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I’ve found that one of the most useful concepts to keep in mind while retouching my images is what I like to call “shadow theory.” It’s a basic concept used in drawing and painting. Simply put, it states that all shadows begin with what is called a “form shadow,” and end with what is called a “cast shadow.”

Depending on the size and direction of your light source, both types of shadows can either be more or less defined. A large light source will give smoother form and cast shadows. For this post I’m using an image with hard light, in order to differentiate between the two types of shadows. The theory, however, is the same no matter what type of light source you use.

Form shadows

Form shadows consist of a softer transition that defines the form of the subject. By either increasing or decreasing the size of the transition you are able control the angularity of the form. You can either:

• make it rounder by increasing the size of transition zone
• make it more angular by decreasing the size of the transition zone

Cast shadows

Cast shadows are a projection on the subject. I rarely manipulate the cast shadows, as they typically have little impact on the dimensionality of an image; sometimes their shape is awkward and I will liquefy them a bit, but I rarely find it useful to alter the transition zone of cast shadows.

Here are some additional points to keep in mind when manipulating your shadows:

• The texture of any given surface will be more prominent within the transition zone of your form shadows. To be more scientific, the texture of any given surface will be maximized exactly one halfway between the full highlight and the full shadow, when the light source is at 90 degrees to the plane of the subjects’ surface. For retouching this means that in order to create the appearance of even skin texture you will need to spend more time within the transition zones of you form shadows. This is the area where hairs, pores, zits and facial features really begin to pop out.
• You can use the transition zone of your form shadows as a guide for you dodging and burning. Do your dodging and burning while zoomed out, and work with the intention of increasing dimensionality (creating a smooth form shadow) while eliminating unwanted texture. I see a lot of images where the removal of unwanted texture is achieved at the cost of dimensionality, which results in a flat looking image.
• By bumping form shadows one direction or another you can alter shape. Sometimes the bumping comes in the form of the liquefy tool, but it can also come in the form of dodging and burning. I have seen plenty of images where cheeks, jawbones and noses have been totally reconstructed with nothing more than careful dodging and burning. Change the shadows and you change the shape.