Understanding light: Surface Appearances

Surface Appearances

All surfaces produce diffuse, direct, and polarized reflection in varying degrees. We see all of these reflections, but we are not always conscious of them. That is because of our brain.

Psychological image vs photo-chemical image

The psychological image in the brain may be quite different from the photo-chemical image the eye actually sees. Psychologists have not completely explained why this difference exists. Movement certainly has something to do with it, but not  everything. Some visual defects are less disturbing in a motion picture than they might be in a still photograph, but not much… Photographers know that the brain cannot edit an image of the scene as well as the scene itself. We discovered that fact when we learned how quickly we could spot defects in our images, even though we could not see them at all when we carefully examined the original scene.

When we photographers make a picture we have to consciously do some “editing” onto the “original scene” that other observers do unconsciously.

Photographer as an editor

Photographic lighting deals mainly with the extremes: the highlights and the shadows. When we are happy with the appearance of these two, we are likely to be pleased with the middle range also. Highlight and shadow together reveal form, shape, and depth. But highlight alone is usually enough to reveal what the surface of an object is like.

All surfaces produce both diffuse and direct reflections and that some of the direct reflections are polarized. But most surfaces do not produce an even mix of these three
types of reflections. Some surfaces produce a great deal more of one than another. The difference in the amounts of each of these reflections determines what makes one surface look different from another.

One of the first steps in lighting a scene is to look at the subject and decide what kind of reflection causes the subject to appear the way it does. The next step is to position the light, the subject, and the camera to make the photograph capitalize on that type of reflection and minimize the others.

When we do this we decide what kind of reflection we want the viewers to see. Then we engineer the shot to make sure they see that reflection and not others.


Capitalizing on Diffuse reflection

Photographers are sometimes asked to photograph paintings, illustrations, or antique photographs. Such copy work is one simple example of a circumstance in which we usually want only diffuse, and not direct, reflection.

Diffuse reflection gives us the information about how black or how white the subject is. Because diffuse reflection can reflect light frequencies selectively, it also carries most of the color information about the subject. However, notice that diffuse reflection does not tell us very much about what the surface material is.

  • How to photograph diffuse reflection:
    • Because we want only diffuse reflection, we place the light anywhere outside the family of angles.
    • understanding_light_004_capture_diffuse_reflection_1
    • For more illuminated, multiple lights can be used.
    • With this setup, we can get flare-free images.
    • The closer the light source is to the subject, the more directly it lights the subject and the more even the illumination becomes.


Capitalizing on Direct reflection

In case diffuse reflection doesn’t work, we have to use direct reflection. This usually reveal texture of the surface.

  •  How to photograph direct reflection:
    • understanding_light_004_capture_diffuse_reflection_1
  • Using the lighting diagrammed to maximizes direct reflection and reveals texture in the leather:
    • understanding_light_006_capture_direct_reflection_2


Competing Surfaces

Some surfaces are rendered better by capitalizing on diffuse reflection; others
are depicted best by capitalizing on direct reflection.

  • Direct vs. Diffuse reflection lights (diffuse is better):
    • understanding_light_006_capture_direct_vs_diffuse_reflection_1
  • Diffuse vs Direct reflection light (direct is better):
    • understanding_light_006_capture_direct_vs_diffuse_reflection_2
  • Too often, however, some parts of the scene require diffuse reflection, whereas others need direct reflection. In many of these cases, we can simply deal with the more important part of the scene. If we get that right, viewers do not notice minor defects in the lighting of the rest of the surface. On other occasions, however, several
    entirely different parts of the surface are all important, and those different parts of the picture absolutely must have different lighting.
  • Commercial photographers sometimes work out the composition of a photograph before beginning to perfect the lighting. After all, if the relationship of the angles between the light, the subject, and the camera is critical, it makes no sense to carefully position the light before knowing the orientation of the subject.


Complex surface

Complex surface to mean a single surface that requires both diffuse and direct reflection to define it properly.

  • For example: Glossy wood is a good example. Only direct reflection can tell the
    viewer that the wood is glossy, but diffuse reflection is essential to reveal the color and the grain of the wood beneath the gloss.
  • Glossy wood:
    • complex-surface-1
  • Lighting diagram to produce both the direct and the diffuse reflections:
    • complex-surface-lighting-diagram
  • Adding an additional three-dimensional subject to this kind of scene often makes
    the lighting easier. For example: the glasses add a three-dimensional element, which provides additional visual clues (the reflection of the glasses) to prove the wood surface is glossy:

    • complex-surface-add-3d-subject



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