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I am working on a POV-Ray project which involves loading an external image
and re-displaying it with no color adjustment. I recently discovered that
"ambient 1" with no light_sources is not enough; the picture comes out
brighter than the original. I traced the problem to the picture below. The
top band is POV-Ray's rendering of a smooth gradient black to white at
ambient 1 with no light_sources. The bottom band is an unmodified gradient
black to white made by Fireworks. I hold in doubt neither gradient, and I
think the problem lies in how the object color is transformed into a final
pixel color. What is going on, and how can I disable or counter this
change?
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Attachments:
Download 'bob.png' (2 KB)
Preview of image 'bob.png'
![bob.png](/povray.binaries.images/attachment/%3Cweb.457ddbc7f15bc39baf9a4b290%40news.povray.org%3E/bob.png?ttop=443866&toff=4100&preview=1)
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Di Gama wrote:
> I am working on a POV-Ray project which involves loading an external image
> and re-displaying it with no color adjustment. I recently discovered that
> "ambient 1" with no light_sources is not enough; the picture comes out
> brighter than the original. I traced the problem to the picture below. The
> top band is POV-Ray's rendering of a smooth gradient black to white at
> ambient 1 with no light_sources. The bottom band is an unmodified gradient
> black to white made by Fireworks. I hold in doubt neither gradient, and I
> think the problem lies in how the object color is transformed into a final
> pixel color. What is going on, and how can I disable or counter this
> change?
Try looking up "assumed gamma" and "display gamma".
Basically, POV-Ray "ships" with display gamma set to 2.2 (on Windows)
and you should set assumed_gamma in global_settings to 2.2 as well to
make no gamma-changes on loaded pictures. This kinda doesn't work with
PNG, depending if the gamma is encoded within it or not...
All in all, it's a slightly complicated matter, but experiment and
you'll learn. :-)
Regards,
Tim
--
aka "Tim Nikias"
Homepage: <http://www.nolights.de>
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I'm not 100% sure, but I suspect the assumed_gamma setting of povray.
global_settings { assumed_gamma 1.0 }
does that change anything ?
http://www.povray.org/documentation/view/3.6.1/260/
jaap.
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try with
global_settings {
assumed_gamma 2.2
}
in the top of ur code
greeting for all is my first post in the list
"Di Gama" <di.### [at] gmail com> wrote:
> I am working on a POV-Ray project which involves loading an external image
> and re-displaying it with no color adjustment. I recently discovered that
> "ambient 1" with no light_sources is not enough; the picture comes out
> brighter than the original. I traced the problem to the picture below. The
> top band is POV-Ray's rendering of a smooth gradient black to white at
> ambient 1 with no light_sources. The bottom band is an unmodified gradient
> black to white made by Fireworks. I hold in doubt neither gradient, and I
> think the problem lies in how the object color is transformed into a final
> pixel color. What is going on, and how can I disable or counter this
> change?
Post a reply to this message
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Here's what I did to import my photos...
global_settings {
// assumed_gamma 1.0
}
light_source {
0*x
color rgb <1,1,1>*1.5
parallel
point_at <0, 0, 1>
translate <0, 0, -1>
}
I did nothing else with lighting... not even adjust the "diffuse". I played
with "assumed_gamma" but decided not to use it. A few tests showed that the
rendered image looked exactly like the photo.
----- Original Message -----
From: "Di Gama" <di.### [at] gmail com>
Newsgroups: povray.binaries.images
Sent: Monday, December 11, 2006 4:29 PM
Subject: brightness adjustment
>I am working on a POV-Ray project which involves loading an external image
> and re-displaying it with no color adjustment. I recently discovered that
> "ambient 1" with no light_sources is not enough; the picture comes out
> brighter than the original. I traced the problem to the picture below. The
> top band is POV-Ray's rendering of a smooth gradient black to white at
> ambient 1 with no light_sources. The bottom band is an unmodified gradient
> black to white made by Fireworks. I hold in doubt neither gradient, and I
> think the problem lies in how the object color is transformed into a final
> pixel color. What is going on, and how can I disable or counter this
> change?
>
Post a reply to this message
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"Di Gama" <di.### [at] gmail com> wrote in message
news:web.457ddbc7f15bc39baf9a4b290@news.povray.org...
>I am working on a POV-Ray project which involves loading an external image
> and re-displaying it with no color adjustment. I recently discovered that
> "ambient 1" with no light_sources is not enough; the picture comes out
> brighter than the original. I traced the problem to the picture below. The
> top band is POV-Ray's rendering of a smooth gradient black to white at
> ambient 1 with no light_sources. The bottom band is an unmodified gradient
> black to white made by Fireworks. I hold in doubt neither gradient, and I
> think the problem lies in how the object color is transformed into a final
> pixel color. What is going on, and how can I disable or counter this
> change?
I suppose you're using PNG? PNG contains gamma-correction, so if the
gamma-settings in the PNG are different from what POV-Ray uses, POV-Ray
"automatically" corrects it.
So you should make sure you're using the exact same settings, or that you don't
use PNG
cu!
--
#macro G(b,e)b+(e-b)*C/50#end#macro _(b,e,k,l)#local C=0;#while(C<50)
sphere{G(b,e)+3*z.1pigment{rgb G(k,l)}finish{ambient 1}}#local C=C+1;
#end#end _(y-x,y,x,x+y)_(y,-x-y,x+y,y)_(-x-y,-y,y,y+z)_(-y,y,y+z,x+y)
_(0x+y.5+y/2x)_(0x-y.5+y/2x) // ZK http://www.povplace.com
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"Di Gama" <di.### [at] gmail com> wrote:
> I am working on a POV-Ray project which involves loading an external image
> and re-displaying it with no color adjustment. I recently discovered that
> "ambient 1" with no light_sources is not enough; the picture comes out
> brighter than the original. I traced the problem to the picture below. The
> top band is POV-Ray's rendering of a smooth gradient black to white at
> ambient 1 with no light_sources. The bottom band is an unmodified gradient
> black to white made by Fireworks. I hold in doubt neither gradient, and I
> think the problem lies in how the object color is transformed into a final
> pixel color. What is going on, and how can I disable or counter this
> change?
I tried setting assumed_gamma to everything under the sun, but I see
absolutely no change in the image. The help text on gamma was very
confusing. I am not using any special gamma additions, and I am viewing the
original and re-rendered pictures on the same monitor, so display gamma is
irrelevant. I am rendering to a BMP on a Windows. Here is the source for
the gradient picture:
global_settings { assumed_gamma 1 }
camera {
direction .5*z
right x
up y
}
box {
<0,-1,1>,<1,1,2>
pigment {gradient x}
finish {ambient 1}
scale 1+x
translate -x
}
This source is not shortened at all.
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