When Thomas de Groot challenged Alain and me to write improved
metals.inc, one of my first thoughts was "Why bother? It's a lost
cause."  Alain's solution was to just replace all the ambients with 0,
but I think that's too simplistic.  That file and golds.inc were written
before POV-Ray had metallic reflection.  File golds.inc goes through an
elaborate ritual to compensate for this deficiency, while metals.inc
ignores the problem completely.  Everything about those two files
screams "OBSOLETE!"  But the challenge still gnaws at me.

One question that must be answered is should we assume that the colors
are gamma pre-encoded?  Image stock_metal_gamma-srgb.jpg assumes that
they are, and uses the srgbft keyword to decode them.  Image
stock_metal_gamma-linear.jpg assumes they are not, and just uses the
colors as-is.  Comparing them, it seems to me that the colors were not
pre-encoded, unlike those in colors.inc.

Both images use assumed_gamma 1, and the spheres use this finish:

  finish
  { ambient 0 diffuse 0
    reflection { 1 metallic }
    specular albedo 1 metallic
    roughness 1 / 3000
  }

Of course, any improvements to these files will cause old scenes to look
different.  Better, but different.

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Attachments:
Download 'stock_metal_gamma-srgb.jpg' (220 KB) Download 'stock_metal_gamma-linear.jpg' (209 KB)

Preview of image 'stock_metal_gamma-srgb.jpg'

Preview of image 'stock_metal_gamma-linear.jpg'

Op 22-2-2022 om 14:36 schreef Cousin Ricky:
> When Thomas de Groot challenged Alain and me to write improved
> metals.inc, one of my first thoughts was "Why bother? It's a lost
> cause."  Alain's solution was to just replace all the ambients with 0,
> but I think that's too simplistic.  That file and golds.inc were written
> before POV-Ray had metallic reflection.  File golds.inc goes through an
> elaborate ritual to compensate for this deficiency, while metals.inc
> ignores the problem completely.  Everything about those two files
> screams "OBSOLETE!"  But the challenge still gnaws at me.
> 
> One question that must be answered is should we assume that the colors
> are gamma pre-encoded?  Image stock_metal_gamma-srgb.jpg assumes that
> they are, and uses the srgbft keyword to decode them.  Image
> stock_metal_gamma-linear.jpg assumes they are not, and just uses the
> colors as-is.  Comparing them, it seems to me that the colors were not
> pre-encoded, unlike those in colors.inc.
> 
> Both images use assumed_gamma 1, and the spheres use this finish:
> 
>    finish
>    { ambient 0 diffuse 0
>      reflection { 1 metallic }
>      specular albedo 1 metallic
>      roughness 1 / 3000
>    }
> 
> Of course, any improvements to these files will cause old scenes to look
> different.  Better, but different.

I truly appreciate your thoughts and efforts. To address your last 
comment: I am increasingly convinced that trying at all costs to find 
solutions, at the same time preserving the aspect of old scenes, is a 
dead end. I would strongly be in favour of making those textures up to 
date, whatever the costs. For older scenes, there still are the older 
POV-Ray versions available if necessary.

-- 
Thomas

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Thomas de Groot <tho### [at] degrootorg> wrote:
> I truly appreciate your thoughts and efforts. To address your last
> comment: I am increasingly convinced that trying at all costs to find
> solutions, at the same time preserving the aspect of old scenes, is a
> dead end. I would strongly be in favour of making those textures up to
> date, whatever the costs. For older scenes, there still are the older
> POV-Ray versions available if necessary.


Agreed!

Kind regards,
Dave Blandston

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Op 22/02/2022 om 20:27 schreef Dave Blandston:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>> I truly appreciate your thoughts and efforts. To address your last
>> comment: I am increasingly convinced that trying at all costs to find
>> solutions, at the same time preserving the aspect of old scenes, is a
>> dead end. I would strongly be in favour of making those textures up to
>> date, whatever the costs. For older scenes, there still are the older
>> POV-Ray versions available if necessary.
> 
> 
> Agreed!
> 
> Kind regards,
> Dave Blandston
> 

Good. Most of the time, I avoid using the stock textures as-they-are. 
They can be a basis for use in a scene, but only after extensive changes 
at all levels. A bit frustrating I confess. Needless to say that this 
applies too to my own older scenes/textures. :-)

