Reilly uses the term gradation to describe a gradual change in value over a flat surface; side to side, top to bottom or diagonally, notably on the background. It is a minor effect of light and can help show the position of the light source, and how far the subject is from the background.
|The nearer the light source to the background, the greater the degree of gradation.|
Keep the degree of change modest, or the background will begin to look three-dimensional and detract from the form of the subject. Think of gradation as both a natural effect and a design element.
Progression: This term describes the degree of change in a form as it progresses out from the picture plane towards the viewer or recedes away from the viewer. The greater degree of change, the more attention it will receive, and the more it will appear to project toward the viewer. Conversely, the lesser degree of change the more the object will seem to recede. Hard edges help an object project, soft edges help it recede. High value contrast help it to project, minimal contrast helps it to recede. Reilly emphasizes that the changes in value should be made to the object, not the background.
© John Ennis 2011
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