usage by artists and critics has evolved over the years and partly because its subtleties have been degraded by an uninformed public. One unresolved issue is where to draw the line between “figurative” and “non-figurative”. Few nowadays would describe Paul Cézanne as an abstract artist (see image below), yet his working philosophy exemplifies the original meaning given to the word.
This Post, like many others, is an illustrated excerpt from “Having fun with creativity”, Chapter 10 of “Fresh Perspectives on Creativity”. What is meant by “having fun”, is enjoying a process by which thoughts, however trivial or wrongheaded, lead to a mushrooming of other thoughts and, thereby, to an exploration of issues that otherwise might be passed over. What follows, not only touches on the subjects of abstraction and construction in painting, but also how these relate to the processes by which the eye/brain systems synthesise meaning from visual input. The four sections are headed: 1–ABSTRACTION, 2-CONSTRUCTION, 3-CHANGES IN MEANING and 4-IMAGES OF PAINTINGS (illustrating, “Abstracting the essence” and “Constructing from the basic building blocks of visual perception”).
What is an abstract painting?
So what qualifies as being an abstract painting? An explanation as to why the word “abstract” was chosen in preference to other words offers a start to the answer. Why not “extract” or “subtract”? It is worth asking such questions because doing so can help a process of refining understanding. It enables the use of same/difference judgments within the domain of words as a means of creating and/or nuancing our sense of their meaning. Thus:
The word “extract” means take something out of something.
The word “subtract” means take something away from something.
In either case the original something is diminished. In contrast:
The word “abstract” means distilling the essence of something, with the implication that this can be done without loosing essential meaning.
Accordingly, the word “abstract” seems best of the three because it implies the possibility of finding what is valuable with the least collateral damage. This is why it was chosen.
However, there is still much ambiguity that requires clarification. If we take the example of the “abstract” of a scientific paper, it is easy to see that however well written, something must have been lost, since otherwise there would be no need for the paper itself. In the case of artists’ abstractions from natural scenes, the situation is less clear, particularly since the image of every scene that comes to our consciousness is produced in the first place through the mediation of eye/brain processing systems that arrive at their conclusions by means of a complex blend of selective and constructive processes. We look at a coffee mug differently according to whether our intention is to drink from it or to make a drawing of its outline. When we want to drink from it, we will normally bypass all information about it except that which is necessary for picking it up and putting its brim to our our mouth. When we draw its outline, we need to make judgements of relativities of position, length, orientation, curvature, etc., and we can safely ignore the information needed to drink from it.
Nor, in this context, should we ever forget that what we experience as “seeing” depends heavily on information coming from non-visual sources accessed (a) by other sensory systems and (b) by memory-stores that have been built up and refined during a lifetime. Thus, both the knowledge that it is coffee time and the smell of coffee, provide context that helps our visual systems to home in on the coffee mug. When we are confronted by a landscape, the way we look at it and the information we derive from it are determined by a mixture of current contingencies and our life’s experience. No two people would find the same essence in it. Indeed, it is now clear that in creating conscious visual experience, our eye/brain systems ignore a great deal more of the information coming into our eyes than they make use of. A mathematician might suggest that they ignore an infinite amount of it.
So how do these facts help us to think about looking at paintings? What differences are there between looking at a real world object and an image of it found in a painting? Generally speaking, when we look at a painted image, situated in illusory pictorial space, the information available will be much less than can be accessed from the real world object. For example, no matter how photographically realistic it may be, an image painting onto a flat surface will not provide the eye/brain systems with the kind of spatial-depth information that is created by means of either stereopsis or motion parallax. Likewise, a sketchily produced portrait will contain much less information than an actual face.
But what is the effect of this impoverishment of available sources of information on the efficiency of the eye/brain visual systems? Does it make their task more difficult? Not necessarily so. As indicated above, all correct classifications are achieved without taking a great deal of potentially relevant information into account. It is worth remembering that efficiency can be defined as achieving an objective with the least possible effort. In the case of the impressive efficiency of eye/brain systems, this means overlooking as much visually available information as is feasible. If we take full advantage of contextual information coming both from other sensory systems and from memory, it can mean overlooking practically all of it. Elsewhere, I give the example of a blur of redness being a sufficient cue to identify a familiar dress in a familiar wardrobe in which it is known that no other red dresses have been placed.
