> "Kenneth" <kdw### [at] gmailcom> wrote:
>
>>
>> What I *really* need to do-- for this project and others-- is to buy a shiny
>> sphere, for making a 'light probe' (a non-HDRI version, as my little Canon video
>> camera doesn't shoot HDRI/'raw' images, unfortunately.)
>
> Of course, there's the alternate trick of making, say, five bracketed exposures
> of the mirrored sphere with my 'regular' camera, and then combining those in
> specialized software to make an HDRI image. But I haven't gotten into the HDRI
> world yet, sad to say. "So little time, so MUCH to learn." ;-)
>
>
>
I don't think that any camera can take HDR images natively.
For combining the bracketed images, there is hdrshop. A nice little 
utility just for that purpose. It can also transform a reflective sphere 
probe to a latitude-longitude one that you can then apply to a large 
sphere or sky_sphere using the spherical mapping.


Alain

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On 14/02/2014 8:26 PM, Kenneth wrote:
> "So little time, so MUCH to learn.";-)

Seconded. :-)

-- 
Regards
     Stephen

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> "Kenneth" <kdw### [at] gmailcom> wrote:
>
>>
>> What I *really* need to do-- for this project and others-- is to buy a shiny
>> sphere, for making a 'light probe' (a non-HDRI version, as my little Canon video
>> camera doesn't shoot HDRI/'raw' images, unfortunately.)
>
> Of course, there's the alternate trick of making, say, five bracketed exposures
> of the mirrored sphere with my 'regular' camera, and then combining those in
> specialized software to make an HDRI image. But I haven't gotten into the HDRI
> world yet, sad to say. "So little time, so MUCH to learn." ;-)
>
>

http://news.povray.org/povray.binaries.images/message/%3Cweb.44468657f8d220636c4803960%40news.povray.org%3E/#%3Cweb.44468657f8d220636c4803960%40news.povray.org%3E

   IIRC, that worked nicely, and additionally you have the fun of doing 
it with POV-Ray... :)

--
Jaime

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Jaime Vives Piqueres <jai### [at] ignoranciaorg> wrote:

>
>
http://news.povray.org/povray.binaries.images/message/%3Cweb.44468657f8d220636c4803960%40news.povray.org%3E/#%3Cweb.4
4468657f8d220636c4803960%40news.povray.org%3E
>
>    IIRC, that worked nicely, and additionally you have the fun of doing
> it with POV-Ray... :)
>

That is fascinating!!  Thanks for posting the link; I had not seen it before. I
can certainly make use of Trevor's sophisticated code ideas: Awhile ago, I tried
writing some similar (though inferior) code to do this kind of 'HDRI conversion
in POV-Ray', but got rather bland results. I see now what I was doing wrong.

Thanks! (And to Trevor too!)

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"Robert McGregor" <rob### [at] mcgregorfineartcom> wrote:

>
> I have a 5 inch chrome sphere that I use for that very purpose (plus it looks
> cool on my desk when not in use). Mount your camera on a tripod and take a set
> of bracketed shots, then rotate the tripod ~90 degrees around the sphere and
> take another set of bracketed shots. After you've combined the two bracketed
> imagesets into 2 HDRs you can merge these offset images to eliminate the
> camera/tripod completely from the final shot. Of course, Ive's IC is very useful
> here:
>
> http://www.lilysoft.org/IC/ic_index.htm
>

So the 90-degree image is simply to get a clean area to 'replace' the
camera-plus-photographer in the original straight-on image? That makes perfect
sense. Here's a question, though: Is the *final* light probe ultimately made
from BOTH of those images? (Meaning: Is the 'corrected' straight-on image
somehow combined WITH the (similarly-corrected) 90-degree image to get a light
probe that has MORE environment imagery in it? Or is only the straight-on image
used?)

There's also something *mysterious* about light probes that I still have trouble
grasping: In my research into the subject, several sources stated that the
mirrored ball actually gathers environment imagery from BEHIND itself-- in the
spatial hemisphere out of view of the camera(!)-- implying that the very edges
of the ball pick up the 'hidden' back-side environment. Is that true (or even
possible?)

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> "Robert McGregor" <rob### [at] mcgregorfineartcom> wrote:
>
>>
>> I have a 5 inch chrome sphere that I use for that very purpose (plus it looks
>> cool on my desk when not in use). Mount your camera on a tripod and take a set
>> of bracketed shots, then rotate the tripod ~90 degrees around the sphere and
>> take another set of bracketed shots. After you've combined the two bracketed
>> imagesets into 2 HDRs you can merge these offset images to eliminate the
>> camera/tripod completely from the final shot. Of course, Ive's IC is very useful
>> here:
>>
>> http://www.lilysoft.org/IC/ic_index.htm
>>
>
> So the 90-degree image is simply to get a clean area to 'replace' the
> camera-plus-photographer in the original straight-on image? That makes perfect
> sense. Here's a question, though: Is the *final* light probe ultimately made
> from BOTH of those images? (Meaning: Is the 'corrected' straight-on image
> somehow combined WITH the (similarly-corrected) 90-degree image to get a light
> probe that has MORE environment imagery in it? Or is only the straight-on image
> used?)
>
> There's also something *mysterious* about light probes that I still have trouble
> grasping: In my research into the subject, several sources stated that the
> mirrored ball actually gathers environment imagery from BEHIND itself-- in the
> spatial hemisphere out of view of the camera(!)-- implying that the very edges
> of the ball pick up the 'hidden' back-side environment. Is that true (or even
> possible?)
>
>

When using a mirrored sphere, there is a blind cone right behind it: The 
area of the view hiden from the camera by the sphere itself.
There is also a loss of definition near the edge.

remove the camera, to get a full spherical covering.

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Alain <kua### [at] videotronca> wrote:

>
> When using a mirrored sphere, there is a blind cone right behind it: The
> area of the view hiden from the camera by the sphere itself.
> There is also a loss of definition near the edge.

> remove the camera, to get a full spherical covering.

Thanks, Alain; the idea is finally beginning to make sense to me.

I always like to have a theoretical understanding of how things work; but I have
not yet come across a physical description of how light rays behave as they
strike the circular edge of a mirrored sphere. So here is my own 'thought
experiment': The circular 'edge' can be thought of as an infinite number of tiny
'flat' mirrors, each one aligned *almost* parallel to the camera's line of
sight. Since "angle of incidence = angle of reflection", the reflected light
rays (from the surrounding environment) do indeed come from areas 'behind' the
sphere! :-) (Except for the small missing cone, as you mentioned.)

I tried this experiment by eye, with a flat mirror-- and it works (of course!)
Duh!  It all seems so obvious now.

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BTW, the most important part of this 'matchmoving' scheme was to determine, at
the beginning, what the proper POV-Ray camera ANGLE should be, to best match my
Canon camera's lens angle (at its default 'wide angle' setting, which is how I
shoot most videos.) At first, I thought this would be a simple and
straightforward
process: Take a video of some kind of subject matter that had clearly-seen
'vanishing-point lines', pick a representative still frame from it, then place
some CGI objects in the scene that 'matched' those, along with the proper
perspective (POV-Ray's Screen.inc include file was ideal for doing this.) The
process required quite a few test renders to 'zero in' on the proper matching
lens angles.

But a problem arose when doing the animated matchmoving: POV-Ray's default
perspective camera is a 'perfect pin-hole' camera. A 'real' camera is not; its
lens has spherical aberration, plainly seen at the outer edges of the image.
This discrepancy caused some visual 'sliding' of CG objects against the
background images, at the edges of the frame, as the video camera panned, tilted
and rolled. So I had to find a compromise between the two lens angles, to try
and eliminate this sliding (or at least minimize it)-- essentially by making the
POV-Ray camera lens a bit more of a 'telephoto' lens than it should be. (Meaning
that the 'perspective' of both lenses no longer matches.) But it seems that this
perspective mis-match is far less visually distracting than the (very obvious)
sliding of CG elements.

Here's something interesting: When professional CGI is done for Hollywood
movies, the original 'real' imagery-- with its spherical aberration distortion--
is first UN-distorted in software; then the CG elements are matched to that
(with a 'perfect pinhole-camera'); then the final composite imagery is
RE-distorted to add the spherical aberration back in, to all elements.

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"Kenneth" <kdw### [at] gmailcom> wrote:

>
> But a problem arose when doing the animated matchmoving: POV-Ray's default
> perspective camera is a 'perfect pin-hole' camera. A 'real' camera is not; its
> lens has spherical aberration...

Oops, what I meant to say was 'barrel distortion' (and 'pincushion distortion'
and etc.) Spherical aberration is different, a lack of perfect focus of
different wavelengths of light. My Canon camera shows very little of that.

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> "Kenneth" <kdw### [at] gmailcom> wrote:
>
>>
>> But a problem arose when doing the animated matchmoving: POV-Ray's
>> default perspective camera is a 'perfect pin-hole' camera. A 'real'
>> camera is not; its lens has spherical aberration...
>
> Oops, what I meant to say was 'barrel distortion' (and 'pincushion
> distortion' and etc.) Spherical aberration is different, a lack of
> perfect focus of different wavelengths of light. My Canon camera
> shows very little of that.
>

   That looks like a new usage-case for the meshcam... if you can make a
mesh that gives the same barrel distortion as your real camera.

--
Jaime

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