The other constancies

My two previous  the Posts provided links to Chapter 12, “Local colour interactions” and Chapter 13, “Colour constancy”, from my book “What Scientists can Learn from Artists”. This Post provides a link to Chapter 15, “The other constancies”. Below the two images you will find an edited version of the “Introduction” to this chapter. As with other Posts, if you find that the subject matter interest you, you can click on the link below to the .PDF version of the chapter as a whole. The images illustrate two of the visual perceptual problems with which artists have had to come to terms.

Cézanne read Helmholtz and took the view that perceived reality is different from the measured reality that his predecessors sought to depict. When he tipped up landscapes and the tops of pots and vases it was because he believed that he was painting what he saw, even if he had to cheat to do so.


Introductory to Chapter 15

Colour constancy is by no means the only constancy of visual perception. There are many other constancies and all are fundamental to the ability of the eye-brain to make practical use of visually acquired information. Paradoxically, although their name suggests stability, they are responsible for the veritable “shifting sands of appearance” which, in its various guises, constitutes one of the main problems for artists seeking to obtain accuracy in drawings or paintings from observation. This is because they ensure that, when we look separately at any two similar features of appearances whether they be whole objects, parts of objects, sections of contour or colours, there is a very strong tendency to see them as being more similar to one another than objective measurement would dictate – often a great deal more so. Our visual systems upset the measured parameters of external relationship by relentlessly forcing them towards normative dimensions and values. As a result, the constancies involve enlarging and diminishing, squashing and stretching, revolving, darkening and lightening and modifying colour. Any list of the constancies of particular interest to the artist should certainly include (a) size constancy, (b) shape constancy, (c) orientation constancy (d) lightness constancy and (e) colour constancy.






Related chapters from “What Scientists can Learn from Artists”

Other Posts on colour and light in painting:

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local colour interactions

Introduction to the Post on “local colour interactions”

This Post is the second that offers a link to a .PDF version of a chapter from “What Scientists can Learn from Artists”. The purpose of making this more scientifically oriented information available on this website is to encourage readers to go deeper the ideas presented in my practice-oriented books on drawing, painting and creativity (see “Contents List” on the “Posts Page”). Chapter 11, the chapter featured here, focuses on new and unfamiliar things of potential value to artists that can be said on “local colour interactions”, a subject that has featured widely both in books and in the classroom. Its father figure is Eugene Chevreul, the Chemist at the Goblin tapestry works, who was responsible for the phrase “simultaneous colour contrast”,  and the best known publications on the subject are by Johannes Itten and Joseph Albers, both teachers at the Bauhaus. Of more recent books covering the subject, I can recommend “Colour : A workshop for artists and designers”, by David Hornung.

With so many authoritative writings on the subject, it might be supposed that I would have little to add, particularly since, as a general policy throughout my books, I have done my best to avoid wasting time on subjects that have previously been exhaustively covered in convincing ways. It is for this reason that my chapter on “local colour interactions” concentrates on subjects that do not appear in the publications of Chevreul, Itten, Albers, Hornung or, as far as I know, of anyone else. What I have to say is based on research triggered by the excellent teaching I received at my art school and issues arising in my own paintings. Its novelty comes either from original or less well know scientific research that deals with matters of potential interest to artists.


local interactions
Figure 1 : Nine discs contrasted with different coloured backgrounds, based on an Art School project that not only raised many questions but also triggered further investigations in the context of my own painting.


The link to the .PDF file




colour contrast
Figure 2 : An illustration from a children’s book that led to an interest in colour interactions involving thin lines and over time to a number of surprising discoveries


Other chapters from “What Scientists can Learn from Artists”

These deal in greater depth with subjects that feature in the volumes on the practice of drawing, painting and creativity.

Published chapters from book 2 of “Painting with Light and Colour”:

That is to say, the one that focuses on issues relating to local colour interactions, as opposed to how reflected-light influences appearances.

Other published Posts on colour and light in painting:

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Colour constancy demonstration

Colour constancy sets the ball rolling

It was unequivocal evidence of “induced colour” and “colour constancy” that triggered the realisation among scientists towards the end of the Eighteenth Century that colour is not a property of surfaces in the external world but phenomenon that is made in the head. Once this idea had been digested, it gained momentum and evidence began to pour in to suggest that all visual experience is a creation of the eye/brain combination. This game-changing paradigm shift was to lead, not only to the birth of the science of “visual perception”, but also to fundamental changes in the practice of artists,  either when drawing or painting from observation or when seeking control of pictorial dynamics. This is why the “constancies” and “simultaneous contrast dynamics” play such an important role in my books on the practice of painting and drawing. It is also an important part of the reason why I have written “What Scientists can Learn from Artists”, the last volume of my four volume series that explains the science behind so many of the ideas elaborated upon in the remaining three volumes. In going more deeply into the subjects that play such an important role in these books about artistic practices, it plunges us deep into the astonishing nature of the working principles of visual perception. Apart from the sheer wonder this must surely generate, knowing about the ways these determine how we “look” and how we “see” should have a significant benefits for artists: The deeper understanding and appreciation of the extraordinary things that are happening in our heads should help artists to:

  • Deal with the many practical problems that invariably face them when drawing or painting from observation
  • Make more creative use of their physical and conceptual tools.

The next Posts I will be chapters from the science volume.

A life changing event

This Post on “colour constancy” is the first from “What Scientists can Learn from Artists”. Its inspiration derives from Edwin Land’s irrefutable demonstration of the phenomenon of “colour constancy”, which proved to be a milestone in the search for an understanding of a subject that turned out to be of key importance to the understanding of how we “perceive surface”, “sense space” and are “aware of of lighting conditions”, all subjects of key importance to the ideas presented in “Painting with Light and Colour”.   

