Visual Rhetoric Class, see drupal site.
We expect images to relay some kind of truth. Whether it is a graph or a picture, there are certain qualities that they possess to portray the highest level of truth. This is the modality of the image. “Each realism has its naturalism, that is, a realism is a definition of what counts as real, a set of criteria for the real, and it will find its expression in the “right”, the best, the (most) “natural” form of representing that kind of reality, be it a photograph or a diagram.”
In their book Reading Images: The Grammar of Visual Design, Kress and van Leeuwen identify eight markers that help determine the modality of an image: color saturation, color differentiation, color modulation, contextualization, representation, depth, illumination, and brightness. They define the following as,
“Color Saturation, a scale running from full color saturation to the absence of color, that is to black and white.
Color differentiation, a scale running from a maximally diversified range of colors to monochrome.
Color modulation, a scale running from fully modulated color, with for example, the use of many different shades of red, to plan, unmodulated color.”
These are the three markers that deal with color. It is important to realize that high scales of all these will dilute the truth to the image by created a mess of colors; the message will be extremely distorted.
“Contextualization, a scale running from the absence of background to the most fully articulated and detailed background.”
“Representation, a scale running from maximum abstraction to maximum representation of pictorial detail.”
“Depth, a scale running from the absence of depth to maximally deep perspective.”
“Illumination, a scale running from the fullest respresentation of the play of light and shade to its absence.”
“Brightness, a scale running from a maximum number of different degrees of brightness to just two degrees: black and white, or dark grey and lighter grey, or two brightness values of the same color.”
Kress and van Leeuwen basically argue that any extreme of their particular modality sub-catagories will cause the believability of an image to suffer. For example, too much color saturation or too much brightness cause an inharent dissonance that conveys a sub-reality. However, all their catagories have a "Mid-range" and this is where the believability of an image is strongest.
Kress, Gunther and Theo van Leeuwen. Reading Images: The Grammar of Visual Design. London: Routledge, 2001.