Diffusion

Let's look at some real world examples.

The ball on the left is made of a very soft rubber. It appears to be smooth but like a lot of rubber the surface material is pliable and rough on a molecular level. This is not only what gives the surface of rubber extra friction but also what causes light to scatter more. Any given ray of light that hits the surface will be reflected but not necessarily in a similar direction to rays right next to it.

This pool ball has a smoother, harder surface than the rubber ball but is not as reflective as some kinds of metal or glass could be. This is because the material of the ball is made of up a substance that actually allows light to penetrate and diffuse just below the surface. This produces the effect of a surface that is both reflective and diffused at the same time.

This ball is completely reflective. Not only is the surface very smooth but individual molecules are packed in a way that produces a more uniform surface. All rays of light that hit the surface will bounce in a way appropriate to the angle of the surface. This produces the almost perfect reflection of the world around it.

Colored lighting

Generally you do not want to use pure white and black to add highlights and shadows to your image.

While it can take quite a while to get used to doing it by memory - it is also an invaluable skill to know how different colors of light can interact with different surface coloring.

Let's look at some rules (They're more like guidelines) for painting with colored light.

  • Light that is the same color as the surface intensifies the saturation.
  • Light that is complementary to the surface produces "muddy" or "grey" colors.
  • Light that is a different color than the surface, but NOT complementary, will "pull" the surface color towards it on the color wheel.

Keep in mind that what we describe as the "surface" color is not the same as the "visible" color. The surface color describes the actual color of the object regardless of what the lighting conditions are while the visible color is what the viewer currently sees.

If you own a white shirt and stand under red light anyone looking at you will see the color red but that doesn't change that the shirt is white.

Observe the picture below. Imagine that it is a series of colored bars, it doesn't matter what the material is, in an evenly lit room using only white light. Since we are using *white* light we are pretty much seeing the surface color of the bars as they really are.

Now observe the same scene under different light below. We've turned off the white light that was cast upon all of the bars and have turned on several differently colored lights that are casting light out of the slits in the wall at the top of the image. The left most slit is casting white light while the others are casting colored light of various hues.

This image has been made using 3D software to try to create as "pure" of an example as possible with no atmospheric distortion of the scene. It shows what happens when different hues of radient light fall upon different hues of surface color. Notice that it almost creates a "chart" wherein we can see a repeating pattern in the way the different mixtures of light and surface color behave.

Notice that when a color of light is cast upon a surface of a similar color is when the visible color is at its most vibrant. The red light on the red surface produces the brightest and most saturated red, the green light on the green surface produces the brightest and most saturated green, and so on and so on.

At the same time there are some visible colors that become very muted, almost grey, even though we are aware that both the surface and the light are of a strong color.

This is not accidental, and there is a very reproducable method to know when this is going to happen.

Compare the grid of light you see here with the color wheel. This is a wheel of *additive* light.

Where complimentary colors from the wheel (colors that are directly opposite from each other on the wheel such as green and pink) meet on the grid they result in the most grey visible color. Colored light cast upon a complimentary surface color results in a desaturated visible color.