Hi all.  I'm really enjoying PovRay and playing with all the settings for
radiosity, GI, etc.

I'm noticing, though, that there is a subtle element of glow I'm missing
around my sunlit areas, and I don't know how to achieve it.  Here is a
perfect example, rendered in Lightwave, of what I'm trying to achieve:

http://hdri.cgtechniques.com/~sponza/show.php?id=40

Pay attention to the line where the sunlight falls- there is a subtle glow
that adds a tremendous amount of realism.  I'm getting good sunlight in my
Pov scenes, but the line is always perfectly sharp- not glowed and
realistic as in this photo.

Any ideas?

-ZA

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ZainAnak <nomail@nomail> wrote:
> Any ideas?

  What you are after is color-bleeding.

  In photography color-bleeding happens when the amount of light which
hits a spot in the film is too bright for the film. What happens is that
the brightness will "bleed" a bit to its surroundings, making the bright
spot to look like it was glowing.
  A somewhat similar effect in photography can be achieved by using a
filter in front of the lens which scatters the light a bit (this makes
everything glow a bit, not just ultrabright parts).

  In computer renderings these effects are most easily achieved as a
post-processing effect. The official version of POV-Ray does not currently
support any kind of post-processing of the image and thus this effect
is basically not possible. (In some special cases you can fake it, but
not in the general case.)

  At least the 0.x version of MegaPOV supported this kind of post-processing
(or at least close to it), but I don't remember if the latest 1.x version
does.

-- 

                                                          - Warp

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"ZainAnak" <nomail@nomail> wrote in message 
news:web.42dc3438ea2831f43b6b98ba0@news.povray.org...
>
> I'm noticing, though, that there is a subtle element of glow I'm missing

Your question reminds me of what Samuel Benge had done a while back so I 
searched for his post at the web view of binaries.images and found it.

news:40D### [at] hotmailcom

Or at the web view for the whole thread:

http://news.povray.org/40DB67BE.1080608%40hotmail.com

Summed up, his idea was to use the rendering applied over itself but with 
darker parts transparent so only bright parts could be diffused into the 
picture. Not a one-step process, but did what I think you're asking about. 
Unless you only wanted to get better illumination like that seen in the top 
of that left archway of your linked-to image.

Other than that, maybe MegaPOV or another custom POV could do this sort of 
thing. I haven't used anything else but the official versions lately. 
Perhaps someone else might come along with suggestions anyway.

Bob Hughes

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Yup, that's about what I'm looking for.  Thing is, no one in that thread
posted any links to Pov source to achieve it.  Since I'm a total neophyte
to Pov, such source would be very helpful.  Do you know where I can get it?

"Bob Hughes" <bob### [at] charternet> wrote:
> "ZainAnak" <nomail@nomail> wrote in message
> news:web.42dc3438ea2831f43b6b98ba0@news.povray.org...
> >
> > I'm noticing, though, that there is a subtle element of glow I'm missing
>
> Your question reminds me of what Samuel Benge had done a while back so I
> searched for his post at the web view of binaries.images and found it.
>
> news:40D### [at] hotmailcom
>
> Or at the web view for the whole thread:
>
> http://news.povray.org/40DB67BE.1080608%40hotmail.com
>
> Summed up, his idea was to use the rendering applied over itself but with
> darker parts transparent so only bright parts could be diffused into the
> picture. Not a one-step process, but did what I think you're asking about.
> Unless you only wanted to get better illumination like that seen in the top
> of that left archway of your linked-to image.
>
> Other than that, maybe MegaPOV or another custom POV could do this sort of
> thing. I haven't used anything else but the official versions lately.
> Perhaps someone else might come along with suggestions anyway.
>
> Bob Hughes

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"ZainAnak" <nomail@nomail> wrote in message 
news:web.42dd095f9c9b6ebd3b6b98ba0@news.povray.org...
> Yup, that's about what I'm looking for.  Thing is, no one in that thread
> posted any links to Pov source to achieve it.  Since I'm a total neophyte
> to Pov, such source would be very helpful.  Do you know where I can get 
> it?

No, I don't. He had said he might be making a "cleaned up" example available 
but I searched and didn't find that particular thing. Haven't seen Samuel 
around here for a while but he seems to pop in every now and then.

Sorry about the web view link because I thought it was going to show a 
scrollable web page of all the replies there. Just tried it going from my 
reply to you and only got the initial message by Samuel. Sounds like you did 
read each one, although to see all you must go on to the next page (I saw 
three pages in all) so maybe you missed that... or it just didn't make much 
sense to you. Toward the end he tells about it, but yeah, I can understand 
not being able to figure out what was meant exactly.

While I was going over it there again I noticed Tim Nikias' has a glare 
macro, among other great things, which is at:

http://www.nolights.de/download.html

Maybe that would help some, but in trying to duplicate what Samuel had done 
I'm not very successful yet. If I get something to work right in the 
meantime I'll post it later (if I can). Or with any luck somebody else 
already has the solution at hand and could share it. There's always e-mail 
to Samuel Benge, too, if he can be reached.

