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I attach a further improved version of the algorithm of Messrs Slime and
Hughes. It now scales correctly for any camera angle and can use any
arbitrary vignetting function. There are built-in calibration objects to
verify the simulation.
/*-- Validating the algorithms for vignetting in the camera lens-----.
The earlier model by Hughes, based on a suggestion by Slime, and which is
the basis of this present file, did not scale correctly. Vignetting did not
occur outside the cylindrical region defined by the texture. So, I drilled
a hole in a very thin black box with the inverse of the textured sphere and
filled the hole with the textured sphere.
There's a series of sphere objects and a pair of boxes in a rectangular
scene geometry to test the vignetting code. There are three types of
vignetting
functions built into this file for illustration purposes:
(1) a linear function of the radial distance, to keep it simple to
measure in PaintShopPro the accuracy of the vignette.
(2) a sqrt(cos) function
(3) a cos^4 function ( which is the brightess of an image created by a
pinhole lens without vignetting!) In this case the image is rendered as
a
16bit height field....but is only realistic for a 180deg field
*/
#declare VigFunc = 2;
global_settings { assumed_gamma 2.2
#if(VigFunc = 3) hf_gray_16 #end
}
#declare CamHfov = 50; // Horizontal field of view of camera..select
to your choice
#declare CamLocn = -z*50; // Camera location..but only along the z axis
in this file
#declare Steps = 24; // Counter for number of steps in vignetting
'pigment' (up to 254 )
#declare VigTex = texture { pigment { cylindrical
color_map { #declare Rho = 0;
#while (Rho <=1)
#declare LookAng =
Rho*CamHfov/2;
#switch (VigFunc)
#case(1) #declare
TRho = 1-Rho; #break
#case(2) #declare
TRho = sqrt(0.5*(1+cos(pi*Rho))); #break
#case(3) #declare
TRho = pow(cos(pi/2*Rho),4); #break
#end
#if(TRho<=0) #declare
TRho = 0;#end
[ Rho color rgb 0
transmit TRho]
#debug concat("
",str(TRho,19,6),"\n")
#declare Rho = Rho +
1/Steps;
#end
}
frequency -1 rotate 90*x
}
finish { ambient 0 diffuse 0 }
}
#declare VigSfr = sphere { 0,1 texture { VigTex } }
#declare BoxwitHole = intersection { box {<-1e6,-1e6,-0.1>,<1e6,1e6,0.1>}
sphere { 0,1 inverse }
pigment { rgb 0 } finish { ambient 0
diffuse 0 }
}
#declare MicroScale = 0.001;
#declare Vignetter = union { object { BoxwitHole }
object { VigSfr }
scale MicroScale translate
CamLocn+z*MicroScale/tan(radians(CamHfov/2))
}
object { Vignetter }
#declare ObjTex = texture { pigment { rgb <1,1,0> } finish { ambient 1
diffuse 0} }
#declare VboxScale = 0.999*abs(CamLocn.z)*tan(radians(3/4*CamHfov/2));
#declare Vbox = box{<-1,-0.005,0.01>,<1,0.005,0.02> scale VboxScale
texture { ObjTex } rotate z*90}
object { Vbox }
#declare HboxScale = 0.999*abs(CamLocn.z)*tan(radians(CamHfov/2));
#declare Hbox = box{<-1,-0.005,-0.01>,<1,0.005,0.01> scale HboxScale
texture { ObjTex } }
object { Hbox }
#declare Ipos = -1;
#while ( Ipos<=1)
#declare Spos = x*tan(radians(CamHfov/2*Ipos))*CamLocn.z;
sphere { Spos,0.02*HboxScale pigment { rgb <1,1,0> } finish { ambient 1
diffuse 0 } }
#declare Ipos = Ipos + 0.1;
#end
plane { z,1 pigment { checker color rgb 1 color rgb 0.5 translate
<1,1,0>*0.5 scale 0.2*CamHfov } finish { ambient 1 diffuse 0 } }
background { rgb 1 }
camera { #if(CamHfov >= 90) ultra_wide_angle #end
location CamLocn up y right x*1.33 look_at 0 angle CamHfov
}
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