The animation feature of POV-Ray can be used to make it a spectral 
render engine. The basic idea is to render a set of gray-scale images
  - each representing a specific wavelength - and finally combine them 
using the CIE color match function.
To simplify this task I have created a few POV-Ray SDL scripts and some 
examples.
You'll find the download link, some images and more explanation here:

http://www.lilysoft.org/CGI/SR/Spectral%20Render.htm

-Ive

Post a reply to this message

On 20/09/2012 7:24 PM, Ive wrote:
> You'll find the download link, some images and more explanation here:
>
> http://www.lilysoft.org/CGI/SR/Spectral%20Render.htm

Thanks for posting.
The glasses are spectacular but, as much as I’d like to, I don’t have 
the time to experiment with your Spectral Rendering. It is a bit out of 
my league anyway.

I had not seen 'Bist Du noch da' before and for that alone it was worth 
the visit. I have seen and liked 'In The Mood For Love' and will search 
for a copy of Wong Kar-Way’s 2048 or is it 2046? (Do I see a geek’s typo 
;-) )
I also like you music and that is saying something from someone who 
thinks anything after the 18th Century is a bit too modern.
Just Like A William Powell (lookin' for that Myrna Loy) I enjoyed but it 
reminded me of a tune that I just can’t put my finger on.

Bloody Hell! It sounds like a slow tempo Muppets theme. Tell me that I 
am wrong. ;-)


-- 
Regards
     Stephen

Post a reply to this message

On 20/09/12 20:24, Ive wrote:
> The animation feature of POV-Ray can be used to make it a spectral
> render engine. The basic idea is to render a set of gray-scale images
> - each representing a specific wavelength - and finally combine them
> using the CIE color match function. To simplify this task I have
> created a few POV-Ray SDL scripts and some examples. You'll find the
> download link, some images and more explanation here:
>
> http://www.lilysoft.org/CGI/SR/Spectral%20Render.htm
>

   Oh, well...  just what I needed: another very interesting thing which
I don't have the time to try out, but which I will surely try out anyhow. ;)

   BTW, I love POV-Ray... and your usage of it here shows exactly why:
it's an endless source of fun and surprises.



P.S.: The typical "Great work!" remark falls short here...

--
Jaime

Post a reply to this message

<sigh>
Why is life so short?
Why have days only 24 hours?
Why is there real life?
Why do I love POV-Ray so much?

Thomas

Post a reply to this message

Am 20.09.2012 22:35, schrieb Stephen:
> The glasses are spectacular but, as much as I’d like to, I don’t have
> the time to experiment with your Spectral Rendering. It is a bit out of
> my league anyway.
>
Don't say that. I've spend a lot of time making its usage intuitive. 
Maybe I failed but I would welcome feedback on that matter to improve 
my didactic skills - I know that I suck in explaining things.

> I had not seen 'Bist Du noch da' before and for that alone it was worth
> the visit. I have seen and liked 'In The Mood For Love' and will search
> for a copy of Wong Kar-Way’s 2048 or is it 2046? (Do I see a geek’s typo
> ;-) )
Aaargh! You are so right! Why the heck does 2048 look so much more 
natural to me ;)

> I also like you music and that is saying something from someone who
> thinks anything after the 18th Century is a bit too modern.
You've mentioned this before and I still find it surprising. Especially 
since I do listen to almost all kinds of music of different styles and 
era but I'll have to admit that the 18th and 19th century is the deepest 
gap within my musical horizon. Well, I know all the "hits" all the 
symphonies and all the stuff everybody knowns but it fails to touch me. 
On the other hand, just recently I discovered Mozart's string quintets 
and I really do love them. Maybe a question of getting older?


> Just Like A William Powell (lookin' for that Myrna Loy) I enjoyed but it
> reminded me of a tune that I just can’t put my finger on.
>
> Bloody Hell! It sounds like a slow tempo Muppets theme. Tell me that I
> am wrong. ;-)
>
Haven't heard the Muppets theme since over a decade but I guess you are 
not wrong ;)
Actually the main theme of "Just Like A William Powell" is based on the 
typical "roaring 20ies" Charleston chord progression and I think the 
Muppets-theme uses the same chords.
But the piano bridge between the verses of "...William Powell" cites a 
famous German tune from the 20ies (or 30ies, not sure) called "Ich 
brauche keine Millionen, mir fehlt kein Pfennig zum Glück" (rough 
translation: "Don't need millions, don't miss a penny for 
happiness/luck". Finally the instrumental part is bases on "Katz' Rag" 
(named after the composer) and this was one of the very first tunes I 
played on acoustic guitar when I was learning ragtime finger-picking 
style. To put it like John Renbourn (one of my favorite British 
guitarists): "I've always tried to play like Big Bill Broonzy - and I'm 
still trying!"

