Opinions sought.

http://www21.brinkster.com/jrcsurvey/Temp/index.html


The link is to  some test renders permutating different
combinations for background, specular, and roughness.

Constants:
pigment { rgb 0 }
diffuse 1
reflection { .075 .15 fresnel metallic 0 }

Which looks best?

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Jim Charter wrote:
> Which looks best?
23

Cheers!
Rick Measham

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I took a look, then came back later and took another look, and I would have 
to agree with Rick.  #23 looks best to me, especially if you're looking for 
shiny leather.

> pigment { rgb 0 }

I've found that I get better results when I use a very small RGB value, 
rather than 0.  You might want to experiment with that as well.  RGB 0 can 
look very strange when placed with other objects, in my experience.  Perhaps 
something like "rgb <0.001, 0.001, 0.001>" or for a slightly bluish tint 
"rgb <0.001, 0.001, 0.003>"

> diffuse 1
> reflection { .075 .15 fresnel metallic 0 }

Jaime recently mentioned "diffuse + reflection = 1".  From looking at some 
of his code, it appears that he always uses the first reflection component, 
which would give you a diffuse of 0.925.  Not a huge difference, but it 
might make a subtle difference.

Would the bottom (base?) of the shoe have a different specular component?

Just some thoughts.

-- 
Jeremy
www.beantoad.com

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Jeremy M. Praay wrote:
> I took a look, then came back later and took another look, and I would have 
> to agree with Rick.  #23 looks best to me, especially if you're looking for 
> shiny leather.
> 
> 
>>pigment { rgb 0 }
> 
> 
> I've found that I get better results when I use a very small RGB value, 
> rather than 0.  You might want to experiment with that as well.  RGB 0 can 
> look very strange when placed with other objects, in my experience.  Perhaps 
> something like "rgb <0.001, 0.001, 0.001>" or for a slightly bluish tint 
> "rgb <0.001, 0.001, 0.003>"
> 
> 
>>diffuse 1
>>reflection { .075 .15 fresnel metallic 0 }
> 
> 
> Jaime recently mentioned "diffuse + reflection = 1".  From looking at some 
> of his code, it appears that he always uses the first reflection component, 
> which would give you a diffuse of 0.925.  Not a huge difference, but it 
> might make a subtle difference.
> 
> Would the bottom (base?) of the shoe have a different specular component?
> 
> Just some thoughts.
> 
I think the diffuse component is irrelevent for rgb 0.  I think it is 
basically the product of the two values, rgb and diffuse, and the angle 
of the lightray, that are used to calculate shadow.  So if you go rgb 0 
you loose all capacity to get non-lighted shadows and instead have to 
rely on specular and/or reflection to mold the surface.  So, as you say, 
adding a little color gives "diffuse" something to work with.  The 
trouble is that just about the time that adding color starts to make a 
difference, it starts to look like grey, not black, material.

Yes I remember Jaime's suggestion too, though I thought he was talking 
about specular.  I also remember that a long time ago there were often 
threads discussing such formulas. Alas, am I now just catching up? Well 
not quite. For a long long time I typically adjusted 
diffuse/specular/reflection as some sort of loosely conceived division 
up of a unit whole.  Then it came as something of a revelation to me 
when I freed myself from that discipline.  Now, while Jaime's statement 
comes as a sobering remainder to keep it sane, I am still not convinced 
that a formulaic relationship between these elements always makes sense.

I was introducing my daughter to raytracing just the other night.  We 
were giving a sphere, with no finish specified, different colors just to 
demonstrate how the color vector worked.  I was trying to get her to 
guess how to get yellow by introducing the concept that yellow is really 
not-blue.  So first I had to demonstrate that white is <1,1,1>. We did 
the render.  "It doesn't look white, it looks grey", was her immediate 
reaction. :(

With a low rgb, radiosity also is neutralized.  So the only way to get 
any tones into the shadows is reflection. But even the slightest amount 
of reflection gives a hard-shiny look.

About the bottom of the shoe. ("Bottom" is the correct term.) Yes, if it 
was made of leather it would show wear and have tan patches.  If not, 
then it would be some homogenous material other than leather and 
therefore show different surface characteristics.  It is an important 
question because it may be true that the solution to the problem has to 
do with providing massive amounts of minute surface detail.  After all, 
shiny, homogenous, black patent leather is favored by some precisely for 
its "dark liquid", form-denying properties.

So the hunt goes on.  But I was interested to peoples reactions to gross 
adjustments of these factors across the scene in general.

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"Jim Charter" <jrc### [at] msncom> wrote in message 
news:42569e69@news.povray.org...
> I think the diffuse component is irrelevent for rgb 0.  I think it is 
> basically the product of the two values, rgb and diffuse, and the angle of 
> the lightray, that are used to calculate shadow.  So if you go rgb 0 you 
> loose all capacity to get non-lighted shadows and instead have to rely on 
> specular and/or reflection to mold the surface.  So, as you say, adding a 
> little color gives "diffuse" something to work with.  The trouble is that 
> just about the time that adding color starts to make a difference, it 
> starts to look like grey, not black, material.