This impressive degree of parsimony has interesting implications for artists. For example, does it mean that a blur of red could adequately represent the dress in a painting? The answer to this question depends on what is meant by the phrase “adequately represent”. In the obvious sense, the answer must be “no”. Nobody would expect the woman in question to reach out for the painted image of a red dress in the wardrobe in the expectation of being able to wear it. On the other hand, the red in the painting might trigger either “feelings” or “memories” associated with the history of the dress that the real dress would not. If it does, how could this influence the experience of people looking at paintings? Two questions, bring us nearer to an answer:
Could feelings be stimulated by a particular red as itself. For example, it is perfectly possible for the colour of an individual stick of chalk pastel to access deeply embedded associations that trigger powerful emotions. If so, could these be added to the experience generated by a pastel painting of the red dress? Of course they could: I thought of the example because I know of an artist for whom love of her pastel sticks was integral to her way of making paintings.
If the the act of seeing the patch of red paint triggers “memories”, how much information could be added from memory stores? And, would these additions be more or less authentic than the information that would be accessed by the woman, if confronted by the actual dress? Since, the real object presents a maximum of information about its characteristic, there is no doubt about the theoretical answer to this question: the real dress has every advantage. But the question for the artist is not whether the red dress would provide more information, but how much of it would be used in practice and for what purposes?
Remember that efficiency can be defined as getting the best results by means of the least amount of effort. In the case of locating the real dress in the real wardrobe, this means identifying it with the least amount of looking. As explained above, the eye/brain systems regularly achieve wonders of parsimonious looking by making maximum use of “context” and “memory stores”. It follows that, the very familiarity of both the dress and its location would make it possible to achieve the goal of finding the dress while overlooking the totality of information other than the blur of redness.
However, the question arises as to whether this massive overlooking mean that the pictured dress might have the advantage over the real one when it comes, either to the amount of information about the dress actually acquired or to the potential for providing stimuli for the creative imagination? In both cases, the answer must be in the affirmative, since it could be argued that a pictured dress:
Would provoke the eye/brain systems into extra analysis, on account of its being less familiar than actual dress.
Would leave extra room for flights of the imagination, on account of its lack of interpretation-constraining details.
In other words, there are good reasons for concluding that, in practice, if not in necessarily in theory, an image of a depicted object perceived as being in illusory pictorial space will regularly, if not always:
Provide the eye/brain with more information than the real world object it represents.
Act as a better catalyst for the creativity of the imagination.
Needless to say, this is one of the many advantages that paintings have over nature.
The influence of others
Another possibility is that the dress-owning woman may fail to make a connection between the patch of red in the painting and the dress it was intended to represent, but that a friend does make a connection. If the friend shares her experience with the woman, by doing so she will be adding another level of context and, thereby, in all probability, causing a change in the meaning of the patch of colour for the dress-owning woman. Significantly, the revised significance could be achieved without making any changes to the actual colour.
But this is not all. One thing of which we can be quite certain of is that the representation of the dress in the head of the friend will be very different to that in the head of its owner. There is no possibility that both will have the same associations between the dress and happenings in their very different life stories. The interesting implication for artists is that what applies in the case of the two friends, also applies to them. When they apply a colour to a painting, they can have no way of knowing all the associations it might trigger in any one other person. Speaking generally, all human beings can say or do things that act as catalysts to the experience of others that are inaccessible to themselves. Indeed, it is difficult to see how communication between individuals could take any other but in this essentially catalytic and creative form.
But all this talk about “abstraction” in paintings and by the eye/brain systems has a soft underbelly for, as we all know, for some time now, the word “abstract” has been routinely applied to paintings that have absolutely no reference to nature, let alone to some essence extracted from it.
In the early 20th century, a number of painters and sculptors acknowledged the significance of this flight from representation by calling themselves “Constructivists” . These pioneers of non-figurative art adopted a radically new approach to their work that had much in common with the physicists of the day, who were on the trail of the building blocks of matter and the principles by which they are combined. Thus, the artists sought to identify the “primitives” of visual perception and to find objective principles for assembling them into art works.