For short, as I have actually nothing to say and do not consider myself 
an artist I do with music the same as I do with my POV-Ray images: pack 
them full with tiny references and citations in an attempt to make them 
appear more interesting, but I guess it is not working that way, 
...nonetheless I'll keep trying.

-Ive

Post a reply to this message

Am 21.09.2012 11:11, schrieb Jaime Vives Piqueres:

>    Oh, well...  just what I needed: another very interesting thing which
> I don't have the time to try out, but which I will surely try out
> anyhow. ;)

I'm sorry for that ;)

>    BTW, I love POV-Ray... and your usage of it here shows exactly why:
> it's an endless source of fun and surprises.
>
Yes, the same here! Especially POV-Ray's scripting power makes it 
possible to always find new things to explore. On the other hand (and 
just to mention it) "pro" render engines (V-Ray and the like...) use 
spectral rendering since years.

- Ive

Post a reply to this message

Am 21.09.2012 13:23, schrieb Thomas de Groot:
> <sigh>
> Why is life so short?
> Why have days only 24 hours?
> Why is there real life?
> Why do I love POV-Ray so much?
>
While I understand that these questions are just rhetoric I still feel 
tempted to answer all of them. But as this goes completely OT just 
number three: Because otherwise - for the lack of recreation - humankind 
would be extinct within a few years.

;) -Ive

Post a reply to this message

Ive <ive### [at] lilysoftorg> wrote:
> The animation feature of POV-Ray can be used to make it a spectral
> render engine. The basic idea is to render a set of gray-scale images
>   - each representing a specific wavelength - and finally combine them
> using the CIE color match function.
> To simplify this task I have created a few POV-Ray SDL scripts and some
> examples.
> You'll find the download link, some images and more explanation here:
>
> http://www.lilysoft.org/CGI/SR/Spectral%20Render.htm
>
> -Ive

amazing

Post a reply to this message

On 21-9-2012 16:49, Ive wrote:
> While I understand that these questions are just rhetoric I still feel
> tempted to answer all of them. But as this goes completely OT just
> number three: Because otherwise - for the lack of recreation - humankind
> would be extinct within a few years.

<grin> Absolutely right.

I think you did a great job. I shall do what you ask and try this out, 
and report back if I find something difficult to understand. I have some 
experience in writing tutorials and I know it is not really easy. It 
needs feedback to get better.

Thomas

Post a reply to this message

Ive, I am working on it and writing down a file with comments on your 
tutorial. I hope to be finished today, otherwise tomorrow.

Thomas

Post a reply to this message

Problem with Prism.pov:

unable to find: M_Spectral_Glass

Does not appear in any of the available files.

Thomas

Post a reply to this message

Before all else (I noted it in my comments):

In the command line, +E should be +FE
otherwise it does not save in exr format.

Thomas

Post a reply to this message

Ive, I have the following suggestions for your online tutorial:

1) put the *Prerequisites* block at the top of the tutorial.

2) The command line option +E should be +FE (see Docs) in the tutorial 
and in all .pov files.

3) the *Quick Overview* block is a bit confusing as it mentions all kind 
of processes which are dealt with only later. I suggest to delete this 
block, or – better – to include it at the beginning of the *Some Hints* 
block.

4) In the *First Step* block, ColorChecker.pov does not render the shown 
image, strictly speaking. This is done by SpectralComposer.pov. I 
suggest to change the first paragraph to something like: “Render the 
file ColorChecker.pov animation. This will produce a series of 
grey-scale images of the GretagMacbeth(tm) ColorChecker Chart.”. Below, 
change the corresponding text: “...will create the final PNG image shown 
above. “

5) For better understanding just tell the user to uncomment #declare 
FName = "ColorChecker"; and to comment out #declare FName = 
"Diffraction"; That would be more comprehensive / less confusing.

