POV-Ray : Newsgroups : povray.binaries.scene-files : Dakota Red Granite macro - beta #1 Server Time
25 Jul 2021 09:34:12 EDT (-0400)
  Dakota Red Granite macro - beta #1 (Message 11 to 18 of 18)  
<<< Previous 10 Messages Goto Initial 10 Messages
From: Thomas de Groot
Subject: Re: Dakota Red Granite macro - beta #1.1
Date: 18 May 2021 02:24:15
Message: <60a35d8f$1@news.povray.org>
Op 17/05/2021 om 19:42 schreef Bald Eagle:
> Thomas de Groot <tho### [at] degrootorg> wrote:
> 
>> You make an error here I believe. The first expression is /not/ the
>> x-value but the *color_map entry*! And so the last one is /not/ a filter
>> value. Below, this gets wrong as a consequence:
> 
> Nope.
> I converted the entire color map into an array of /4-component/ vectors, with
> the color map entry as the first number.  And, as I anticipated, this might be
> confusing.  Maybe this should be rearranged to have the color map entry be the
> filter, or (better?) constructed as a 2D array?

I need to plunge more seriously into arrays, but yes, I believe a 2D 
array would be better in this context. I shall have a look and try to 
work out something by myself (good practice!). First to cool smoking 
brain cells... :-)

> It was just a quick example of how to not write out the whole color map twice,
> and make any changes easier.
> 
>>
>>> #local C_gr21_DakotaRed_map1 = //the granite colour_map proper
>>> color_map {
>>>     #if (version >= 3.8)
>>>       blend_mode 2
>>>     #end
>>>     #local Entries = dimension_size (CM, 1)-1;
>>>     #for (E, 0, Entries)
>>>     [CM[E].x rgb <CM[E].y, CM[E].z, CM[E].filter>]
>> This line is confusing. How would you write the line above? Like this?
>> (? used for unknown expression):
>>        [CM[E].? rgb <CM[E].x, CM[E].y, CM[E].z>]
>>
>>>     #end
>>> }
>>>
>>
>> Also, in the above example with CSC=1 ('raw' srgb option) should 'rgb'
>> not be 'srgb'? I am getting ab bit lost here.
> 
> That line above is wrong, but for a different reason.
> It's SUPPOSED to be:
>   [CM[E].x Convert  (CSC, SatBoost, BrightBoost, <CM[E].y, CM[E].z,
> CM[E].filter>)]
> 
> That way the one macro gets used for every CSC, and the rgb / srgb / function
> gets implemented in the macro, not directly in the color map.
> I got distracted and made an oopsie.
> 
> See if anything special needs to be done in the full macro so that the srgb
> option works even though SatBoost, BrightBoost are not explicitly specified - in
> other words, an unused default placeholder value just gets passed into the
> macro.
> 
> Attaching file so it's all (hopefully) clearer.
> 

Ok. Going to wrap that up somehow. Thanks for this. I have done very 
little in the way of arrays in the past, so this is a good opportunity 
to get better acquainted.


-- 
Thomas


Post a reply to this message

From: Thomas de Groot
Subject: Re: Dakota Red Granite macro - beta #1.1
Date: 18 May 2021 02:36:07
Message: <60a36057$1@news.povray.org>
Op 17/05/2021 om 12:40 schreef Bald Eagle:
> Thomas de Groot <tho### [at] degrootorg> wrote:
> 
>>> I'm thinking that my suggestion for
>>> #local not_0 = 1/256;
>>> was close, but that would not give a pure black.  Maybe 1/257 to give a pure
>>> black monitor color but still not 0;
>>>
>> I think it is a trivial difference. As Alain said, no real black in
>> nature, and the black pigments here represent micas, which are far from
>> pitch black anyway.
> 
> I suppose it is .. trivial ... but my thought was as a general point, we should
> provide the users with the fullest range of colors as possible, realistic or
> not, so that we don't code another 20 scenes that 20 years from now people with
> throw up their hands and cry "Why did they DO *this*???"
> 
> So I was thinking it would allow the representation of the purest black
> possible, but still not be zero.  What color is a dark hole or a lightless room?
> There may also be scenes later on where people are rendering heightfields, etc,
> and want a pixel rgb that numerically is integer 0.
> 
> Nothing really to do with the present granite, just thinking ahead.
> That's all.
> 

I think there are two tracks here to consider: (1) the use of 'pitch 
black' in pigments and textures, where the use of 1/256 or 1/257 would 
be the way to go; (2) the use of <0,0,0> in a 'geometrical' construction 
like a height_field or, I suppose, an isosurface or a parametric object 
or whatever, where 'true' zero would be a must. this should be clear 
from the onset in any scene. Height_fields in particular certainly make 
good use of 'true' zero. Approximations should be reserved for 
pigments/textures.

