POV-Ray : Newsgroups : povray.beta-test : Difference between 3.6 and 3.7 in image Server Time: 15 Sep 2019 22:15:22 GMT
  Difference between 3.6 and 3.7 in image (Message 1 to 7 of 7)  
From: jkroby
Subject: Difference between 3.6 and 3.7 in image
Date: 2 Nov 2011 16:35:01
Message: <web.4eb1708933665a8538b76eca0@news.povray.org>
Hi, is my first post.
I downloaded povray-3.7.0.RC3 subsurface features to try to use in MH and doing
some testing I noticed an abysmal difference, the image was much clearer, even
if I disable all, the configuration files are the same for povray 3.6 and 3.7.
I made a fool of bullshit?
Using povray for over 10 years although in a discontinuous manner.
But all use the same files and I can not explain all of this difference, I made
&#8203;&#8203;a little 'of changes to the original file but in the MH 2 images
using all the same.

Images:
povray 3.7
http://www.p3r.info/povray/new.png
povray 3.6
http://www.p3r.info/povray/ref.png

Some ideas?
Roberto


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From: Warp
Subject: Re: Difference between 3.6 and 3.7 in image
Date: 2 Nov 2011 17:03:36
Message: <4eb177e8@news.povray.org>
jkroby <jkr### [at] p3rinfo> wrote:
> I downloaded povray-3.7.0.RC3 subsurface features to try to use in MH and doing
> some testing I noticed an abysmal difference, the image was much clearer, even
> if I disable all, the configuration files are the same for povray 3.6 and 3.7.

  Are you using "#version 3.7"? If yes, then you need to either:

1) define your colors using 'srgb' instead of 'rgb' (and use 'assumed_gamma'
   with image maps),

2) use "assumed_gamma 2.2" in the global_settings block if you want to get
   the same gamma behavior as with POV-Ray 3.6, or

3) remove the #version directive (or use "#version 3.6"), which achieves
   the same as option 2 above.

  It is generally recommended to use option 1, but when transferring a scene
from 3.6 to 3.7 it may be more convenient to use one of the other two options.
(Also things like color maps cannot yet be replicated in 3.7 using the
default assumed_gamma 1.0, so that might be another situation where you
may need to compromise and use assumed_gamma 2.2.)

-- 
                                                          - Warp


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From: clipka
Subject: Re: Difference between 3.6 and 3.7 in image
Date: 3 Nov 2011 08:55:38
Message: <4eb2570a@news.povray.org>
Am 02.11.2011 17:32, schrieb jkroby:
> Hi, is my first post.
> I downloaded povray-3.7.0.RC3 subsurface features to try to use in MH and doing
> some testing I noticed an abysmal difference, the image was much clearer, even
> if I disable all, the configuration files are the same for povray 3.6 and 3.7.
> [...]
>
> Images:
> povray 3.7
> http://www.p3r.info/povray/new.png
> povray 3.6
> http://www.p3r.info/povray/ref.png
>
> Some ideas?

Yes: "Gamma" is the buzzword.

See 
http://wiki.povray.org/content/Documentation:Tutorial_Section_3.3#Gamma_Handling 
for more information.


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From: Warp
Subject: Re: Difference between 3.6 and 3.7 in image
Date: 3 Nov 2011 09:13:20
Message: <4eb25b2f@news.povray.org>
clipka <ano### [at] anonymousorg> wrote:
> http://wiki.povray.org/content/Documentation:Tutorial_Section_3.3#Gamma_Handling 

  Btw, I think that the description of the first image is a bit lacking.
With which I mean it's a bit ambiguous.

  When it says "but the pigment is a mere 21.8% as bright as the rightmost
one. The true 50% brightness sphere sits right behind it" it's confusing
without a clarifying explanation of what it's talking about.

  It's the old problem with absolute brightness vs. perceived brightness
(iow. what the human eye sees as the brithness being). When that text uses
the numbers "21.8%" and "50%" it's talking about absolute brightness, iow the
amount of energy emitted by those pixels. However, most people don't realize
this and only think in terms of perceived brightness, iow. what they see.
In terms of the latter, the front row is (almost) linear while the second
row isn't.

  The problem with that is that people will tend to disagree with the
description. "What do you mean the sphere in the middle of the second row
is 50% bright? It clearly isn't. It's much brighter than that." Such a
disagreement, spawning from the ambiguous description, easily leads to
rejecting the whole concept of the new gamma handling.

  A technical description between absolute brightness and perceived
brightness, one which is easy to understand, and why this distinction is
important in randering, may be hard to write, but I think it's necessary
in order to avoid confusion.

-- 
                                                          - Warp


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From: jkroby
Subject: Re: Difference between 3.6 and 3.7 in image
Date: 3 Nov 2011 13:00:01
Message: <web.4eb28fe473a6682438b76eca0@news.povray.org>
Many thanks!
Ok!


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From: Jim Holsenback
Subject: Re: Difference between 3.6 and 3.7 in image
Date: 3 Nov 2011 14:33:10
Message: <4eb2a626$1@news.povray.org>
On 11/03/2011 04:55 AM, clipka wrote:
> Am 02.11.2011 17:32, schrieb jkroby:
>> Hi, is my first post.
>> I downloaded povray-3.7.0.RC3 subsurface features to try to use in MH
>> and doing
>> some testing I noticed an abysmal difference, the image was much
>> clearer, even
>> if I disable all, the configuration files are the same for povray 3.6
>> and 3.7.
>> [...]
>>
>> Images:
>> povray 3.7
>> http://www.p3r.info/povray/new.png
>> povray 3.6
>> http://www.p3r.info/povray/ref.png
>>
>> Some ideas?
>
> Yes: "Gamma" is the buzzword.
>
> See
> http://wiki.povray.org/content/Documentation:Tutorial_Section_3.3#Gamma_Handling
> for more information.

indeed! ... another GREAT place to start looking when something acts 
differently (3.6 -vs- 3.7) is:
http://wiki.povray.org/content/Documentation:Tutorial_Section_1#Changes_and_New_Features_Summary

and bonus tip of the day ... the distribution docs have a link that will 
land you in the same place ... locally that is ;-)


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From: Jim Holsenback
Subject: Re: Difference between 3.6 and 3.7 in image
Date: 4 Nov 2011 17:59:25
Message: <4eb427fd$1@news.povray.org>
On 11/03/2011 10:33 AM, Jim Holsenback wrote:
> and bonus tip of the day ... the distribution docs have a link that will
> land you in the same place ... locally that is ;-)

Well geez ... I guess I should qualify that a bit more and add that the 
link to the new features section is mentioned in the opening page 
narrative ... doh!


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