For your judgment.

A comparison of different versions of Dakota Red (aka Mahogany) granites:

-The first row are the original textures, rendered with Ive's code;
-the second row are my "original"(*) textures with 'rgb' replaced simply 
by 'srgb';
- the third row are my "original"(*) textures with 'rgb' converted to 
'srgb';

At the right, a few Real World Dakota Red photographs from the net.

(*) I noticed that the colour_maps from the original code by Daniel 
Mecklenburg Jr in 1996 are of the form < 0.09, 0.03, 0.06 >, while my 
own originals are of the form < 0.086, 0.027, 0.059 >. So it seems that 
in between 1996 and an unknown (earlier? later?) date, another version 
was posted in the POV-Ray universe...

-- 
Thomas

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Thomas de Groot <tho### [at] degrootorg> wrote:
> For your judgment.

Well, it looks like the simple procedural noise that's used for the basis
pattern is much too round and smooth.  The grains in the real granite are much
sharper and [rect]angular.

It's not clear to me exactly how to achieve that,
but I think that there should be a move away from a very smooth gradient noise,
toward something that will give a more crystalline, granular look, perhaps with
an asymmetric step to it - to make those quartz outlines in the one sample.

Could you please try:

#declare Granite = pigment {
     cells turbulence 0.425 //(0.325 is too low)
     color_map {Whatever you're using}
}

to see what I mean?
I'm interested in seeing a similar render to what you just posted, perhaps with
whatever improvements you might discover.



https://wiki.povray.org/content/HowTo:Turn_a_continuous_function_into_a_stepped_function
https://stackoverflow.com/questions/42823308/make-perlin-noise-with-sharp-edges

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Op 25/04/2021 om 21:49 schreef Bald Eagle:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>> For your judgment.
> 
> Well, it looks like the simple procedural noise that's used for the basis
> pattern is much too round and smooth.  The grains in the real granite are much
> sharper and [rect]angular.
> 
Yes, that is one of my worries.

> It's not clear to me exactly how to achieve that,
> but I think that there should be a move away from a very smooth gradient noise,
> toward something that will give a more crystalline, granular look, perhaps with
> an asymmetric step to it - to make those quartz outlines in the one sample.
> 
The granite pattern is (almost) correct (without the turbulence).

> Could you please try:
> 
> #declare Granite = pigment {
>       cells turbulence 0.425 //(0.325 is too low)
>       color_map {Whatever you're using}
> }
> 
> to see what I mean?
> I'm interested in seeing a similar render to what you just posted, perhaps with
> whatever improvements you might discover.
> 
Sure.

>
https://wiki.povray.org/content/HowTo:Turn_a_continuous_function_into_a_stepped_function
> https://stackoverflow.com/questions/42823308/make-perlin-noise-with-sharp-edges
> 

HOWEVER!
I should have made my first intention with this image more clear as the 
grain form and distribution are the next steps.

It is the /texture colour/ which prompted my post: It appears - and not 
only with this particular texture - that the original ones, rendered 
with Ive's code (deprecated gamma 1.8, etc) are similar to my own 
version of the set when using /srgb/ instead of /rgb/ in the 
colour_maps! This is interesting because it means that only a minimum of 
conversion is needed to get identical results to the originals. The case 
of the frosted granite is different as the first author used a different 
colour_map for that one in the first place. I do not know why. To be 
investigated.

It also explains more comprehensively the original name: Mahogany. The 
colour is similar to mahogany wood. Afaiac, I believe I should follow 
that path in the first place and maybe disregard my own lighter version 
(or not). Not sure yet. What do you think? Independently of your 
comments above which are of a different order of course.

-- 
Thomas

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Op 25/04/2021 om 21:49 schreef Bald Eagle:
> Could you please try:
> 
> #declare Granite = pigment {
>       cells turbulence 0.425 //(0.325 is too low)
>       color_map {Whatever you're using}
> }
> 
> to see what I mean?
> I'm interested in seeing a similar render to what you just posted, perhaps with
> whatever improvements you might discover.
> 

Quick-and-Dirty.

Yes, this is promising indeed! Good thinking!

