On Thu, 14 Sep 2000 15:58:50 -0700, Xplo Eristotle
<inq### [at] unforgettablecom> wrote:

>Chris Huff wrote:
>> This would be better done as a post_process filter(since that is exactly
>> what it is). You could probably implement it with the existing add,
>> multiply, subtract, divide, and exponent filters.
>
>Uh.. no, it wouldn't. If you "photo" post-process an image with only 8
>bits of luminance, you're going to end up with hideous round-off errors,
>especially at the ends of the scale (if I've been reading this stuff right).

I am betting 50-50 that the post-process in MP uses the unclipped
color values which are defined as double (I think) or maybe float.


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] usanet
TAG      e-mail : pet### [at] tagpovrayorg

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Chris Huff wrote:
> 
> In article <39C157EB.210EB232@unforgettable.com>,
> inq### [at] unforgettablecom wrote:
> 
> > Besides, part of the problem is that POV-Ray is incapable of handling
> > scenes with high levels of contrast which are meaningful to the human
> > eye. If it can't generate this much contrast - even algorithmically,
> > before it ever puts pixel to screen - then how can it possibly extract
> > an accurate simulation from the crippled data?
> 
> It stores colors as single-precision floating point values...isn't that
> enough? It is certainly far more than 8-bit...

Well, see, that's news to me! ^^;

I'm not a conventional programmer, so I never bothered to look at the
source code.

-Xplo

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In article <sst2ssc5jcnh9kh4rl0l5g1u8fq4rn7lj3@4ax.com>, Peter Popov 
<pet### [at] usanet> wrote:

> I am betting 50-50 that the post-process in MP uses the unclipped
> color values which are defined as double (I think) or maybe float.

You bet mostly right...they are defined as arrays of single-precision 
floats, one per color component. And the unclipped, full precision 
values are the ones used in the post process filters, one of the biggest 
advantages over editing in a separate program(the additional available 
information isn't as big an advantage, since you could also make a patch 
to output it as separate data images to be used by an external program).

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><

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Ken wrote:

> Josh English wrote:
> >
> > Wow. Gilles Tran admits to "no artistical merit" and still produces an amazing
> > image.
>
> Artistic merit has just been redefined.

yup, sounds like what they do
"The poverty rate in America is now 0.0%!"

--
David Fontaine  <dav### [at] faricynet>  ICQ 55354965
My raytracing gallery:  http://davidf.faricy.net/

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Xplo Eristotle wrote:

> It isn't? Boy, I sure must suck then.. I've had reasonable success
> lighting a room with "artificial" lighting, but as soon as I try to open
> a door or window and shine sunlight in, my lighting model goes straight
> to hell.
>
> I suppose I could adjust the lighting so that the sunlight doesn't
> create numbers greater than one, but then my other lights get dimmed
> into nonexistence and so does my radiosity. A patch that bends the
> luminance in 48 bits *might* fix this, but it seems like a ghastly way
> to develop a scene, and I think some kind of adaptive scaling would be
> much, much better than clipping.

Well, if you want to get technical, it would be physically accurate to have those
artificial lights dimmed into nonexistence (assuming enough color depth). Then you
would just turn off the room lights, display the pic on a black background and stare
at it until your pupils have dialated enough... of course, the other problem is that
you'll never get realistic intensities, black levels or contrasts on a CRT.

--
David Fontaine  <dav### [at] faricynet>  ICQ 55354965
My raytracing gallery:  http://davidf.faricy.net/

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David Fontaine wrote:
> 
> Xplo Eristotle wrote:
> 
> > It isn't? Boy, I sure must suck then.. I've had reasonable success
> > lighting a room with "artificial" lighting, but as soon as I try to open
> > a door or window and shine sunlight in, my lighting model goes straight
> > to hell.
> >
> > I suppose I could adjust the lighting so that the sunlight doesn't
> > create numbers greater than one, but then my other lights get dimmed
> > into nonexistence and so does my radiosity. A patch that bends the
> > luminance in 48 bits *might* fix this, but it seems like a ghastly way
> > to develop a scene, and I think some kind of adaptive scaling would be
> > much, much better than clipping.
> 
> Well, if you want to get technical, it would be physically accurate to have those
> artificial lights dimmed into nonexistence (assuming enough color depth). Then you
> would just turn off the room lights, display the pic on a black background and stare
> at it until your pupils have dialated enough... of course, the other problem is that
> you'll never get realistic intensities, black levels or contrasts on a CRT.

I think you're missing the point. To avoid clipping problems, I have to
design my scene with extremely low light levels (read: "huh? there's
nothing in the image except this white square") and *hope* that it'll
look better once it gets adjusted. It would make a lot more sense to be
able to work at normal light levels, so I can actually SEE what I'm
doing when I test.

Or I could do what I'm actually doing now, which is to use only
artificial lighting, which ISN'T WHAT I WANTED TO DO. :P

-Xplo

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Gilles Tran wrote:

> Disclaimer : this scene has no artistical merit whatsoever.

This is a breathtaking scene. I haven't read all the comments below yet, but
let me add my 2 cents.

Your modest comment is so dripping with irony as to be almost immodest!

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Xplo Eristotle wrote:

> I think you're missing the point. To avoid clipping problems, I have to
> design my scene with extremely low light levels (read: "huh? there's
> nothing in the image except this white square") and *hope* that it'll
> look better once it gets adjusted. It would make a lot more sense to be
> able to work at normal light levels, so I can actually SEE what I'm
> doing when I test.

I wasn't totally serious. :)
Still, it's up to the user to keep their light within an acceptable range.
(BTW if you were doing an anim where a window/door opens, you could have the scene
wash
out and gradually come back into normal range simulating pupil constriction...)

--
David Fontaine  <dav### [at] faricynet>  ICQ 55354965
My raytracing gallery:  http://davidf.faricy.net/

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David Fontaine wrote:
> 
> Xplo Eristotle wrote:
> 
> > I think you're missing the point. To avoid clipping problems, I have to
> > design my scene with extremely low light levels (read: "huh? there's
> > nothing in the image except this white square") and *hope* that it'll
> > look better once it gets adjusted. It would make a lot more sense to be
> > able to work at normal light levels, so I can actually SEE what I'm
> > doing when I test.
> 
> I wasn't totally serious. :)
> Still, it's up to the user to keep their light within an acceptable range.

It's the notion of "acceptable range" that bothers me.

-Xplo

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Xplo Eristotle wrote:

> It's the notion of "acceptable range" that bothers me.

Maybe POV could save all the pixels, then scale it so the brightest one is equal
to a maximum_intensity...

--
David Fontaine  <dav### [at] faricynet>  ICQ 55354965
My raytracing gallery:  http://davidf.faricy.net/

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