Thomas

Post a reply to this message

Am 22.09.2012 13:47, schrieb Thomas de Groot:
> Ive, I have the following suggestions for your online tutorial:
>
> 1) put the *Prerequisites* block at the top of the tutorial.
>
> 2) The command line option +E should be +FE (see Docs) in the tutorial
> and in all .pov files.
>
> 3) the *Quick Overview* block is a bit confusing as it mentions all kind
> of processes which are dealt with only later. I suggest to delete this
> block, or – better – to include it at the beginning of the *Some Hints*
> block.
>
> 4) In the *First Step* block, ColorChecker.pov does not render the shown
> image, strictly speaking. This is done by SpectralComposer.pov. I
> suggest to change the first paragraph to something like: “Render the
> file ColorChecker.pov animation. This will produce a series of
> grey-scale images of the GretagMacbeth(tm) ColorChecker Chart.”. Below,
> change the corresponding text: “...will create the final PNG image shown
> above. “
>
> 5) For better understanding just tell the user to uncomment #declare
> FName = "ColorChecker"; and to comment out #declare FName =
> "Diffraction"; That would be more comprehensive / less confusing.
>

Thomas, thank you very much!
This is very helpful and I've corrected already all the "critical 
errors" within both the web.page and the zip-file:
+FE everywhere and M_Spectral_Glass from Prism.inc has changed to 
M_Spectral_Filter.
And I will also follow your advises but it might take some time because
literally I just hear RealLife(tm) urgent calling from outside...

... more later

- Ive

Post a reply to this message

On 22-9-2012 14:04, Ive wrote:
> Thomas, thank you very much!
> This is very helpful and I've corrected already all the "critical
> errors" within both the web.page and the zip-file:
> +FE everywhere and M_Spectral_Glass from Prism.inc has changed to
> M_Spectral_Filter.
> And I will also follow your advises but it might take some time because
> literally I just hear RealLife(tm) urgent calling from outside...
>
> ... more later
>

You are welcome; glad to have been of help. If I find something else 
I'll tell you.

I am going to play some more with your macros. There are some 
interesting possibilities and the results are very nice.

Thomas

Post a reply to this message

On 21/09/2012 3:40 PM, Ive wrote:

> Don't say that. I've spend a lot of time making its usage intuitive.
> Maybe I failed but I would welcome feedback on that matter to improve my
> didactic skills - I know that I suck in explaining things.
>

No, no. It is just my time is so limited nowadays. But a direct appeal 
for feedback cannot be ignored.


> Aaargh! You are so right! Why the heck does 2048 look so much more
> natural to me ;)
>

Because 2048 is 2^11, I would think.

>> I also like you music and that is saying something from someone who
>> thinks anything after the 18th Century is a bit too modern.


> You've mentioned this before and I still find it surprising. Especially
> since I do listen to almost all kinds of music of different styles and
> era but I'll have to admit that the 18th and 19th century is the deepest
> gap within my musical horizon. Well, I know all the "hits" all the
> symphonies and all the stuff everybody knowns but it fails to touch me.
> On the other hand, just recently I discovered Mozart's string quintets
> and I really do love them. Maybe a question of getting older?
>
>

I might be exaggerating a bit. I don’t like 20th Century “classical” 
music with maybe the exception of Benjamin Britain.
You should maybe give Mozart’s piano for 4 hands a listen. Bach and 
Handel transport me.


>> Bloody Hell! It sounds like a slow tempo Muppets theme. Tell me that I
>> am wrong. ;-)
>>
> Haven't heard the Muppets theme since over a decade but I guess you are
> not wrong ;)
> Actually the main theme of "Just Like A William Powell" is based on the
> typical "roaring 20ies" Charleston chord progression and I think the
> Muppets-theme uses the same chords.
> But the piano bridge between the verses of "...William Powell" cites a
> famous German tune from the 20ies (or 30ies, not sure) called "Ich
> brauche keine Millionen, mir fehlt kein Pfennig zum Glück" (rough
> translation: "Don't need millions, don't miss a penny for
> happiness/luck". Finally the instrumental part is bases on "Katz' Rag"
> (named after the composer) and this was one of the very first tunes I
> played on acoustic guitar when I was learning ragtime finger-picking
> style. To put it like John Renbourn (one of my favorite British
> guitarists): "I've always tried to play like Big Bill Broonzy - and I'm
> still trying!"
>

Thank you for that. I have just spent about an hour listening to Marika 
Rökk. I loved this clip on you tube:
http://www.youtube.com/watch?v=NOc8zFCzxno


> For short, as I have actually nothing to say and do not consider myself
> an artist I do with music the same as I do with my POV-Ray images: pack
> them full with tiny references and citations in an attempt to make them
> appear more interesting,

It works for me.

