Pixiq

The camera and the retina see the same luminance in an image, which is a combination of reflection (in the words of Land, “the language for delineating objects”) and illumination (“the language for displaying illumination”). The visual cortex in the rear of the brain processes this luminance signal from the retina, separates reflection and illumination, and recombines them in a very special way to show us the world as it truly is, visually. The brain first detects edges, separating those edges into illumination edges and reflection edges. Then, it uses complicated algorithms to process the image into our perception of luminance, called luminosity or brightness. This is an important point, and bears repeating: Be mindful of the difference between actual luminance and our perception of luminance, called luminosity. An unprocessed image direct from the camera is a straight luminance image, hence the disparity between what we visually perceive and what we get in a photograph.

What painters have been able to do since the invention of chiaroscuro is to “fool” the observer’s eye by taking a straight luminance image and adding elements of visual perception to the canvas to create that artist’s subjective interpretation of luminosity. So, painters are involved in a secondary process that most photographers don’t ever go through, except, as Land hints, in the greatest masterpieces, which have been dodged and burned extensively (a form of secondary processing that, when done well, mimics this secondary step that painters employ).

John Sexton, a contemporary master printer in traditional black-and-white silver photography, uses a very complicated burning and dodging procedure that mimics what the painters do to a canvas. The black-and-white photography masters (such as Ansel Adams, Minor White, and Gene Smith) also burned and dodged in very complicated ways. Someone once asked Gene Smith how he made a print and he replied, “I go into the darkroom in the morning with a gallon of Dektol in one hand, a package of 11x14 Polycontrast J under my arm, and a fifth of scotch in the other hand, and come out twelve hours later with a print.”

Great photographers are able to transform the raw luminance of the captured image into something that expresses their own unique perception of the world. Learning this skill of transforming luminance into luminosity takes time and practice. In terms of our discussion, changing luminance into luminosity is creating what lightness perception scientists call “good constancy.” We, as artists and photographers, recognize that as presence. Visually, here’s how the luminance problem (the “gaggle of voices”) presents itself:

In looking at these images, you can see how the reflection image and the illumination image combine into luminance. The result looks startlingly lifelike until you compare it to the luminosity image. This set of images illustrates the difference between what we think is real (the image direct from the camera) and the image as it is processed through visual perception. This is the difference between luminance and luminosity, respectively. What we get from the camera needs that secondary processing step for it to look like what we visually perceive and feel. The following image sets are some real photographic examples of this process.

The first image in each set is a RAW file converted to black and white in Adobe Lightroom software using the grayscale button in the Develop module. These initial grayscale images are otherwise unprocessed, and they represent a basic luminance image. The second image in each set was converted in Adobe Photoshop using the PercepTool plugin. The differences you see in each pair will depend upon the inherent depth and tonal spread each has to begin with. For this reason, the effect of the PercepTool plugin is more pronounced in some of the luminosity transformations.

What are depth boundaries?

Our eyes communicate information about depth to the brain through identification of depth boundaries in the world around us. To illustrate this, hold up a hand in front of you. Now place your other hand directly behind it so they are touching. Using depth perception, our eyes recognize that one hand is closer than the other. The depth boundary is the place where the two hands meet—the point at which the depth changes.