"Kenneth" <kdw### [at] earthlinknet> wrote:
> This is something I posted recently, just as a comment at another,
> somewhat-related news thread; but I had been wanting to suggest it for some
> time, so  I thought I'd give it its own post...
>
> I believe that an alternate
> type of focal blur would be visually/aesthetically useful, one that blurs
> the image only from the camera to the
> object/point of interest, then keeps the distance beyond that sharp. I'm
> thinking along the lines of "hyperfocal distance" in a real camera lens,
> but more extreme. It probably has no analog in the real world of lenses, but
> I believe (and this is subjective, of course) that it
> would help to make the blurring more realistic in some circumstances-- as
> for outdoor scenes on a
> bright and sunny day.  The blurring that POV currently uses sometimes makes
> objects in a scene look "small" or miniaturized--a sharp zone surrounded by
> a sea of blurriness.   I realize that real lenses do that (!), and that it's
> more pronounced when making close-up photos, depending on the lens aperture.
>  But I guess that's the point I'm trying to make: that the current focal
> blur has a tendency to make all scenes look like they are close-ups. But
> the way we "see" the world, things close to our eyes are blurry, things far
> away are sharp (or at least, our brains seem to make it so!)
>
> I'm thinking that implementing such a blur in POV-Ray
> would *only* (?) require that image pixels (or rays) "beyond" the point of
> max
> sharpness not be jittered. As it is now, pixels/rays are jittered (equally?)
> in
> *both* directions relative to the max sharpness point.
>
> Could this be implemented as easily as I imagine?
>
> Ken W.

IIUC the blur is implemeted by shooting rays from random locations to the
focused plane. Maybe you could focus to the infinity (fixed focus cameras
do this) but then you can not focus anything else. You can already do/fake
this by focusing a very distant object (focal_point 1e6*z). Then the only
thing you can change is the aperture.
BTW anything is a close-up relative to the background, just the relative
aperture gets smaller. :-)

one idea might be to refract the ray to one particular direction if it
reaches the focused point but:
1) it's unrealistic
2) what if the ray undergoes a refraction before reaching the focus plane?
It might be difficult to decide the correct direction and might not look
good in some cases. Doing nothing results in e.g. FBing the background
behind a (refractive) window but not if seen directly.

The eye works just like a usual camera with two differences:
-the retina is spherical, not planar. This can simulated by lowering the
aperture around the edges but that's not that important.
-the eye focuses on whatever you look, but not at the same time. When you
watch the clouds, your newspaper is blurred. If you are reading the clouds
are.
This can be simulated by shooting one ray directly and then focusing other
ones on this one if it is far enough, else at the closest focusable point.
However,
--you can also want to focus on the reflections/refractions. You might not
want to focus your window when looking through. Correctly determining the
focal distance through curved surfaces is impossible (but you can pretend
they are completely flat). Another question is, what to focus at, though?
--you still get blurred background in front of an object and the object
blurred in front of the background, just with a sharp line between those
two. Never mind the antialiasing.
--If you don't sample more points when hitting an object far enough you get
no blur of a close-by object when it should contribute below 50% color.
--Simple said, multi-focus cannot be simulated on a static image. The eye
doesn't produce static images, after all. Still you can render series of
images with different focal distances and feed them to a software to
refocus (or use a realtime blurring map, fed with a focused image and a
depthmap, but it doesn't display anything hidden by foreground objects).

All you can do is to use a low aperture (the most correct way), focus the
infinity (i.e. use a fixed focus camera), or not blur at all (or use a
post-processing tool to do so).

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