Maris,
The relationship between photon arrival and silver deposition, for example, is not simply a 1:1 product .....
Asher
Forgive the following convoluted disquisition. I got taught Norbert Wiener's
Cybernetics and Claude Shannon's
Information Theory in my youth and I'm a bit trapped in that way of thinking. Doug Kerr will know what I mean.
There are several relationships between photon arrival and silver deposition. There may be more silver deposited or less. The size of the silver grains may be small and result in a brownish image. The grains may be large and the image is bluish. But these observations do not at all touch on the fundamental promise carried by pictures made out of light-sensitive materials using traditional methods.
Here's unique line of thought. It answers the question in lens-based picture-making of why a picture of a tree (say) is not like a tree. The subject matter of such a picture is not the tree at all. The subject matter is actually the
real optical image of the tree that floats in the back of the camera or eye. It is this real optical image that penetrates a retina, a megapixel sensor, or a light sensitive surface and leads ultimately to a picture coming into being. And what of the poor original tree? Well, it
is subject matter but only for it's optical image not further. More generally, if picture-making is the result of a causally linked chain of events then each event is subject matter for the result that follows it. Is that too abstract?
A real optical image is an electromagnetic field that usually varies (sometimes beautifully) from point to point. If one immerses a light sensitive substance in the field then that field and the substance become physically co-mingled. They occupy the same place at the same time. Every single point in the field corresponds uniquely to a single point in the light-sensitive substance. Of course in practice one chooses light-sensitive substances that will firstly be changed by the field, and secondly the changes will remain after the field is removed. The resultant pattern of changes is a unique point by point map of the scalar values of the field during the time it inter-penetrated the light-sensitive substance.
The light-sensitive substance that starts off blank and ends up bearing the pattern of light-induced changes
is the picture. Sometimes the changes are immediately visible and the picture may be removed from the camera and inspected directly. Sometimes the changes are made visible by a development process which reveals but does not reorganise the pattern.
The fundamental promise conveyed by pictures made out of light-sensitive substances is that there is a one to one correspondence and causal relationship between
places in the picture and
places in the real optical image. The correspondence, image pattern to picture pattern, is mandated by the laws of physics and chemistry and not by the whim of the picture-maker.
Making pictures out of light-sensitive substances is severely limiting. Only those things that exist and interact with light can be depicted. I personally like the authenticity and austerity of this approach. But many more things can be imagined than seen and the arts of painting, drawing or electronic image-making have much work to do.