-- 
Thomas

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Op 26/04/2021 om 08:55 schreef Thomas de Groot:
> Quick-and-Dirty.
> 
> Yes, this is promising indeed! Good thinking!
> 

...and with an appropriate pigment_pattern.

Later today I shall study those two sites and see if I can use the info.

-- 
Thomas

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Thomas de Groot <tho### [at] degrootorg> wrote:

Thanks for making the render.  Looks better than my sphere - which looks like a
cheap hard-rubber bowling ball, or the foam they use in sofa cushions.  :D

Needs 0.2-0.3 more turbulence. ;)

> The granite pattern is (almost) correct (without the turbulence).

I don't know what you mean.

> It also explains more comprehensively the original name: Mahogany. The
> colour is similar to mahogany wood. Afaiac, I believe I should follow
> that path in the first place and maybe disregard my own lighter version
> (or not). Not sure yet. What do you think?

Well, there are myriad samples available at stonecontact-dot-com, all of which
fall under the blanket/umbrella trade name of Dakota Mahogany and which have
widely differing "color maps".

I think we need to alternate in our approach to this, and on the one hand try to
formulaicly mimic the underlying patterns and sub-patterns, but on the other
hand not forget that we can do some good ole' raytracing sleight-of-hand and do
everything we can to fool the eye and mind into believing that they see
something that is not there.

One thing I thought of was to take a/some granite photos and run some
edge-finding filters on them to see what pops out.

I'm curious about the rgb color mapping - the individual values - but also,
given an individual grain region, what is the rgb variation across it?  How much
secondary or tertiary pigment is patterned into the grain?

Is there a way to estimate the grain sizes from the photos?  Or maybe there is
statistical data in the literature?

I ran across a neat conformal mapping image with circle packing that looked like
a good mathematical way to get discrete regions with good grain-size variation.

AFAIK, we're using straight Perlin noise right now for granite.   Doing floor()
on each of the axes produces the cells {} pattern.  I'm thinking if we could
split the difference.... maybe with the step trick and/or select ()

Also need to keep in mind that the base pattern might just be a guide, and the
final "look" is going to likely be a result of layering textures/materials.
Hard to visualize.

And lastly, there were the brick pattern and random hexagon color threads that
employed methods we might be able to use here.

http://news.povray.org/povray.general/thread/%3C5ae17c9c%40news.povray.org%3E/?mtop=422221&moff=10

http://news.povray.org/povray.binaries.images/thread/%3Cweb.5ad633941828641ca47873e10%40news.povray.org%3E/?mtop=422589

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Thomas de Groot <tho### [at] degrootorg> wrote:
> Op 26/04/2021 om 08:55 schreef Thomas de Groot:
> > Quick-and-Dirty.
> >
> > Yes, this is promising indeed! Good thinking!
> >
>
> ...and with an appropriate pigment_pattern.
>
> Later today I shall study those two sites and see if I can use the info.
>
> --
> Thomas

Exciting ! Now the tint looks spot on and better than the original.
About pattern, however, the fact that both Ive's and your own "quick and dirty"
versions feel more pleasing seems to confirm that the flakes scale may be
slightly too small, even for realistic measurements. Though I do understand that
Ive's scale is not acceptable to the rock specialist's expertise. Maybe a
compromise could be found if the noise depth is not yet too low and could be
reduced one level so as not to generate too small of a minimal cell?

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Op 26-4-2021 om 13:11 schreef Mr:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>> Op 26/04/2021 om 08:55 schreef Thomas de Groot:
>>> Quick-and-Dirty.
>>>
>>> Yes, this is promising indeed! Good thinking!
>>>
>>
>> ...and with an appropriate pigment_pattern.
>>
>> Later today I shall study those two sites and see if I can use the info.
>>
>> --
>> Thomas
> 
> Exciting ! Now the tint looks spot on and better than the original.
> About pattern, however, the fact that both Ive's and your own "quick and dirty"
> versions feel more pleasing seems to confirm that the flakes scale may be
> slightly too small, even for realistic measurements. Though I do understand that
> Ive's scale is not acceptable to the rock specialist's expertise. Maybe a
> compromise could be found if the noise depth is not yet too low and could be
> reduced one level so as not to generate too small of a minimal cell?
> 
Finding the correct size/distribution of individual minerals is going to 
be a careful and slow process. Each pattern has its own range of scales; 
if I concentrate on /cells/ as in the latest image, the smallest should 
be a bit larger and the largest a bit smaller. ;-)

However, even in a RW granite, the very smallest minerals can only be 
distinguished through a microscope, forming  the basic matrix of the 
rock. Largest minerals can be really large, forming so-called 
/phenocrysts/. For those interested: 
https://en.wikipedia.org/wiki/Phenocryst .

