As a visual sign, a photographic image usually represents an object or a scene; this is the habitual way of seeing it. But it accomplishes that common semiotic task by representing various formal features of the object or scene: its color, shape, texture and spatial distribution of light. The curious fact is that photography does this in very different ways. With respect to color, a pigmented object produces a certain spectral distribution of light, and an ordinary photograph of that object causes approximately the same spectral distribution. The pigmented emulsions of the photographic paper act upon light in the same way as the pigmentation of the objects. In this sense, photography represents color by sharing physical properties with the objects. In truth, instead of representing color, it reproduces color. We have an indexical aspect of photography here (an index being a sign that is physically connected to the object that it represents). This is quite different from what occurs with the representation of the spatial distributions of light (transparency, translucency, mirror-like appearance, gloss, matt quality, etc.) by photography. A glass of water is a physically transparent object that generates the visual sensation of transparency, but a photograph of that glass, being an opaque object in itself (the substratum is an opaque piece of paper), also conveys the sensation of transparency. Summing up, photography represents the spatial distributions of light not by sharing physical features with the objects, but by means of a transformation that brings about a certain kind of similarity. In this sense, we could speak of iconicity (an icon being a sign that refers to its object by means of some kind of similarity with it). This paper will present a survey of these and other semiotic categories involved in photography when representing color and the perceived spatial distributions of light.
José Luis Caivano, "The Representation of the Visual World in Photography" in Proc. IS&T CGIV 2008/MCS'08 4th European Conf. on Colour in Graphics, Imaging, and Vision 10th Int'l Symp. on Multispectral Colour Science, 2008, pp 189 - 193, https://doi.org/10.2352/CGIV.2008.4.1.art00041