THE RETINAL IMAGE versus THE IMAGE-IN-THE-VIEWFINDER
How the eye and brain function is very complicated and is not fully understood.
Writers about the French Impressionists often mention the image on the retina, and describe the Impressionists as having aimed to replicate this image. However, as Gombrich showed in Art and Illusion (1956) there are many problems with this theory. Gombrich proposed to substitute for it his theory of the ‘Eye witness’. An accurate painting does not so much imitate the image on the retina, as provide no false information about the scene in front of the eye. For example, it one thing overlaps another when seen from the painter’s viewpoint, it would do the same in the painting. So what appears on the picture plane is what concerns naturalistic painters, rather than the image on the retina. The picture plane can be recorded, but the image on the retina is far too changeable and fugitive to form the basis for a painting.
In contrast, the generation of the image-in-the-viewfinder is relatively easy to understand. The eye and brain are not involved in this image because it is purely a matter of geometry – a record of a pattern of light. If the viewer, subject, and pane of glass are all stationary, the image on the glass can be one size, and one size only. The camera image is very similar to this, except that its scale is not defined in the same way. The photographic image may be scaled to any size.
It is often said that the Impressionists aimed to replicate the retinal image (though I have not been able to find a direct quote about this from any of the Impressionist painters). According to writers, the Impressionists were imagining that the eye worked much as a camera, and that the image on the back of the eye, would just like the image inside a camera,
This idea is simplistic. It is a variant of the Bucket theory – the idea that the eye collects sense-data, then sends it to the brain, which in turn processes the data. The aim of the Impressionist was to collect only the sense-data, and to eliminate the processing done by the brain – to see only patches of colour, not the objects which gave rise to those patches.
However scientific studies have shown that this account of how the eye and brain work is incorrect. The eye largely collects only what the brain tells it to look for. A motorist who is on the lookout for motor-cars can quite easily fail to notice cyclists and crash into them. The light from the cyclist may have entered the motorist’s eye, but it did not reach the brain because the brain was not primed to look for it.
What the Impressionists actually did had little to do with the retinal image. It was much more like what the artist in Durer’s illustration was doing. Matching patches of colour as they appear on a picture plane.
Gombrich’s Art and Illusion explores this subject in great depth. Here are a couple of quotations to give an idea of his approach:
Gombrich:
Art and Illusion, 1959
When Bernard Berenson wrote his brilliant essay on the
Florentine painters, which came out in 1896, he (wrote) “The painter can accomplish his task only by giving tactile values to retinal impressions.”
We remember that the ideas about perception on which Ruskin built with such confidence, and artistically with such success, had been propounded more than a century earlier by Bishop Berkeley in his New Theory of Vision in which a long tradition had come to fruition: The world as we see it is a construct, slowly built up by every one of us in years of experimentation. Our eyes merely undergo stimulations on the retina which result in so-called “sensations of colour.” It is our mind that weaves these sensations into perceptions, the elements of our conscious picture of the world that is grounded on experience, on knowledge.
Art and Illusion Chapter IX
Given this theory, which was accepted by nearly all nineteenth-century psychologists and which still has its place in handbooks, Ruskin’s conclusions appear to be unimpeachable. Painting is concerned with light and colour only, as they are imaged on our retina. To reproduce this image correctly, therefore, the painter must clear his mind of all he knows about the object he sees, wipe the slate clean, and make nature write her own story— as Cézanne said of Monet: “Monet n’est qu’un oeil — mais quel oeil!” (Monet is only an eye, but what an eye!)