I made a little test of the post process focal blur feature in MegaPov 0.5.

In the attached image the left frame is a mirror and the right frame is a
glass object (with ior 1.0, but that is irrelevant). The objects in the
middle are "the real things".

As you can see, focal blur may work fine in some scenes, but if you use
large reflecting or refracting surfaces, you get incorrect results. In such
cases it's probably better to use the more correct original focal blur
feature, even though it's much slower.

If I have understand correctly, the incorrect results are caused by the fact
that the PP focal blur feature blurs the image based on the depth of the
*first* surface it hits. So if it hits a mirror or glass object, you get
incorrect results. Unfortunately I don't think it's possible to fix it,
because of how it works, so we will just have to use the slower focal blur
method if we want more correct results.

Now, I think you all already knew this, I just wanted to make an example
scene that showed it very clearly.

Greetings,

Rune

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Attachments:
Download 'focaltest.jpg' (17 KB)

Preview of image 'focaltest.jpg'

"Rune" <run### [at] inamecom> wrote in message
news:393f8bca@news.povray.org...
|
| Now, I think you all already knew this, I just wanted to make an example
| scene that showed it very clearly.

Um, no, not "all" of us.  In fact just a relative few so far probably did.
Except it is one of those things you can deduce from the way other things
work, reflected light and such.
Thanks for the demonstration.
If it indeed were only surface-count related then I don't see why it would be
impossible to increase to 2 or more.  Maybe only the patch writer knows for
sure, among others  :-)

Bob

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> As you can see, focal blur may work fine in some scenes, but if you use
> large reflecting or refracting surfaces, you get incorrect results. In
such
> cases it's probably better to use the more correct original focal blur
> feature, even though it's much slower.
>


The mirror, at least, I think is correct. In real life it wouldn't be
blurred. When the light hits the mirror it will still be sharp, and since
the mirror itself is in focus then that light will make it to the camera in
focus; I think. The glass is more complicated, In this case I think it
should be blurred, but in other cases it could be in focus, like in that
famous closeup photo of  a branch that has drops of dew in which you can see
background flowers clearly, while in the rest of the picture they're
blurred. Has anyone else seen that? Anyway, I hope that made sense.



Regards

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> The mirror, at least, I think is correct. In real life it wouldn't be
> blurred. When the light hits the mirror it will still be sharp, and since
> the mirror itself is in focus then that light will make it to the camera
in
> focus; I think.
*******
   Think again. hehe :)     You had me going there, Ed . . . didn't think
that
was correct but had to get out the digital camera and see.  Not so . . .
that
image in the mirror is farther away than the mirror surface.  ie the
distance
from the eye (camera) to the mirror plus the distance from the mirror to the
object. Those light rays haven't yet been gathered by the lens and focused
on the "film".  Give it a try to prove it - I had to.
   So, the images in the mirror should also be out of focus.  TS

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"Outback" <out### [at] huntelnet> wrote in message
news:393fd043$1@news.povray.org...
| > The mirror, at least, I think is correct. In real life it wouldn't be
| > blurred. When the light hits the mirror it will still be sharp, and since
| > the mirror itself is in focus then that light will make it to the camera
| in
| > focus; I think.
| *******
|    Think again. hehe :)     You had me going there, Ed . . . didn't think
| that
| was correct but had to get out the digital camera and see.  Not so . . .
| that
| image in the mirror is farther away than the mirror surface.  ie the
| distance
| from the eye (camera) to the mirror plus the distance from the mirror to the
| object. Those light rays haven't yet been gathered by the lens and focused
| on the "film".  Give it a try to prove it - I had to.
|    So, the images in the mirror should also be out of focus.  TS

Yeah, but the water drops on a branch sort of thing does focus the distant
surroundings doesn't it?  I should know that with all the pictures I've taken.
Not about to go searching them to find an example though.  Then again it may
be that the droplets only appear to be in focus considering the lensing effect
they have so there is probably a very different out-of-focus range for them.

Bob

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>   Think again. hehe :)     You had me going there, Ed . . . didn't think
>that
>was correct but had to get out the digital camera and see.  Not so . . .
>that
>image in the mirror is farther away than the mirror surface.  ie the
>distance
>from the eye (camera) to the mirror plus the distance from the mirror to
the
>object. Those light rays haven't yet been gathered by the lens and focused
>on the "film".  Give it a try to prove it - I had to.
>   So, the images in the mirror should also be out of focus.  TS
>


I've no experience with camera, but I'm very short sighted (distance
blurred)
If I look at a distant object, then look at the reflection of the distant
object, the reflection is much clearer. Therefore I think that what is
produced
is correct.

Gail
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"Gail Shaw" <gsh### [at] monotixcoza> wrote in message
news:3940a364@news.povray.org...
|
| I've no experience with camera, but I'm very short sighted (distance
| blurred)
| If I look at a distant object, then look at the reflection of the distant
| object, the reflection is much clearer. Therefore I think that what is
| produced
| is correct.

It may be that a lensing effect takes place due to an implied curvature going
on.  That is to say, with an almost point-like lenses such as the eyes viewing
a large area such as a mirror, even though it be flat, there is a distance
variation across the whole surface.  Same as a lens which is also based upon
distance variation.  This is what I was saying before about the water
droplets, the lensing is going to be yet another focal point.  But then I'm
not an optomologist or whatever the name is for lens scientists  8-)

Bob

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Ed Kaiser <eka### [at] camdentdsnet> wrote:
: The mirror, at least, I think is correct. In real life it wouldn't be
: blurred.

  Wrong. It doesn't matter if the image is a mirrored image or directly seen.
If you think about how light rays travel, what's the difference between a
mirror reflecting something and a hole to another room with the inversed
scene? There's no difference. Light will travel in the same way from the
objects to the camera or whatever. A mirror is not a photograph of the scene.
  The default focal blur of povray is physically more correct.

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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>   Wrong. It doesn't matter if the image is a mirrored image or directly
seen.
> If you think about how light rays travel, what's the difference between a
> mirror reflecting something and a hole to another room with the inversed
> scene? There's no difference. Light will travel in the same way from the
> objects to the camera or whatever. A mirror is not a photograph of the
scene.
>   The default focal blur of povray is physically more correct.
>

Yeah, that makes sense.  nevermind.

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