> but I guess it is not working that way,

I wouldn't say that.


> ....nonetheless I'll keep trying.
>

Good! Please do.
:-D

-- 
Regards
     Stephen

Post a reply to this message

On 22/09/2012 8:00 PM, Stephen wrote:
>>
>
> No, no. It is just my time is so limited nowadays. But a direct appeal
> for feedback cannot be ignored.

Your Spectral Rendering with the updated instructions is quite simple to 
use but I need to work on lights and materials.

I posted an image of one of your favourite beasties in p.b.i. I 
decimated the mesh to speed up the rendering time. But actually it was 
the settings in the original scene that made it take so long to render. 
(It might have been the combination of light fade power, max_trace_level 
and mesh)
Anyway I need to get my head round Jamie’s Lightsys etc.



-- 
Regards
     Stephen

Post a reply to this message

Am 22.09.2012 21:00, schrieb Stephen:
>
> Thank you for that. I have just spent about an hour listening to Marika
> Rökk. I loved this clip on you tube:
> http://www.youtube.com/watch?v=NOc8zFCzxno
>
Wow. Marika Rökk, thats a surprise ;)
Note that this video is part of a documentary and those NS "Kraft durch 
Freude" scenes are not part of the movie. Personally I do not like this 
kind of editing as especially this movie cannot be considered as NS 
propaganda flick - after all it features American jazz and tap-dance!
But on the other hand she did participate in 3rd Reich propaganda movies 
and - like Leni Riefenstahl - always claimed that she was just and 
artist and did know nothing ...

-Ive

Post a reply to this message

Am 22.09.2012 16:16, schrieb Thomas de Groot:

> I am going to play some more with your macros. There are some
> interesting possibilities and the results are very nice.
>
> Thomas
>

Have just seen your TC entry and thought I catch you here. As usual I 
enjoyed it to follow the meanwhile familiar personal from Gancaloon but 
what immediately did catch my eye: the mud seems to be more shiny than 
the gold. In case this is not on purpose (well symbolism and such) you 
might want to do something about it ;)

-Ive

Post a reply to this message

On 24-9-2012 6:32, Ive wrote:
> Have just seen your TC entry and thought I catch you here. As usual I
> enjoyed it to follow the meanwhile familiar personal from Gancaloon but
> what immediately did catch my eye: the mud seems to be more shiny than
> the gold. In case this is not on purpose (well symbolism and such) you
> might want to do something about it ;)
>

Caught me. You are not wrong indeed. :-)

The problem is the gold. I finally opted to switch the finish{} off as 
the result was a white, over shiny mass, and I wanted at least the gold 
/colour/ to be visible. Even so, it is not entirely to my taste but as 
so often, I get impatient with the scene and want it over with.

One solution would probably be to get some shadow over it in order to 
block the direct sun light.

For the gold texture, I used golds_37.inc, similar to golds.inc, only 
with srgb instead of rgb.

Thomas

Post a reply to this message

On 24-9-2012 9:24, Thomas de Groot wrote:
The problem is the gold.

Well, I seem to have been wrong with that too. A new test shows that the 
finish can nicely be used. It was probably in an earlier stage of scene 
building.

I shall make an update of the scene.

Thanks for pushing me :-)

Thomas

Post a reply to this message

Ive <ive### [at] lilysoftorg> wrote:
> Am 22.09.2012 21:00, schrieb Stephen:
> >
> > Thank you for that. I have just spent about an hour listening to Marika
> > Rökk. I loved this clip on you tube:
> > http://www.youtube.com/watch?v=NOc8zFCzxno
> >
> Wow. Marika Rökk, thats a surprise ;)


Well I did enjoy jazz and blues at one time and I can listen to it occasionally.

> Note that this video is part of a documentary and those NS "Kraft durch
> Freude" scenes are not part of the movie.