By the fact of approaching paintings in this way, these artists saw themselves as challenging the long held assumption that painting should start from nature. Accordingly, it would be inappropriate to describe their work as distillations of it essence. For a growing number of them, including Kupka, Malevitch, Kandinsky and Mondrian, an alternative was needed that would be founded on a combination of the most basic elements they could think of and simple principles of construction. Over the years, this change of emphasis was reflected in the emergence of a host of different words or phrases to describe how different artists approached building on these foundations – “Constructivist”, “Non-objective”, “Concrete”, “Op”, “Systems”, etc., but all could be places under the umbrella of “Constructivism”.
3-CHANGES IN MEANING
As time passed the situation became more and more complicated. On the one hand there were critics trying to provide more precise classification and on the other there were artists exploring an ever expanding range of possibilities. Distinctions got blurred and terms like “Abstract Expressionism” confused the issue. The artists who were known by this name, were no longer abstracting from nature but rather attempting to make manifest their innermost feelings or allow universal forces to become manifest through them. In this situation, while artists were likely to choose and cling to one or other of the cavalcade of different meanings, the generality of people adopted the catch-all, common usage of today. For them the word “abstract” means anything that is not too closely tied to representation.
Students sometimes ask me to explain “abstract art” to them. As this request is almost invariably made by people whose focus has been on representation, I tend to answer in terms of the origins of the word. I point out that artists living in the second half of the 19th century, influenced by recent developments in the science of visual perception, became aware that all paintings could be described as an “assemblage of regions of colour on a picture surface”,*as interpreted by eye/brain processing systems. Once this conceptual step had been taken, it was only to be expected that, for some artists at least, the idea of looking to nature as the fount of all inspiration was bound to be questioned. From then on, it was only a matter of time before many artists either loosened their ties with representation or completely cut themselves off from it.
As for deciding which word we should choose when talking about any particular painting or group of paintings, including ones we have painted ourselves, my answer would be to take your choice in the light of the considerations discussed above. Perhaps, the main objective should be that you yourself understand the issues, at least well enough to be able to explain them to anyone who asks questions about your work. Meanwhile, the general public will continue to think of “abstract” as more or less anything non-figurative and pretty well everyone will have personal opinions about what counts as figurative. The difficulty lies in deciding on which point on the figurative/non-figurative continuum.
Abstracting the essence
Constructing from the basic building blocks of visual perception
* Quotation from the Nabis artist Maurice Denis.
** Quotation from Bonnard.
Other posts from “Having Fun with Creativity”, Chapter 10of“Fresh Perspectives on Creativity”
Experience with new students suggest that there is a need for clarifications on the meanings of the word “colour” and related words and phrases. I believe that this is because how-to-do-it books on the uses of colour in paintings too often rely on once widely believed scientific explanations that are now outdated, misleading or just plain wrong. The following excerpt from the Glossary to my books on drawing and painting provide answers to the questions listed below, and many others.
What is meant by “body colour”?
What is the difference between “brightness “ and “lightness”?
What is meant by “reflected light”?
How can colour be used to enhance perceptions of illusory pictorial space?
Are “black” and “white” colours?
Are cast shadows black?
What follows relates to several already published Posts. For example:
In everyday language the word “colour” has four main meanings. The first three of these can be explained in terms of the interaction between surfaces and the light that strikes them as diagrammed in Figure 1.
“Surface-reflection” : A part of the incident light is reflected directly back from the surface without changing its wavelength combinations. This is“surface-reflection” and is one of several sources of information that enables the eye/brain to create the experiences of surface-solidity, surface-form and in front/behind relationships.
“Body-colour”: The remainder of the incident light enters surfaces and interacts with the pigments in them, such that some of its wavelengths are absorbed (i.e; turned in to non-visible electromagnetic energy) and the remainder is scattered about within the surface, before being scattered back out again into the eyes of the viewer. It is this scattered back out light that gives surfaces their “body-colour”, enabling us to see the surfaces as their characteristic colour (e.g. red, blue, brown, grey, skin colour, leaf colour, earth colour, sky colour, etc.).
“Transmitted light”: In some cases, a surface can be viewed from the side opposite to the light source, in which case, it is said to be “translucent”. When this is the case, the light that enters a surface and interacts with the pigments in it is scattered out on the other side, into they eyes of a viewer. Accordingly it is described as “transmitted light”. It is this that that gives us the colours of stain-glass windows and translucent leaves when seen against sunlight. In the virtual absence of surface-indicating reflected-light, we perceive such colours as both surfaceless and formless. Two other examples of familiar, perceptually surfaceless colours are the blue of the sky and the colours of the rainbow.