-- 
Thomas

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Le 2022-02-22 à 10:48, Thomas de Groot a écrit :
> Op 22-2-2022 om 14:36 schreef Cousin Ricky:
>> When Thomas de Groot challenged Alain and me to write improved
>> metals.inc, one of my first thoughts was "Why bother? It's a lost
>> cause."  Alain's solution was to just replace all the ambients with 0,
>> but I think that's too simplistic.  That file and golds.inc were written
>> before POV-Ray had metallic reflection.  File golds.inc goes through an
>> elaborate ritual to compensate for this deficiency, while metals.inc
>> ignores the problem completely.  Everything about those two files
>> screams "OBSOLETE!"  But the challenge still gnaws at me.
>>
>> One question that must be answered is should we assume that the colors
>> are gamma pre-encoded?  Image stock_metal_gamma-srgb.jpg assumes that
>> they are, and uses the srgbft keyword to decode them.  Image
>> stock_metal_gamma-linear.jpg assumes they are not, and just uses the
>> colors as-is.  Comparing them, it seems to me that the colors were not
>> pre-encoded, unlike those in colors.inc.
>>
>> Both images use assumed_gamma 1, and the spheres use this finish:
>>
>>    finish
>>    { ambient 0 diffuse 0
>>      reflection { 1 metallic }
>>      specular albedo 1 metallic
>>      roughness 1 / 3000
>>    }
>>
>> Of course, any improvements to these files will cause old scenes to look
>> different.  Better, but different.
> 
> I truly appreciate your thoughts and efforts. To address your last 
> comment: I am increasingly convinced that trying at all costs to find 
> solutions, at the same time preserving the aspect of old scenes, is a 
> dead end. I would strongly be in favour of making those textures up to 
> date, whatever the costs. For older scenes, there still are the older 
> POV-Ray versions available if necessary.
> 

Why struggle to keep old scenes to render identically when the change 
make them better ?

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Alain Martel <kua### [at] videotronca> wrote:

> >
>
> Why struggle to keep old scenes to render identically when the change
> make them better ?

Indeed ! I'm thrilled to see POV's wind of improvements and modernization.

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On 2022-02-22 11:48 (-4), Thomas de Groot wrote:
> Op 22-2-2022 om 14:36 schreef Cousin Ricky:
>>
>> Of course, any improvements to these files will cause old scenes to look
>> different.  Better, but different.
> 
> I truly appreciate your thoughts and efforts. To address your last
> comment: I am increasingly convinced that trying at all costs to find
> solutions, at the same time preserving the aspect of old scenes, is a
> dead end. I would strongly be in favour of making those textures up to
> date, whatever the costs.

Heard, loud and clear.  Plus, I went back and rendered the old metal
textures, and I don't think they will be missed.  The portfolio scenes
don't give a realistic impression of how hideous they are.

The ambients all default to zero, but for maximum flexibility, the
revised include files retain a provision for a small ambient.  I
included this provision due to my experiments last November.

All these images were rendered without radiosity, because with radiosity
in POV-Ray 3.8, the ambient issue becomes moot.  But as I wrote in the
OP, the high ambient values are not the only problem with the textures
as they have been.

If you all like these, I will post the revised include files to p.b.s-f
(and also figure out how to do branches and pull requests).

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Attachments:
Download 'metals31inc2.jpg' (90 KB) Download 'metals38inc02.jpg' (105 KB) Download 'metals38inc07.jpg' (101 KB) Download 'metals31inc5.jpg' (92 KB) Download 'metals38inc05.jpg' (125 KB) Download 'metals38inc10.jpg' (121 KB)

Preview of image 'metals31inc2.jpg'

Preview of image 'metals38inc02.jpg'

Preview of image 'metals38inc07.jpg'

Preview of image 'metals31inc5.jpg'

Preview of image 'metals38inc05.jpg'

Preview of image 'metals38inc10.jpg'

Op 24/02/2022 om 00:31 schreef Cousin Ricky:
> 
> If you all like these, I will post the revised include files to p.b.s-f
> (and also figure out how to do branches and pull requests).

Perfect!

I vote for the addition of a small ambient.

-- 
Thomas

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Il 24/02/2022 00:31, Cousin Ricky ha scritto:

 > If you all like these, I will post the revised include files to p.b.s-f
 > (and also figure out how to do branches and pull requests).

Yes, please, the examples are really nice.
Thank you,
    Paolo

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On 2022-02-22 09:36 (-4), Cousin Ricky wrote:
> 
> One question that must be answered is should we assume that the colors
> are gamma pre-encoded?  Image stock_metal_gamma-srgb.jpg assumes that
> they are, and uses the srgbft keyword to decode them.  Image
> stock_metal_gamma-linear.jpg assumes they are not, and just uses the
> colors as-is.  Comparing them, it seems to me that the colors were not
> pre-encoded, unlike those in colors.inc.

I discovered that the demo scenes from POV-Ray 3.0 explicitly set
assumed_gamma to 2.2, suggesting that the pigment colors were gamma
pre-encoded.  However, as the first OP image shows, this results in
metals that are too dark when used with a realistic finish.  It appears
that the old finishes exaggerated the luminances of the colors while
reducing their saturations, so it seems best to leave the colors as-is,
as if they were not pre-encoded.

Not gamma-decoding the colors does result in hue drift, but I think the
drift is in a better direction.

The attached images show the old finishes without and with radiosity.
Since they were rendered with POV-Ray 3.7, the ambients were
automatically suppressed for the radiosity renders.  The radiosity image
shows that the ambients were not the only problem with the old finishes;
the reflection { metallic } introduced in POV-Ray 3.5 really makes a
difference.

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Attachments:
Download 'stock_metalc_gamma-srgb-a.jpg' (211 KB) Download 'stock_metalc_gamma-srgb-r.jpg' (211 KB)

Preview of image 'stock_metalc_gamma-srgb-a.jpg'

Preview of image 'stock_metalc_gamma-srgb-r.jpg'