-- 
Thomas


Post a reply to this message

From: jr
Subject: Re: Dakota Red Granite macro - beta #1.1
Date: 18 May 2021 06:30:00
Message: <web.60a3966a581f2f6879819d986cde94f1@news.povray.org>
hi,

Thomas de Groot <tho### [at] degrootorg> wrote:
> ... I have done very
> little in the way of arrays in the past, so this is a good opportunity
> to get better acquainted.

an array of 'array mixed' will allow to keep "sets" of parameters together.


regards, jr.


Post a reply to this message

From: Dave Blandston
Subject: Re: Dakota Red Granite macro - beta #1.1
Date: 18 May 2021 06:55:00
Message: <web.60a39c8b581f2f6879416a1f607c1b34@news.povray.org>
Thomas de Groot <tho### [at] degrootorg> wrote:
> I think there are two tracks here to consider: (1) the use of 'pitch
> black' in pigments and textures, where the use of 1/256 or 1/257 would
> be the way to go; (2) the use of <0,0,0> in a 'geometrical' construction
> like a height_field or, I suppose, an isosurface or a parametric object
> or whatever, where 'true' zero would be a must. this should be clear
> from the onset in any scene. Height_fields in particular certainly make
> good use of 'true' zero. Approximations should be reserved for
> pigments/textures.

If I may offer a humble opinion/observation, using a value of 1/256 for the
purpose of multiplying the brightness of an object does not make sense (to me,
anyway) for this reason: Assuming the base scene is lit such that a fully-lit
part of an object will have the same approximate output RGB value as the
corresponding RGB value of the input pigment, a value of 1/256 will result in a
pixel value of 0. In my opinion, that should be considered the true base value.
What is the alternative? 1/256 is arbitrary. Why not 1/317? It's not possible to
foresee what value is actually going to be desired.

Also, even the best monitors don't display pure black anyway. Maybe future
technological developments will change that...

Kind regards,
Dave Blandston
Suggested motto: "With POV-Ray anything is possible, but nothing is easy"


Post a reply to this message

From: Thomas de Groot
Subject: Re: Dakota Red Granite macro - beta #1.1
Date: 18 May 2021 07:51:06
Message: <60a3aa2a$1@news.povray.org>
Op 18-5-2021 om 12:52 schreef Dave Blandston:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>> I think there are two tracks here to consider: (1) the use of 'pitch
>> black' in pigments and textures, where the use of 1/256 or 1/257 would
>> be the way to go; (2) the use of <0,0,0> in a 'geometrical' construction
>> like a height_field or, I suppose, an isosurface or a parametric object
>> or whatever, where 'true' zero would be a must. this should be clear
>> from the onset in any scene. Height_fields in particular certainly make
>> good use of 'true' zero. Approximations should be reserved for
>> pigments/textures.
> 
> If I may offer a humble opinion/observation, using a value of 1/256 for the
> purpose of multiplying the brightness of an object does not make sense (to me,
> anyway) for this reason: Assuming the base scene is lit such that a fully-lit
> part of an object will have the same approximate output RGB value as the
> corresponding RGB value of the input pigment, a value of 1/256 will result in a
> pixel value of 0. In my opinion, that should be considered the true base value.
> What is the alternative? 1/256 is arbitrary. Why not 1/317? It's not possible to
> foresee what value is actually going to be desired.
> 
> Also, even the best monitors don't display pure black anyway. Maybe future
> technological developments will change that...
> 
> Kind regards,
> Dave Blandston
> Suggested motto: "With POV-Ray anything is possible, but nothing is easy"
> 

Well, personally I am no expert on the question, and I prefer to let 
others answer/discuss this point. Who's next? :-)

-- 
Thomas


Post a reply to this message

From: Bald Eagle
Subject: Re: Dakota Red Granite macro - beta #1.1
Date: 18 May 2021 14:00:00
Message: <web.60a4003e581f2f681f9dae3025979125@news.povray.org>
"Dave Blandston" <IsN### [at] protonmailch> wrote:

> If I may offer a humble opinion/observation, using a value of 1/256 for the
> purpose of multiplying the brightness of an object does not make sense (to me,
> anyway) for this reason: Assuming the base scene is lit such that a fully-lit
> part of an object will have the same approximate output RGB value as the
> corresponding RGB value of the input pigment, a value of 1/256 will result in a
> pixel value of 0. In my opinion, that should be considered the true base value.
> What is the alternative? 1/256 is arbitrary. Why not 1/317? It's not possible to
> foresee what value is actually going to be desired.
>
> Also, even the best monitors don't display pure black anyway. Maybe future
> technological developments will change that...

http://news.povray.org/web.607425886a35d6561f9dae3025979125%40news.povray.org

So, the idea here is that we have some "pigment" color value that defines the
visible color.