The fourth meaning is more prosaic:
Paint or pigment colour: The word “colour” is also used to describe any selection from the gamut of paints, pastels or crayons used by artists to give colour to their paintings. Thus we talk about the “colours” contained in our paint box, or of the “lemon yellow” and “cobalt blue” tubes of paint to be found in it.
Colour 2: Colour, light and physics
While in everyday language “colours” are referred to with words like “red”, “blue”, “yellow”, “pink”, “brown”, “grey”, etc., and we are all familiar with what they mean, physicists have preferred to describe them in terms of electromagnetic energy and combinations wavelengths and levels of intensity. Accordingly, they are likely to describe the three cone-receptor types in the retina at the back of the eyes as being relatively sensitive to “short”, “medium” and “long” wavelengths. However, even physicists can lapse into referring to them, more colloquially, as “blue”, “green” and “red”, a slippage which can lead to significant misunderstanding. If we wish to understand the nature of colour vision, it is important to realise that knowing the wavelength of the light coming into the eyes from a surface is by no means the same as knowing its colour. Light has no colour: Colour is a creation of eye/brain systems gathering and comparing information from arrays of inputs (as explained elsewhere in these Posts, as well as in the chapters of my books).
One consequence of this fundamental truth is that, although there is indeed a correspondence between wavelength profiles and the colour perceptions that they stimulate, this is not as simple as many people to believe. It is only occurs if all the wavelength profiles entering the eyes from all parts of the scene being analysed during the colour-creating process are taken into account. Likewise, our experience of colour in paintings does not depend simply on the absorption/reflection properties of individual regions of pigment colour but rather on the absorption/reflection properties of all the regions of pigment colour on the entire picture surface. In other words, they depend on “whole-field colour relations”.
As with all words with a long history, the word “colour” has evolved in terms of its meanings and it is therefore it is important to be careful when using it. Most commonly it is used to describe visual sensations that are experienced as attributes of surfaces or regions of surfaces in the external word. We talk of “red” roses or “green” grass because we have learnt to use these words to describe our experience of “red” and “green” objects that we come across in daily life. However, in the eighteenth century, scientists of visual perception realised that colour is not anything of the kind. Rather it is a creation of eye/brain systems based not only on information coming into the eyes from the surface that is being perceived as coloured, but also from the surfaces that surround it. In short, they realised that the experience of colour is both brain-made and context sensitive. Together these two insights made it clear that the colour of a surface cannot be equated with wavelength combinations of the light reflecting from it, as physicists had been doing. For more on this see the section on colour constancy under the constancies in this Glossary.
Soon after the physicists made new contributions to the progress of understanding about colour by going deeper into the subject of the information that the eye/brain picks up from surfaces. What they found was that it is made up of two components with very different properties. In this series of books these are called “body-colour” and “surface-reflection”. Figure 1 shows that when daylight, containing all the visible wavelengths strikes a surface it is divided into two parts:
One part penetrates the surface. When inside, some of its wavelengths are absorbed and others, having been scattered around inside, are scattered back out again into the eye of an observer. This is the “body colour” (what we see as the green of leaves, the yellow of ripe corn, the flesh colour of flesh, etc.). As far as I know, nobody has estimated the number of different body colours in the visible world, but there are clearly at least many thousands.
Another part never enters the surface. Rather it is reflected directly off it according to the rule the angle of incidence is equal to the angle of reflection. Since no light is absorbed during this process, the incident light and the reflected-light contain the same wavelength combination. In the diagram both are shown as being the same “white” light.
In the interests of simplifying its message, Figure 1 only shows one ray of incident light. In the real world light arrives at surfaces from a combination of primary light sources (coming from one or more different directions) and a multiplicity of secondary light sources of different of intensities (coming from a multiplicity of different directions). While primary light sources can have fairly predicable wavelength/intensity profiles, secondary light sources never do: The likelihood of any two combinations of them being the same is negligible. The resulting complexity is such that no part of any one surface reflects the same wavelength/intensity combination as any other part of it. Likewise, no two surfaces in any scene reflects the same wavelength/intensity combination. Physicists would describe the consequent variety of in the composition of the reflected-light that results as infinite. However, for the perceptual scientist, the limitations on the sensitivity of their visual systems restrict the number of nuances of which human eyes can be aware. How many is disputed, but it is generally agreed to be in the millions.
