hughes, b. wrote:
>"Slime" <slm### [at] slimelandcom> wrote in message
>news:3e442587[at]news.povray.org...
>> > Does anyone know how to simulate the vignetting that was present in old
>> > camera lenses - a loss of brightness towards the edge of the field, say
>> > according to a cosine law?
>>
>> Simple solution: put a sphere around the camera, textured with a
>cylindrical
>> texture (so the values you give in your color_map correspond to the cosine
>> of the angle), using colors of rgbf<?,?,?,1> where the ? goes from 0 at
>the
>> edges to 1 in the center.
>
>I'll try to expand on this and use transmit, and not filter, as the variable
>and rgb 0 for the color. However, when I try the cos-4th law as I just found
>it (not knowing of it before) I can't seem to get POV-Ray to produce the
>same result for cos(A)^4 by using pow(cos(A),4). Am I doing that wrong? For
>example, I find cos(20/2)^4 in a calculator to be
>0.94060186578282644642735371998179 and yet in POV it is 0.495673773. Maybe
>the order in which the operands work causing the discrepency? Although I
>don't see how that could be the reason at all.
>
>Here's the test scene I was messing with:
>
>// my lame attempt at lens cos 4th law, not meant to be used as a totally
>working concept
>
>#declare A=67; // angle
>#declare R=<10,0,0>; // orientation
>#declare L=<0,0,-5>; // location
>#declare V=20; // variable, degrees? divided in half later
>
>camera {
>  location  0
>  look_at   z
>  angle A
>  rotate R
>  translate L
>}
>
>sphere {
>  0, 1
>  texture {
>    pigment {
>      cylindrical
>      color_map {
>        [0 color rgb 0 transmit 1 ]
>        [pow(cos(V/2),4) color rgb 0 transmit pow(cos(V/2),4) ]
>        [1 color rgb 0 transmit 0 ]
>      } frequency -1 rotate 90*x
>    }
>    finish{
>      ambient 0 diffuse 0
>    }
>  }
>  scale 0.0001 // make small/invisible
>  rotate R
>  translate L
>}
>
>#debug concat(str(pow(cos(V/2),4),-1,9))
>
>sky_sphere {
>  pigment {
>    gradient y
>    color_map {
>      [0 rgb <0.7,0.8,0.9>]
>      [1 rgb <0.2,0.5,0.8>]
>    }
>  }
>}
>
>light_source {
> <-30, 30, -30>,1
>}
>
>// ----------------------------------------
>
>plane {
>  y, -1
> pigment {color rgb 1}
>}
>
>sphere {
>  0.0, 1
> pigment {color rgb 1}
>}
>
Dear Mr.Hughes,

Rereading the missages I see that I have incorrectly attributed to SLIME
himself  the pov file elaborating SLIME's suggestion concerning a solution
to the question.  Please accept my apologies - and I hope you enjoyed my
modest extension to your elegant solution.

I find it strange that the messages are printed in reverse order - I expect
to see the latest at the top of the list...anyway, thanks again.

Yours,

Don Barron

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