-- 
Thomas

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This is a version of the frosted granite, with quartz veins, but also 
with ligh-coloured minerals in the matrix.

-- 
Thomas

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Op 26/04/2021 om 12:47 schreef Bald Eagle:
> Thomas de Groot <tho### [at] degrootorg> wrote:
> 
> Thanks for making the render.  Looks better than my sphere - which looks like a
> cheap hard-rubber bowling ball, or the foam they use in sofa cushions.  :D
> 
> Needs 0.2-0.3 more turbulence. ;)
> 
>> The granite pattern is (almost) correct (without the turbulence).
> 
> I don't know what you mean.
> 
The original granite code contains turbulence. That is one of the 
reasons the original granite looks like a 'flow' pattern. The first 
thing I did was to comment out the turbulence; the granite became more 
'crispy' and closer to the real thing.

>> It also explains more comprehensively the original name: Mahogany. The
>> colour is similar to mahogany wood. Afaiac, I believe I should follow
>> that path in the first place and maybe disregard my own lighter version
>> (or not). Not sure yet. What do you think?
> 
> Well, there are myriad samples available at stonecontact-dot-com, all of which
> fall under the blanket/umbrella trade name of Dakota Mahogany and which have
> widely differing "color maps".
> 
I know. One of the problems is probably also that we do not know how 
much photoshopping has been applied to those photographs. However, I 
strongly believe that there is a link between the trade name and the 
deep hue of the mahogany wood. It would certainly help the sell.

> I think we need to alternate in our approach to this, and on the one hand try to
> formulaicly mimic the underlying patterns and sub-patterns, but on the other
> hand not forget that we can do some good ole' raytracing sleight-of-hand and do
> everything we can to fool the eye and mind into believing that they see
> something that is not there.
> 
Oh yes.

> One thing I thought of was to take a/some granite photos and run some
> edge-finding filters on them to see what pops out.
> 
> I'm curious about the rgb color mapping - the individual values - but also,
> given an individual grain region, what is the rgb variation across it?  How much
> secondary or tertiary pigment is patterned into the grain?
> 
That is a tedious exercise ;-) I did it years ago to get correct colour 
values for Mediterranean-style roof tiles (for which I used the cells 
pattern, btw). Can be done of course; I shall put it on my 
ToDo/ToExplore list.

> Is there a way to estimate the grain sizes from the photos?  Or maybe there is
> statistical data in the literature?
> 
That is more difficult. Literature tells me that grain sizes range from 
microscopic to about 10-15mm in most cases and within the same granite, 
with sometimes larger minerals (phenocrysts) in the more porphyric 
varieties. See my answer to Mr.

> I ran across a neat conformal mapping image with circle packing that looked like
> a good mathematical way to get discrete regions with good grain-size variation.
> 
> AFAIK, we're using straight Perlin noise right now for granite.   Doing floor()
> on each of the axes produces the cells {} pattern.  I'm thinking if we could
> split the difference.... maybe with the step trick and/or select ()
> 
> Also need to keep in mind that the base pattern might just be a guide, and the
> final "look" is going to likely be a result of layering textures/materials.
> Hard to visualize.
> 
> And lastly, there were the brick pattern and random hexagon color threads that
> employed methods we might be able to use here.
> 
All the above: yes; might need additional investigation. Concerning the 
hexagon pattern: many if not most of the granite minerals are hexagonal. 
That would mean it would be more appropriate for granites. However, I am 
afraid it would look 'circular' in practice.

>
http://news.povray.org/povray.general/thread/%3C5ae17c9c%40news.povray.org%3E/?mtop=422221&moff=10
> 
>
http://news.povray.org/povray.binaries.images/thread/%3Cweb.5ad633941828641ca47873e10%40news.povray.org%3E/?mtop=422589
> 

-- 
Thomas

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