Colour 4 : black and white are colours
In the 1980s Semir Zeki, when investigating area V4 of the visual cortex, found twenty-two “colour coded cells”. These respond to body-colour independently of their wavelength profiles. The twenty-two not only included “violet”, a colour that has no simple wavelength equivalent, but also “black” and “white”. This means that the eye/brain responds to achromatic regions of surfaces in precisely the same way as it responds to regions of blue, green yellow, orange and red. This definitively resolved the question as to whether black and white are colours, although the fact that they are indeed so was already a widely accepted implication of the discovery well over 150 years earlier that colours are made in the head.
Colour 5: Shadows
More recently, the discoveries of the physicists have been combined with the ideas of the perceptual scientists to explain how the eye/brain is able to separate surface-reflection from body-colour. Details of how this is done are given in “What Scientists can Learn from Artists”, Chapters 13 and 14. However one part of the computation depends on the sudden changes in the profile of the reflected-light that regularly occur at the edges of regions of colour (whether at edges of regions of different pigmentation within the same surface or at edges of the surfaces themselves) being equated with changes in body-colour. However it turns out that the computations concerned cannot distinguish sudden changes in actual body-colour from those that occur at the edges of cast shadows (due to sudden changes in intensity relative to adjacent illuminated regions of surface). Accordingly our eye-brain systems classify these erroneously as “body-colour”. Accordingly, as far as the eye/brain is concerned the colour of shadow is just as much a colour in its own right as the blue of the sky, the red of a tomato, the yellow of a lemon, the green of a leaf, the white of snow or the black of soot.
Michael Kidner , the artist, was a teacher at the Bath Academy of Art, when I was a student there. In my view, he was one of the most interesting and important artists of the late 20th and early 21st centuries. It was my great luck that I was able to form a friendship with him that lasted over forty years, until his death in 2009. In 2007 he had a one man show at the Flowers East Gallery, London, to which he gave the title “No goals in a quicksand”. I was asked to help with the writing of the catalogue.* One of my contributions was a slightly edited version of a chapter from “Fresh Perspectives on Creativity”, a book I was working on at the time and which is now one of the four books I am currently publishing in installments on the Posts Page of this website. My other main contribution to the catalogue was an introductory piece called “Michael Kidner the man”, which you will find repeated, after Figure 1 below. To complete this Post, I have also included a link to the chapter on Michael (“The big bang, chaos and the butterfly”) and an image of Michael’s last finished painting (Figure 2):
Michael Kidner the man
When considering Michael’s work, it is easy to concentrate attention too much on the science-based ideas and too little on the man and his feelings. As I have got to know him well, I have been impressed by a quality which I am tempted to call ‘naivete’, since it reminds me of a quotation from Matisse: “The effort to see without distortion takes something like courage and this courage is essential to the artist, who has to look at everything as though he saw it for the first time.” Michael looks at mathematically-based systems in this spirit and is not daunted by his shortcomings as a mathematician, of which he is only too aware. Thus, though characterising himself as groping towards an understanding of matters beyond his realistic grasp, Michael does not see this as a reason for abandoning his obsession with mathematical propositions. He sees these as relating to the fundamental mysteries of science and he looks at the evolution of systems, generated by a simple logic, in much the same way as Cézanne must have looked at natural objects, with total concentration and never ending wonder at the seemingly endless layers of novelty that open up before him. In other words, though he works with the ideas of science, he responds to them with the sensibility of an artist, experiencing them with innocent and ever inquisitive eyes. It is his personal and, therefore, quintessentially different visual response that reveals and creates, not only the perceptual excitements but also the metaphors for the human condition that are to be found in his work. Michael works slowly and doggedly. Daily he clambers up to his attic studio where he spends untold hours, apparently oblivious of time and human needs, patiently searching for the key that will give meaning to his latest quest. His explanations of what he is doing are delivered in a slightly hesitant and even seemingly self deprecating manner which completely fails to obscure the steadfast determination to go further which imbues his every word. There is no thought of calling it a day, even at the age of ninety years and even despite his physical handicaps. Cézanne wanted to die painting: one feels that Michael has this same level of commitment.