The last scene being in colour was a bit of a giveaway. :-)

> Personally I do not like this
> kind of editing as especially this movie cannot be considered as NS
> propaganda flick - after all it features American jazz and tap-dance!

I understand you not liking it as it does hark back to those days. But for me it
is a mix of old fashioned movie and naive “health and efficiency” with your
clothes on. Although Jazz was banned in Germany during the NS years. I believe
that Goebbels encouraged a home grown film industry which included  German
“Swing” bands.

> But on the other hand she did participate in 3rd Reich propaganda movies
> and - like Leni Riefenstahl - always claimed that she was just and
> artist and did know nothing ...
>
I do sympathise in a way. It is not as if she were pitchforking babies into a
truck, just keeping up moral of the folk at home.
Anyway I cannot get that tune out of my head. I am sure that I have heard it in
English from about the same period.

Stephen

Post a reply to this message

Done a new render with finish{} added to the gold.

Thomas

Post a reply to this message

Thomas de Groot <tho### [at] degrootorg> wrote:
> Done a new render with finish{} added to the gold.
>

How about a bit more red and a couple of small lens flares?

Stephen

Post a reply to this message

On 24-9-2012 16:26, Stephen wrote:
>
> How about a bit more red and a couple of small lens flares?
>

As far as the texture is concerned, I just took one of the golds 
available in the golds.inc. Possibly others contain more or less red. I 
think I shall keep it as is.

I am not too keen on lens flares, especially in this context. I have 
been musing about some blooming or even stars, but in the end abandoned 
the idea as a bit too artificial.

Thomas

Post a reply to this message

Hi all,

following Thomas' advice I have rewritten the "Spectral Rendering" page 
and hope it is now more comprehensive.
As soon as I'll find the time there is more to come ...

-Ive

Post a reply to this message

Am 24.09.2012 16:02, schrieb Thomas de Groot:
> Done a new render with finish{} added to the gold.
>
Hm, I fail to notice any improvement :(

Having not used any of the standard texture include files myself since 
decades I took a quick look at golds.inc and assume you did replace the 
P_Gold statements by
#declare P_Gold1 = srgb CVect1;
...and so on, right?

Well, I have sworn to keep my mouth shut on this topic but I simply 
can't help it. As I have stated multiple times all "color math" works 
only as expected within a linear color space (and doing this kind of 
math myself very often is one of the reasons I advocate for 
assumed_gamma 1.0 since decades).
Now the author of golds.inc does apply a lot of mathematical operations 
on this declared color vectors afterwards - but when this vectors are 
already defined as non-linear srgb values all these operations are 
pretty pointless and the final textures will never look like expected.

And to get even a bit on topic ;) you might find the M_Gold macro with 
its sub-macro calls that are used for *Preview* rendering useful (and 
with a high reflective value like M_Gold(0.9) ) as they give under all 
lighting conditions fairly realistic results.

-Ive

Post a reply to this message

On 25-9-2012 20:08, Ive wrote:
> Hm, I fail to notice any improvement :(

Well, I did, some... :-)

>
> Having not used any of the standard texture include files myself since
> decades I took a quick look at golds.inc and assume you did replace the
> P_Gold statements by
> #declare P_Gold1 = srgb CVect1;
> ...and so on, right?

Yep.

>
> Well, I have sworn to keep my mouth shut on this topic but I simply
> can't help it. As I have stated multiple times all "color math" works
> only as expected within a linear color space (and doing this kind of
> math myself very often is one of the reasons I advocate for
> assumed_gamma 1.0 since decades).
> Now the author of golds.inc does apply a lot of mathematical operations
> on this declared color vectors afterwards - but when this vectors are
> already defined as non-linear srgb values all these operations are
> pretty pointless and the final textures will never look like expected.

In fact, I do not see any difference, but I see your point.

>
> And to get even a bit on topic ;) you might find the M_Gold macro with
> its sub-macro calls that are used for *Preview* rendering useful (and
> with a high reflective value like M_Gold(0.9) ) as they give under all
> lighting conditions fairly realistic results.

So... where is this M_Gold() located? I cannot find it  :-(


Thomas

Post a reply to this message

On 26-9-2012 9:52, Thomas de Groot wrote:
> So... where is this M_Gold() located? I cannot find it  :-(

OK. Found it. My brain is sluggish (it's Wednesday, don't ask me why).

Thomas

Post a reply to this message

On 25-9-2012 20:08, Ive wrote:
> And to get even a bit on topic ;) you might find the M_Gold macro with
> its sub-macro calls that are used for *Preview* rendering useful (and
> with a high reflective value like M_Gold(0.9) ) as they give under all
> lighting conditions fairly realistic results.

I patched in an updated gold nugget bowl with M_Gold(0.9). I first tried 
a reflectance of 0.5 to see the difference.

Thanks for pointing me to the macros. I shall return to them in future 
scenes I am sure.

Thomas

Post a reply to this message

Am 28.09.2012 10:05, schrieb Thomas de Groot:
> I patched in an updated gold nugget bowl with M_Gold(0.9). I first tried
> a reflectance of 0.5 to see the difference.
>
Looks better, methinks ;)

The problem with most of these "old" texture definitions is not only the 
rgb vs. srgb problem. They are simply designed at a time when nobody was 
using radiosity or HDR-lighting (i.e. not necessarily HDRI but 
light_sources with emitting values higher than 1.0). For example 
golds.inc uses an ambient term for the color *calculation* but ambient 
(as part of the finish) gets meanwhile switched off as soon radiosity is 
used.
I'm always did find it easier to use textures that come close to real 
world physics (within the limitations of raytracing) and as such do work 
under all lighting conditions (conventional with/without radiosity and 
radiosity only) instead of tweaking a texture every time I use it.
To me this is not so much about photorealism, it is more about laziness ;)

-Ive

Post a reply to this message

On 28-9-2012 14:33, Ive wrote:
> Am 28.09.2012 10:05, schrieb Thomas de Groot:
>> I patched in an updated gold nugget bowl with M_Gold(0.9). I first tried
>> a reflectance of 0.5 to see the difference.
>>
> Looks better, methinks ;)

Yes, it does indeed.

> The problem with most of these "old" texture definitions is not only the
> rgb vs. srgb problem. They are simply designed at a time when nobody was
> using radiosity or HDR-lighting (i.e. not necessarily HDRI but
> light_sources with emitting values higher than 1.0). For example
> golds.inc uses an ambient term for the color *calculation* but ambient
> (as part of the finish) gets meanwhile switched off as soon radiosity is
> used.

I fully agree. Normally, I rarely use the "out of the box" textures and 
prefer to brew my own. Only for those special cases like gold I am 
rather unsure and tend to use something available, forgetting that they 
are often far from up-to-date.

> I'm always did find it easier to use textures that come close to real
> world physics (within the limitations of raytracing) and as such do work
> under all lighting conditions (conventional with/without radiosity and
> radiosity only) instead of tweaking a texture every time I use it.

You are privileged to know what you are talking about :-)

> To me this is not so much about photorealism, it is more about laziness ;)

An acceptable way of life ;-)

Thomas

Post a reply to this message

Am 28.09.2012 14:33, schrieb Ive:

> I'm always did find it easier to use textures that come close to real
> world physics (within the limitations of raytracing) and as such do work
> under all lighting conditions (conventional with/without radiosity and
> radiosity only) instead of tweaking a texture every time I use it.
> To me this is not so much about photorealism, it is more about laziness ;)

+1

Post a reply to this message

Ive <ive### [at] lilysoftorg> wrote:
> The animation feature of POV-Ray can be used to make it a spectral
> render engine. The basic idea is to render a set of gray-scale images
>   - each representing a specific wavelength - and finally combine them
> using the CIE color match function.
> To simplify this task I have created a few POV-Ray SDL scripts and some
> examples.
> You'll find the download link, some images and more explanation here:
>
> http://www.lilysoft.org/CGI/SR/Spectral%20Render.htm
>
> -Ive

Would this help POV to render caustics any faster?

I ask this because I could not after all my attempts get POV-Ray to render some
caustics scene with chromatic dispersion as fast as Lux Render did (Lux uses
spectral rendering)other than that I would have been so happy to use POV because
of so many other features, but for this particular scene, the speed issue was
really too high of a bottleneck, preventing it to keep the same quality between
the two renderers.