Bob

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Okay, I managed to come up with the complete script to make that light-bleed 
effect. Best I could, anyhow.

Posting it over at the povray.text.scene-files group. Hopefully it'll be 
passable for what you were wanting to do. You should be able to figure it 
out and make changes. I'm just not positive it can really work right for 
everything. I only tried it with a very simple test scene embedded into the 
scene file. I'm fairly certain this was the same idea Samuel Benge had done, 
just not sure of that either without seeing his script.

BTW, to anyone else out there listening in on this, there seemed to be 
plenty of trouble with adding finish statements to texture mapped textures. 
In the outer texture wrapper, that is, and I can only wonder why. Maybe I'll 
bring that subject up sometime at povray.general.

Good luck with the renderings, ZainAnak!

Bob Hughes

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Thanks!  I have to say, though- I'm having some problems getting it to run
on my machine.  I am a COMPLETELY new user here, so would you mind walking
me through it?  I'm not too sure how to use the command line args
correctly, as when I hit "go" it finishes in 0.4 sec and nothing is
generated.  Anyway, a step-by-step would be much *very* appreciated.

Thanks,
ZA

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"ZainAnak" <nomail@nomail> wrote in message 
news:web.42dd81fa9c9b6ebd3b6b98ba0@news.povray.org...
> I'm not too sure how to use the command line args
> correctly, as when I hit "go" it finishes in 0.4 sec and nothing is
> generated.  Anyway, a step-by-step would be much *very* appreciated.

Okay, happy to try.

I posted the script with it set to render the final image, so be sure you 
change it to CreateImage=yes; first. I expected the comments to make sense, 
probably wasn't a good idea to start it out in reverse with the hope it 
would be changed right away.

Those lines with the //cmd: can be right-clicked and the popup menu will 
show a selection for adding it to the command-line field of the toolbar so 
you don't need to type it in. The first such line sets the output image 
format to PNG uses a path and filename expected to be one of the POV-Ray 
library paths. The folder "renderings" is one I use for all output; however, 
yours could be anywhere else you usually output the renders to.
Just make sure it is also a library path or in the current scene file 
folder, otherwise it won't be found later. Library_Path= can be added to 
your povray.ini via the Tools menu, select 'Edit master POVRAY.INI', and 
look at the end of that text file (folder must already exist!). Close and 
Save the file. You will need to close and run POV again to reset things if 
you choose to do this.

Okay, with that much out of the way you should be able to get a rendered 
example scene if you left it in the script (didn't replace it with your own 
yet). Of course, you could replace that scene (comment it out or delete the 
lines) and either copy and paste your entire scene into it (probably not 
wise for a large file) or collect it all into one or more #include files 
then just add them that way.
Since includes are easier to manage I'll tell more about that.

#if (CreateImage=yes)

#include "yourscene.pov"

#end

is how it would look at its simplist. My example scene with the crackle 
textured sphere has lights and camera within that if/end section but it 
would need to be removed for your own to go there. For now you might want to 
give it a look as is first to be sure it works right.

Next, after rendering that image, you will need to change the command-line. 
So right-click the second //cmd: line in the header comments and select that 
to replace the command-line field with it. Render that way and you should 
see the resulting light-bleed image. Again, be sure you use a path (or none 
to render to default location) and filename you want. As long as the first 
time render has a matching file name that is under the " begin 
light-bleeding part" you should be ok, the second render could be anything.

If this doesn't help completely yet just ask more about it.

Two other things I should mention is image resolution and the 2/3 index 
values of the pigment_map. You're image size for the first rendering will 
probably need to be larger than the second in order to prevent lowering the 
quality. Also, I didn't set this up for anything more than a simple 4:3 
ratio and the scale would need to be adjusted if another ratio is used. 
Likewise, a camera with the proper aspect ratio will be needed. As it is now 
there is no camera defined since it uses a default one at <0,0,0> with 
default parameters.

Maybe you can at least get started on it knowing all this.

Bob Hughes

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Reread my "help" only after posting that reply and saw I left out anything 
about the 2/3 index values found in the pigment_map...! Early morning for 
me, sorry.

I chose two-thirds so that the remaining one-third is the brightest parts of 
the image and would be the only places blended into the original image.

While I'm here again I might as well emphasize the fact that I hadn't even 
used an actual premade scene file to test this effect yet. I have no idea if 
it really looks okay. I'm not 100% positive it works as expected so you'll 
probably know how it really looks before I will.

Bob

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Bob, thanks for all the help!

I had an idea, though.  If you look at the original picture I posted as a
reference, you'll notice that it's a pretty small, well-defined bleed that
occurs at the sun line.  I was wondering- couldn't I achieve this with some
sort of area light setup?  All I really want, after all, is the sun lines
to be a *little* blurrier than normal- I don't want everything bright in
the scene to glare out, like your sample code would do.  Here is my current
light:

light_source {
  <-5000, 4000, 15000>
  color rgb <0.8, 0.4, 0.2>*4.1
}

how would you turn this into a light with slightly fuzzier lines?

Thanks!
-ZA

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