The purpose of this Post is to provide the link below to “The perception of surface”, Chapter 7 of my book “Painting with Light and Colour”. This provides illustrations and explanations of ways we perceive: (a) reflected light as opposed to transmitted light, (b) matt surfaces as opposed to glossy ones, and (c) the complexities of interreflections. Apart from their intrinsic interest, the function of these in the book is to prepare the ground for the next chapters, which explain how Georges Seurat’s ideas about “painting with light”, either directly or, more often, indirectly, were to revolutionise the use of colour in paintings in a multiplicity of ways. Thus, the next Post will provide a link to Chapter 8, which, after introducing Seurat’s ideas and methods, starts the process of going more deeply into their game-changing ramifications. What follows below gives a foretaste of the nature of these.
Not nearly enough importance is given to the impact of Georges Seurat’s ideas concerning the depiction of reflected light. Their significance lies in the fact that, either directly or indirectly, they were to have a transformative, game-changing influence on the way later artists:
Painted reflected light.
Approached the depiction of illusory pictorial space.
Explored whole-field colour relations.
Ramped up the colourfulness of their paintings.
Too often in the past the focus has been on Pointillism as a method, treating it as a fascinating, but not so very important phase in art history. In contrast, in my book, I show that the ideas behind Seurat’s innovations, as developed and transformed by his successors, were to open up possibilities of permanent value for anyone who makes paintings of virtually any kind. With hindsight we can see that Seurat’s ideas:
Furnished one of the two pillars that underpin the transformative use of colour found in the work of numbers of progressive artists, including Gauguin and Bonnard. As we shall see in later chapters, when we come to the subject of whole-field colour relations, the artist primarily responsible for the other pillar was Cézanne. It was these two sets of ideas that were to be synthesised in the dogmas of Marian Bohusz-Szyszko.
Opened the way to scientific experiments that supplied coherent insights into the working principles of the eye/brain systems that enable the perception of surface-solidity, surface-form, in front/behind relations and the qualities of light (reflected light and ambient illumination). Since it is the operation of these that make possible the only way that artists can use colour/lightness relationships to deceive viewers into interpreting the content of paintings as existing in illusory pictorial space, it is hard to exaggerate the practical value for painters wishing to represent any of the above mentioned qualities in their work.
To prepare for grappling with all this, it is helpful to be clear about the role that the light reflected from surfaces has in creating our sense of their solidity and our perception of both their form and their interconnectedness.
Chapter 1 of my book “Painting with Light and Colour” told of the dogmas of Professor Bohusz-Szyszko and his claim that they were “all you need to know about painting”. It also praised their value as a practical guide.
Chapter 2 is about doubts that arose concerning their theoretical basis. It was the experience of living with these that prepared me for a critical moment in my life. This came several years later while I was reading an article in the Scientific American that had been brought to my attention by one of my colleagues in the Psychology Department at the University of Stirling. The purpose of the article was to present what the author, Edwin Land, fervently believed to be a mould-breaking understanding of the neural computations used by the eye/brain to produce the phenomenon of “colour constancy”. Actually Gaspard Monge, a French mathematician, had beaten him to the post by nearly two hundred years. But this did not stop the contents of Land’s article from being the catalyst to the evaporation of my worries. More importantly, my efforts to better understand the significance of Land’s ideas were eventually to open the way for cooperations with colleagues in the The University of Stirling Vision Group (see link below*). Without their help, few of the new insights relating to the use of colour in paintings that can be found in my book would have materialised.
But this is jumping the gun. First click on the link below to access the chapter on the doubts that had haunted me and on the process of questioning they set in motion. Its function is to explain why there is a need for the new ways of thinking and doing that play such an important part in the chapters that follow.
*Above and in many places in my books, I acknowledge the importance of the role of colleagues in the development of the new science-based ideas put forward in them. As well as acknowledging the help of various individual scientists at the University of Stirling, I call attention to the role played by the University of Stirling Vision Group. For more on this pleaseclick here to access the Post I have written on its personnel and its activities.
Posts relating to other chapters from “Painting with Light and Colour”: