POV-Ray : Newsgroups : povray.beta-test : Gamma Handling in Beta 19 Server Time: 26 Sep 2020 08:24:15 GMT
  Gamma Handling in Beta 19 (Message 1 to 4 of 4)  
From: Ben Chambers
Subject: Gamma Handling in Beta 19
Date: 31 Jan 2007 22:57:49
Message: <45c11eed$1@news.povray.org>
After reading Thorsten's reply in P.G., I'm putting this here.

Images output by POV-Ray 3.7 Beta display too brightly in *some* programs.

The Gimp handles them fine.

Firefox displays them too brightly.

According to the Mozilla team, the gamma is stored wrong in the file. 
It is stored as 2.2 when it should be 1.0/2.2.

I have tested force replacing the gamma with PNGCrush, and replacing it 
with .4545 (1.0/2.2) results in an image that displays correctly in all 
programs.

...Chambers


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From: Warp
Subject: Re: Gamma Handling in Beta 19
Date: 31 Jan 2007 23:05:49
Message: <45c120cd@news.povray.org>
Ben Chambers <ben### [at] pacificwebguycom> wrote:
> I have tested force replacing the gamma with PNGCrush, and replacing it 
> with .4545 (1.0/2.2) results in an image that displays correctly in all 
> programs.

  I'm puzzled about why the gimp shows the image correctly regardless
of whether it has a gamma of 2.2 or 0.4545

-- 
                                                          - Warp


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From: Thorsten Froehlich
Subject: Re: Gamma Handling in Beta 19
Date: 31 Jan 2007 23:35:36
Message: <45c127c8@news.povray.org>
Warp wrote:
> Ben Chambers <ben### [at] pacificwebguycom> wrote:
>> I have tested force replacing the gamma with PNGCrush, and replacing it 
>> with .4545 (1.0/2.2) results in an image that displays correctly in all 
>> programs.
> 
>   I'm puzzled about why the gimp shows the image correctly regardless
> of whether it has a gamma of 2.2 or 0.4545

The libpng spec isn't completely conclusive as to what the right value
should be ... so maybe they support both (that is if gamma is below 1 or
something)

	Thorsten


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From: Ive
Subject: Re: Gamma Handling in Beta 19
Date: 1 Feb 2007 00:58:17
Message: <45c13b29@news.povray.org>
"Thorsten Froehlich" <tho### [at] trfde> schrieb im Newsbeitrag 
news:45c127c8@news.povray.org...
> Warp wrote:
>> Ben Chambers <ben### [at] pacificwebguycom> wrote:
>>> I have tested force replacing the gamma with PNGCrush, and replacing it
>>> with .4545 (1.0/2.2) results in an image that displays correctly in all
>>> programs.
>>
>>   I'm puzzled about why the gimp shows the image correctly regardless
>> of whether it has a gamma of 2.2 or 0.4545
>
> The libpng spec isn't completely conclusive as to what the right value
> should be ... so maybe they support both (that is if gamma is below 1 or
> something)
>
> Thorsten

Nope. The Gimp simply assumes that every png image is 2.2 gamma
corrected and is just lucky in this special case.

-Ive


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