I commented out the assumed_gamma and the image had the same brightness with
focal blur set to 1 as it did when it was set with 0. Set assumed_gamma to 2.2
for PC systems (UNIX too?). The POV-Ray docs has information on assumed_gamma.
Brendan Ryan

Edward Coffey wrote:

> The scene below renders much brighter when you turn focal blur on (set blur
> to 1), and I'm sure it shouldn't.  Does anyone know the cause?  Here is all
> the information I can muster:
> Computer:  Pentium Pro 200, 32Mb ram
> OS:  Windows 98 and RedHat Linux 6.0 running GNOME and Enlightenment
> POV distribution:  Version 3.1g.msvc.win32 [Pentium II optimized] and
> generic Unix 3.1g built from source to x-povray.
> Other notes:
> assumed_gamma and ambient_light do not seem to be the cause.
> The specific settings of the focal blur do not seem to be the cause, but I'm
> still not ruling out a problem with my scene file.
> There is a gamma correction made at the end of the focal blur function in
> the Unix source (I assume it is there in all the distributions), when you
> remove this gamma correction, the scene seems to render appropriately, but
> this may simply be breaking one thing to cover over another and may not work
> in all circumstances (untested).
> A bug with the gamma correction of focal blur was apparently fixed in 3.1b,
> but I don't have the previous sources handy, so I can't compare them.
>
> So, what's the verdict?  Any help will be greatly appreciated, thanks.
>
> This is the test scene:
> #version 3.1;
>
> global_settings
> {
>   assumed_gamma 1.000
>   ambient_light 1.000
> }
>
> #declare blur = 0;
>
> camera
> {
>   location  < 0.000, 0.500,-1.000>
>   look_at   < 0.000, 0.000, 0.000>
>   #if(blur=1)
>     aperture 0.100
>     blur_samples 7
>     focal_point < 0.000, 0.000, 0.000>
>     confidence 0.900
>     variance 1/128
>   #end
> }
>
> light_source
> {
>   <-3.000, 2.500,-2.000>
>   color < 1.000, 1.000, 1.000>
> }
>
> sphere
> {
>   < 0.000, 0.000, 0.000>, 0.200
>   texture
>   {
>     pigment
>     {
>       colour < 1, 1, 1>
>     }
>   }
> }

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