Very true.  Though in some cases, I've had rgb 0 objects show up like black 
holes in the middle of a picture, and giving it a very small value still 
makes it appear black, without making it look like there's black hole in the 
picture.  But if it looks ok in relation to other objects, no reason to 
change it.

>
> Yes I remember Jaime's suggestion too, though I thought he was talking 
> about specular.  I also remember that a long time ago there were often 
> threads discussing such formulas. Alas, am I now just catching up? Well 
> not quite. For a long long time I typically adjusted 
> diffuse/specular/reflection as some sort of loosely conceived division up 
> of a unit whole.  Then it came as something of a revelation to me when I 
> freed myself from that discipline.  Now, while Jaime's statement comes as 
> a sobering remainder to keep it sane, I am still not convinced that a 
> formulaic relationship between these elements always makes sense.

I'm not convinced either, but Jaime's lighting is always better than mine, 
so I don't argue.  Plus it makes my life simpler (biggest reason). ;-)

Incidentally, I looked up a demo scene of his, and he goes by the 2nd 
component of reflection (which is usually the highest), which would make it 
diffuse 0.85 in your case.  But with rgb 0, I don't think it matters, as 
you've already stated.

>
> I was introducing my daughter to raytracing just the other night.  We were 
> giving a sphere, with no finish specified, different colors just to 
> demonstrate how the color vector worked.  I was trying to get her to guess 
> how to get yellow by introducing the concept that yellow is really 
> not-blue.  So first I had to demonstrate that white is <1,1,1>. We did the 
> render.  "It doesn't look white, it looks grey", was her immediate 
> reaction. :(

Some day, when you grow up, you'll realize that there is no such thing as 
rgb 0 and rgb 1, just various shades of rgb 1*A, where A is a value between 
0 and 1, non-inclusive*.  ;-)

>
> With a low rgb, radiosity also is neutralized.  So the only way to get any 
> tones into the shadows is reflection. But even the slightest amount of 
> reflection gives a hard-shiny look.
>
> About the bottom of the shoe. ("Bottom" is the correct term.) Yes, if it 
> was made of leather it would show wear and have tan patches.  If not, then 
> it would be some homogenous material other than leather and therefore show 
> different surface characteristics.  It is an important question because it 
> may be true that the solution to the problem has to do with providing 
> massive amounts of minute surface detail.  After all, shiny, homogenous, 
> black patent leather is favored by some precisely for its "dark liquid", 
> form-denying properties.

I was just thinking that the bottom might be made of a different material. 
...or it might not...

>
> So the hunt goes on.  But I was interested to peoples reactions to gross 
> adjustments of these factors across the scene in general.
>

If you have the time/patience/computing power, making rotating animations 
can help point out flaws, especially for things such as specular.  From 
certain angles, specular reflections may appear ok, but from others, you 
realize they are too high / too rough / too etc.

Just mentioning some tricks that I've learned.

*I'm thinking of making that my sig.  :-)

-- 
Jeremy
www.beantoad.com

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Jeremy M. Praay wrote:

> I'm not convinced either, but Jaime's lighting is always better than mine, 
> so I don't argue.  

Exactly.

> Incidentally, I looked up a demo scene of his, and he goes by the 2nd 
> component of reflection (which is usually the highest), which would make it 
> diffuse 0.85 in your case.  But with rgb 0, I don't think it matters, as 
> you've already stated.
> 

I will have to study this matter further.


> 
> If you have the time/patience/computing power, making rotating animations 
> can help point out flaws, 

Sometimes brutally so.  I used that technique for my first ever IRTC 
entry.  I was inexperienced at placing objects then.

especially for things such as specular.

Gawd, not specular too.

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Jim Charter wrote:
> Jeremy M. Praay wrote:
>> Jaime recently mentioned "diffuse + reflection = 1". [...]
>
> For a long long time I typically adjusted 
> diffuse/specular/reflection as some sort of loosely conceived division 
> up of a unit whole.  

   Now that you mention it, I was just thinking about specular, and also 
phong, having the same "relation" with diffuse. Re-reading the part of 
the docs about diffuse, seems it accounts for anything that is not 
direct light reflection. As specular and phong both simulate reflection 
of the light sources, seems that also diffuse+specular or diffuse+phong 
should be 1. But we use traditionally specular or phong coupled with 
reflection, so I really don't know what to do with all this...

   Oh... I almost forgot about the original post: I prefer 22 or 23, 
both look very convincing.

--
Jaime

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21

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23 is the best (if I had to buy one pair)
24,25,30 and 31 are very "disco"
27,28 found at Chelsea flea market !


Rene
http://rene.bui.free.fr - online portfolio

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Rene Bui wrote:
> 23 is the best (if I had to buy one pair)

Sold!

> 24,25,30 and 31 are very "disco"

They pulse.

> 27,28 found at Chelsea flea market !
> 

Two for one!  They do look a little rusted over.

> 
> Rene
> http://rene.bui.free.fr - online portfolio
> 
>

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