If it were considered in a vacuum, where everything would be static, and you'd
be directly mapping that value onto the monitor, then all would be fine.

The complication comes in when other things begin to happen in the scene, and
you wonder why your scene looks weird / not good / off.

And that's where the not_0 thing comes into play.  We want to define a non-zero
color component for each of the channels.  If I focus the rays of the sun onto a
black object with a big parabolic mirror or magnifying glass, then there needs
to be - from a computational standpoint, some way of calculating what the
resulting object would look like under those conditions.  And that is usually a
result of multiplying the object pigment by the light source.  If I define
reflection, metallic, or shine a red light on something, then a zero r channel
value would give a 0 * whatever result.  Zero.   And that's not going to give
you "the expected" visual result.  The same thing happens with radiosity.  I
might have a "blue" wall, but when white light reflected off of red and green
objects hit the wall, they affect the perceived color of the wall - and so you
need a non-zero value for the r and g color channels.  There needs to be
_something_ there to get multiplied, and I just figured that a value _just_
below the perceptible / representable threshold value would be a good place to
start.

You are correct, that it IS arbitrary, however it is a value that has a basis /
reason as the current starting point.  I just wanted to make sure it was
actually below the threshold and not above it.



Inigo Quilex worked for Pixar, so I'm making the grounded presumption that he
learned a lot of good professional tricks / best practices.

https://www.youtube.com/channel/UCdmAhiG8HQDlz8uyekw4ENw

And Martijn Steinrucken also seems to really know his way around the inner
workings of colors, lighting, and reflections.

https://www.youtube.com/c/TheArtofCodeIsCool/videos


So if you have a few hours, they both mention this point in their videos
multiple times, and might possibly do a quick few lines of throwaway code that
they execute to demonstrate the concept.  Somewhere.


Post a reply to this message

From: Dave Blandston
Subject: Re: Dakota Red Granite macro - beta #1.1
Date: 19 May 2021 03:45:00
Message: <web.60a4c1c6581f2f6879416a1f607c1b34@news.povray.org>
"Bald Eagle" <cre### [at] netscapenet> wrote:
> So if you have a few hours, they both mention this point in their videos
> multiple times, and might possibly do a quick few lines of throwaway code that
> they execute to demonstrate the concept.  Somewhere.

OK I'm a believer in "Not_0" now (even without spending hours researching).

One other consideration (not a suggestion, just a thought) might be to allow a
margin of error since a value of 1/256 seems to indicate that the intended
result is a value of 0 barring any of the conditions you mentioned. So if the
lighting is even the slightest bit too bright then an unintentional "1" could
result. So perhaps a default value with a little "wiggle room" might be
appropriate, like 1/265 since it's an arbitrary starting point anyway.

Kind regards,
Dave Blandston
Suggested motto: "With POV-Ray anything is possible, but nothing is easy"


Post a reply to this message

From: Thomas de Groot
Subject: Re: Dakota Red Granite macro - beta #1.1
Date: 20 May 2021 02:07:13
Message: <60a5fc91$1@news.povray.org>
Op 19/05/2021 om 09:44 schreef Dave Blandston:
> "Bald Eagle" <cre### [at] netscapenet> wrote:
>> So if you have a few hours, they both mention this point in their videos
>> multiple times, and might possibly do a quick few lines of throwaway code that
>> they execute to demonstrate the concept.  Somewhere.
> 
> OK I'm a believer in "Not_0" now (even without spending hours researching).
> 
:-)

> One other consideration (not a suggestion, just a thought) might be to allow a
> margin of error since a value of 1/256 seems to indicate that the intended
> result is a value of 0 barring any of the conditions you mentioned. So if the
> lighting is even the slightest bit too bright then an unintentional "1" could
> result. So perhaps a default value with a little "wiggle room" might be
> appropriate, like 1/265 since it's an arbitrary starting point anyway.
> 
Seems a good idea. Done for next beta.


-- 
Thomas


Post a reply to this message

<<< Previous 10 Messages Goto Initial 10 Messages

Copyright 2003-2021 Persistence of Vision Raytracer Pty. Ltd.