Below are:

  • A photo of the equipment used by Land for his epoch making colour constancy demonstration.
  • A reprise of the “Introduction” to the chapter and a link to a .PDF version of it (no need to read it twice: if you read it below, you can skip it in the chapter)
  • Links to Posts from “Painting with Light and Colour”, all of which (particularly chapters 7 to 11) have a debt to research that grew out of the colour constancy demonstration.


colour constancy demonstration
Figure 1 : The set up for Edwin Land’s first colour constancy demonstration, comprising a multicoloured “Mondrian”, three light sources, projecting the three light primaries, and a telescopic light meter that could take intensity readings from each patch of colour separately.



As explained earlier, a key event in my life was the encounter with Professor Marian Bohusz-Szyszko. The ideas he shared set me off on a lifelong journey of discovery. My first step was to set about testing his seemingly extravagant assertion that it is only necessary to follow two rules to guarantee a good painting:

    • There must be no repetition of colour on the same picture surface.
    • All the colours used must be mixtures containing at least a trace of complementary.

After four years of experimenting, I proved, at least to my own satisfaction, that there is a special quality in all paintings that abide by these two rules. It is difficult to describe, but it involves the creation of a sense of pictorial space and harmony.

Fortunately, a troubling paradox arose that would eventually have a profound effect on the development of the ideas presented in this book. It concerned the Professor’s physics-based proof of the invariable variability of colours in nature. This asserted that no two parts of any surface will reflect exactly the same wavelength combinations into our eyes due to:

    • The complexity produced by the inter-reflecting surfaces
    • Variations in viewing angles and distances
    • Atmospheric filtering

The paradox is that, if the light reflecting from two parts of a surface can never be characterised by the same wavlength combination, how could artists repeat colours on a picture surface? Even if two regions were painted with exactly the same pigment-colour, how could these appear as the same?

Other people might already have known how to resolve this mystery, but for many years I had no idea how to do so. My first inkling of a solution came after many years, as a result of reading a paper by Edwin Land, the inventor of the Polaroid camera. In it was a powerful demonstration of the phenomenon of “colour constancy” and an attempt to explaining it. What the demonstration showed was a region of colour within a multicoloured display (henceforth referred to as the MCD) being perceived as remaining the same, even when the experimenter changed the combination of wavelengths being reflected from it. I was excited because here were two colours being perceived as the same despite reflecting different wavelength combinations into they eyes? For me it was a eureka moment. However a big problem emerged for it was soon clear to me that the explanation of the colour constancy demonstration suggested by Land was not neurophysiologically plausible. An alternative had to be found. I could never have guessed at the treasure trove of discoveries that would come out of my struggles to provide it. This chapter describes Land’s demonstrations in the context of an earlier attempt at explaining colour constancy. The next chapter introduces our neurophysiologically plausible colour constancy algorithm.

The colour constancy chapter




Other chapters from “What Scientists can Learn from Artists”.


Chapters from “Painting with Light and Colour”

Other Posts on colour and light in painting:

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Vision Group acknowledged

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).
  • Leslie Smith * (computing).
  • Bill Phillips * (visual memory and brain function).
  • Karel Gisbers (neurophysiology).
  • Ranald McDonald (statistics and common sense).
  • 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.

*** In 1987 Alistair published:  “a new method of classification” in Pattern Recognition Letters, Volume 6, Issue 1, June 1987, Pages 15-19

****  Fluid Mask: a commercial outcome

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Can we see light?

The simple answer is “no”

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”.




More on Land’s demonstration

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”.

The multicoloured display used by Land as the cover for his 1977  article in the “Scientific American”


Other chapters from “Painting with Light and Colour”:


Other Posts on colour and light in painting:


List of all other Posts

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Scientific revolution gives artists ideas

Five Scientists and a scientific revolution

Strictly speaking a scientific revolution cannot have either a starting point or and end point. It is always part of an ongoing process. However, two events provide milestone contributions to the scientific revolution in the understanding of visual perception that took place in the 18th and 19th centuries. The first was a lecture given by Gaspard Monge in 1789 . The second, the publication of a book by Hermann von Helmholtz in 1867. In between these two dates, various other scientists made key contributions to the science of visual perception. Three worth special mention were Johann Wolfgang von Goethe, Michel Eugène Chevreul and James Clerk Maxwell.

Continue reading “Scientific revolution gives artists ideas”



Below are the contents lists for four interrelated volumes:

1. Drawing (book 1 & book 2)

2. Painting (book 1 & book 2)

3. Creativity   

4. Related Science

A main difference between these volumes and others on the same subjects is that they are strongly influenced by the wide ranging and innovative research undertaken by the author into how artists use their eyes when drawing and painting. spacer


At the bottom of the page, in addition to the chapters from the four Volumes, there are extracts from the ‘Glossary’ (more to be published in the coming months) and a section on “Miscellaneous Subjects” (so far: “A history of Castelnau de Montmiral“, “The University of Stirling Vision Group” and “The Generosity of Genes“).

(Please scroll down to the chapter that interest you, then click to find a link to it, accompanied by introductory material and images)





The chapters so far loaded:


The chapters so far loaded:




Chapters so far loaded


The chapters so far loaded:



          The chapters so far loaded:


The chapters so far loaded, all of which deal with subjects that feature in the other three volumes




Request for comments on the chapters from the books.

I look forward to your comments in the section provided at the bottom of each Post. When you have made them, please leave your email address and tick the box “Notify me of new posts by email.”


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