Post a reply to this message

Am 01.01.2013 22:23, schrieb Mr:
> Ive <ive### [at] lilysoftorg> wrote:
>> The animation feature of POV-Ray can be used to make it a spectral
>> render engine. The basic idea is to render a set of gray-scale images
>>    - each representing a specific wavelength - and finally combine them
>> using the CIE color match function.
>> To simplify this task I have created a few POV-Ray SDL scripts and some
>> examples.
>> You'll find the download link, some images and more explanation here:
>>
>> http://www.lilysoft.org/CGI/SR/Spectral%20Render.htm
>>
>> -Ive
>
> Would this help POV to render caustics any faster?
>
> I ask this because I could not after all my attempts get POV-Ray to render some
> caustics scene with chromatic dispersion as fast as Lux Render did (Lux uses
> spectral rendering)other than that I would have been so happy to use POV because
> of so many other features, but for this particular scene, the speed issue was
> really too high of a bottleneck, preventing it to keep the same quality between
> the two renderers.

I'm not sure how Lux does it, but here's one optimization I could 
imagine, which POV-Ray currently doesn't do:

When the generated photon map is evaluated for a dispersed (and hence 
monochromatic) ray from the camera, dispersed (and hence also 
monochromatic) photons with a different wavelength could theoretically 
be ignored (and those typically are a lot if you make ample use of 
high-quality dispersion).

In POV-Ray, the fact that a photon was subject to dispersion (and hence 
is monochromatic) is forgotten in the stored photons map; such photons 
are instead stored just like normal non-dispersed colored photons. Thus, 
POV-Ray needs to evaluate each and every photon even for monochromatic rays.

As Ive's approach only deals with one single wavelength per render 
anyway, it automatically gets that optimization for free. However, for 
non-dispersed rays and photons it loses a lot in terms of performance, 
as it needs to trace such rays and photons over and over again for each 
wavelength even though their trajectory is the same for all wavelengths.

Hard-coding this optimization into POV-Ray should be no big deal; it 
doesn't even need full-fledged spectral color math to work. It would 
probably increase the photons map memory footprint by 20% though.

Post a reply to this message

clipka <ano### [at] anonymousorg> wrote:
> Am 01.01.2013 22:23, schrieb Mr:
> > Ive <ive### [at] lilysoftorg> wrote:
> >> The animation feature of POV-Ray can be used to make it a spectral
> >> render engine. The basic idea is to render a set of gray-scale images
> >>    - each representing a specific wavelength - and finally combine them
> >> using the CIE color match function.
> >> To simplify this task I have created a few POV-Ray SDL scripts and some
> >> examples.
> >> You'll find the download link, some images and more explanation here:
> >>
> >> http://www.lilysoft.org/CGI/SR/Spectral%20Render.htm
> >>
> >> -Ive
> >
> > Would this help POV to render caustics any faster?
> >
> > I ask this because I could not after all my attempts get POV-Ray to render some
> > caustics scene with chromatic dispersion as fast as Lux Render did (Lux uses
> > spectral rendering)other than that I would have been so happy to use POV because
> > of so many other features, but for this particular scene, the speed issue was
> > really too high of a bottleneck, preventing it to keep the same quality between
> > the two renderers.
>
> I'm not sure how Lux does it, but here's one optimization I could
> imagine, which POV-Ray currently doesn't do:
>
> When the generated photon map is evaluated for a dispersed (and hence
> monochromatic) ray from the camera, dispersed (and hence also
> monochromatic) photons with a different wavelength could theoretically
> be ignored (and those typically are a lot if you make ample use of
> high-quality dispersion).
>
> In POV-Ray, the fact that a photon was subject to dispersion (and hence
> is monochromatic) is forgotten in the stored photons map; such photons
> are instead stored just like normal non-dispersed colored photons. Thus,
> POV-Ray needs to evaluate each and every photon even for monochromatic rays.
>
> As Ive's approach only deals with one single wavelength per render
> anyway, it automatically gets that optimization for free. However, for
> non-dispersed rays and photons it loses a lot in terms of performance,
> as it needs to trace such rays and photons over and over again for each
> wavelength even though their trajectory is the same for all wavelengths.
>
> Hard-coding this optimization into POV-Ray should be no big deal; it
> doesn't even need full-fledged spectral color math to work. It would
> probably increase the photons map memory footprint by 20% though.


Thanks! Your explanation is so clear! I would vote for the speed optimization as
I have so much RAM, but I would understand if others disagree. In which case I
would never be able to finish that stupid render. It's not even pretty, just a
comparative test :-)

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