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18556Re: [PanoToolsNG] Re: White (Neutral) Balance in Panoramas

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  • Georgia Real Tours
    Mar 8, 2008
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      On 3/7/08, johncharlesriley <johnriley@...> wrote:
      > >
      > > Using black velvet this way is a very clever trick. What happens, I
      > > believe, is that the "gray" appearance is caused by a myriad of
      > > specular reflections from the surfaces of the fibers. Specular
      > > reflections are always non-colored, so indeed this method should
      > > produce a very neutral gray as long as the body of the fibers is very
      > > dark in comparison.
      > >
      > > --Rik
      > >
      > Sorry, I have to jump in here. I am not sure what you might be thinking of, but specular
      > reflections have the same color as the incident light. When you see yourself in a mirror,
      > that is a specular reflection. A specular reflection is simply when light is reflected in a
      > mirror-like fashion from a smooth surface. Examples are the glare off of a car (or water
      > or snow) from the sun. They are problematic because you are seeing a reflection of the
      > sun and not the object itself. Since specular reflections are partially polarized (or
      > completely if at Brewster's angle), polarized sunglasses can drastically reduce their
      > intensity. Then you can see the object itself by the diffusely reflected light, which is
      > scattered in all directions.
      > Sorry for being pedantic, but I am a physics professor and just can't help it 8-) Now, what
      > else might be going on with the fibers of black velvet, I don't know, but it could be
      > interesting to hear.

      Exactly. The grain of the fabric acts as a rudimentary polarization
      filter. Further, since it is diffuse, the light reflected is a
      culmination of the ambient light in the room. The average of all
      those random specular reflections is what is sought.

      But you knew that and were just testing us! Very tricky, Mr. Riley,
      but it's turtles all the way down!



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