It seems to be focal blur week this week, so I'll ask a question too :)
When I use focal blur in a scene with really bright spots, it seems as if
POV-Ray doesn't use the real brightness, but the clipped values.  For example: a
blurred spot with a brightness > 1 doesn't look any different than a blurred
spot with a brightness = 1.  That's too bad, because I really like the effect in
photographs where focal blurred lights produce bright circles.

Is there something I'm doing wrong, or is this just the way POV-Ray's focal blur
works?

cu!
--
camera{location-z*3}#macro G(b,e)b+(e-b)*(C/50)#end#macro L(b,e,k,l)#local C=0
;#while(C<50)sphere{G(b,e),.1pigment{rgb G(k,l)}finish{ambient 1}}#local C=C+1
;#end#end L(y-x,y,x,x+y)L(y,-x-y,x+y,y)L(-x-y,-y,y,y+z)L(-y,y,y+z,x+y)L(0,x+y,
<.5,1,.5>,x)L(0,x-y,<.5,1,.5>,x)               // ZK http://www.povplace.be.tf

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In article <3d64f851@news.povray.org> , "Zeger Knaepen" 
<zeg### [at] studentkuleuvenacbe> wrote:

> It seems to be focal blur week this week, so I'll ask a question too :) When I
> use focal blur in a scene with really bright spots, it seems as if POV-Ray
> doesn't use the real brightness, but the clipped values.  For example: a
> blurred spot with a brightness > 1 doesn't look any different than a blurred
> spot with a brightness = 1.

Not sure I understand you.  You say you want a stronger white?

> That's too bad, because I really like the effect
> in photographs where focal blurred lights produce bright circles.

You mean lens flares?

    Thorsten

____________________________________________________
Thorsten Froehlich, Duisburg, Germany
e-mail: tho### [at] trfde

Visit POV-Ray on the web: http://mac.povray.org

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On Thu, 22 Aug 2002 17:18:32 +0200, "Thorsten Froehlich"
<tho### [at] trfde> wrote:


>Not sure I understand you.  You say you want a stronger white?

finish { ambient 1000 } for example. If POV averages blur samples
after it clips colors, it will make no difference. If it averages
before clipping colors, then it should work as expected.


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

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> Not sure I understand you.  You say you want a stronger white?
>
> > That's too bad, because I really like the effect
> > in photographs where focal blurred lights produce bright circles.
>
> You mean lens flares?
>

I think I understand what he means and it isn't lens flare.  If you take a
photograph of something and there is a visible lightsource in the background
(assuming that the background is out of focus), the lightsource looks
blurred, but because it is much brighter than the objects around it, it
creates a glowing halo effect.  When creating visible lightsources in POV
you can set a colour value >1, but it gets clipped.  I think what he is
wondering is when you use focal blur, does the colour get clipped before or
after blur sampling?  If it gets clipped after, it would be fine, if before,
then maybe the light colour wouldn't carry enough weight in the blurring and
not look as one should expect.

i.e for simplicity lets look at five numbers averaged:

0.3, 0.5, 0.7, 1.5, 5

clipping after you get:
(0.3+0.5+0.7+1.5+5)/5=1.6 --> 1.0 (clipped)
clipping before you get:
(0.3+0.5+0.7+1+1)/5=0.7

the values greater than 1 lose their appropriate weighting in the average if
they are clipped beforehand

-tgq

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> > It seems to be focal blur week this week, so I'll ask a question too :) When
I
> > use focal blur in a scene with really bright spots, it seems as if POV-Ray
> > doesn't use the real brightness, but the clipped values.  For example: a
> > blurred spot with a brightness > 1 doesn't look any different than a blurred
> > spot with a brightness = 1.
> Not sure I understand you.  You say you want a stronger white?
uhm...
I want to see the bright spots in the blurred parts of the image.  Now they just
get blurred as if they only have a brightness of 1

> > That's too bad, because I really like the effect
> > in photographs where focal blurred lights produce bright circles.
> You mean lens flares?
No, not lensflares.
Wait, I'll search for an image...
http://www.binghamton.edu/home/updates/lights.jpg
You have the lensflare, which produces a glow around the lights, but the
out-of-focus lights in the back look like bright circles.
I don't think that has anything to do with lensflare.

cu!
--
camera{location-z*3}#macro G(b,e)b+(e-b)*(C/50)#end#macro L(b,e,k,l)#local C=0
;#while(C<50)sphere{G(b,e),.1pigment{rgb G(k,l)}finish{ambient 1}}#local C=C+1
;#end#end L(y-x,y,x,x+y)L(y,-x-y,x+y,y)L(-x-y,-y,y,y+z)L(-y,y,y+z,x+y)L(0,x+y,
<.5,1,.5>,x)L(0,x-y,<.5,1,.5>,x)               // ZK http://www.povplace.be.tf

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The colours are clipped before they contribute to the focal blur. You can 
easily change this by commenting out line 2442 in render.cpp which says
'Clip_Colour(C, C);' and recompile povray. I have posted an example to 
p.b.images which shows the result with the modified version in contrast to 
the normal version.

- Micha

-- 
http://objects.povworld.org - the POV-Ray Objects Collection

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In article <s21amu05jvvhomkmpl97mu3avgnddtpr22@4ax.com>,
 Peter Popov <pet### [at] vipbg> wrote:

> finish { ambient 1000 } for example. If POV averages blur samples
> after it clips colors, it will make no difference. If it averages
> before clipping colors, then it should work as expected.

It clips both blur and antialiasing samples. It was apparently to fix 
the case were a "superbright" object is visible, and not clipping the 
samples made it look like it wasn't antialiased. It caused me some real 
problems when I was trying to get decent stars by making them very 
bright so they wouldn't get antialiased into oblivion...there should at 
least be a way to turn it off in my opinion.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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Christopher James Huff <chr### [at] maccom> wrote:
> there should at least be a way to turn it off in my opinion.

  I agree that there should be an option to use unclipped colors
(of course colors should always be clipped when writing the image to file,
but if the option is set, they are not clipped anywhere else).

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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As someone has already located the code-line in
question, would it be that difficult to add another
option like +NCOC (as No Clipping Of Colors)
similiar to +C for Continue trace etc?

It does look like it would be an interesting
option, especially if you would be possible to
define it for objects.
Problem: What about refractions and reflections? You
need to cover those as well...

--
Tim Nikias
Homepage: http://www.digitaltwilight.de/no_lights/index.html
Email: Tim### [at] gmxde

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"Micha Riser" <mri### [at] gmxnet> schreef in bericht
news:3d650e6c@news.povray.org...
> The colours are clipped before they contribute to the focal blur. You can
> easily change this by commenting out line 2442 in render.cpp which says
> 'Clip_Colour(C, C);' and recompile povray. I have posted an example to
> p.b.images which shows the result with the modified version in contrast to
> the normal version.
Interesting image.  Thanks!

Any chance this will be part of the new MegaPov, maybe with an option to turn
clipping on and off?

cu!
--
camera{location-z*3}#macro G(b,e)b+(e-b)*(C/50)#end#macro L(b,e,k,l)#local C=0
;#while(C<50)sphere{G(b,e),.1pigment{rgb G(k,l)}finish{ambient 1}}#local C=C+1
;#end#end L(y-x,y,x,x+y)L(y,-x-y,x+y,y)L(-x-y,-y,y,y+z)L(-y,y,y+z,x+y)L(0,x+y,
<.5,1,.5>,x)L(0,x-y,<.5,1,.5>,x)               // ZK http://www.povplace.be.tf

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