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>
    }
  }
}

Post a reply to this message

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>
>     }
>   }
> }

Post a reply to this message

Andrea Ryan <ary### [at] global2000net> wrote in message
news:380A7F33.46F5F932@global2000.net...
> 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

While I appreciate your suggestion, it is more of a work-around than a
bug-fix.  I choose to use a gamma of 1.0 in accordance with the POV-Ray
documentation, but I really should be able to use whatever gamma I want and
not have this discrepancy.

Post a reply to this message

Oh... The docs say that assumed_gamma 1.0 will model the way light looks in the
real world.
Brendan Ryan

Edward Coffey wrote:

> Andrea Ryan <ary### [at] global2000net> wrote in message
> news:380A7F33.46F5F932@global2000.net...
> > 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
>
> While I appreciate your suggestion, it is more of a work-around than a
> bug-fix.  I choose to use a gamma of 1.0 in accordance with the POV-Ray
> documentation, but I really should be able to use whatever gamma I want and
> not have this discrepancy.

Post a reply to this message

I had a Scarlet plane with reflection 0.25 and a blue sky_sphere with white clouds.
With assumed_gamma 1.0, the plane turns purple (red+blue=purple). So... the bug
should be fixed since assumed_gamma 1.0 looks more real.
Brendan Ryan

Andrea Ryan wrote:

> Oh... The docs say that assumed_gamma 1.0 will model the way light looks in the
> real world.
> Brendan Ryan
>
> Edward Coffey wrote:
>
> > Andrea Ryan <ary### [at] global2000net> wrote in message
> > news:380A7F33.46F5F932@global2000.net...
> > > 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
> >
> > While I appreciate your suggestion, it is more of a work-around than a
> > bug-fix.  I choose to use a gamma of 1.0 in accordance with the POV-Ray
> > documentation, but I really should be able to use whatever gamma I want and
> > not have this discrepancy.

Post a reply to this message

On Mon, 18 Oct 1999 07:49:45 +1000, "Edward Coffey"
<e.c### [at] ugradunimelbeduau> wrote:

>The scene below renders much brighter when you turn focal blur on
>[..]

  Edward, thanks for reporting this earlier. Nathan Kopp has verified and
found a fix for this gamma correction bug in the official POV-Ray source. It
is now posted on povray.bugreports. It will be fixed in the next release of
POV-Ray (and UVPov), release date yet unknown.

-- 
Alan - ako### [at] povrayorg - a k o n g <at> p o v r a y <dot> o r g
http://www.povray.org - Home of the Persistence of Vision Ray Tracer

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