[Bf-cycles] Mirror ball crop

Brecht Van Lommel brechtvanlommel at pandora.be
Thu Jun 21 15:11:46 CEST 2012

In principle it's of course possible to do this. There exist circle
detection algorithms if this needs to be automatic, but that needs
quite a bit of coding time. Or it could perhaps be done more manually
by keyframing a mask in the tracker, but then I guess still missing is
some automatic way to crop the image to the bounds of the mask, which
is not particularly hard to implement.


On Thu, Jun 21, 2012 at 12:45 PM, Tony Mullen <tony.mullen at gmail.com> wrote:
> Hi Dalai,
> Thanks for the feedback.
>> Have you considered capturing it with a fisheye instead or a mirrorball?
> Well, the first bottleneck is budget. I have a DP with a Red Epic, but
> he doesn't have a fisheye lens for it. I can look into buying him one,
> but it might be a bit costly for me.
> The second thing is that what I had in mind was to shoot ordinary,
> undistorted movie footage using the mirror ball to stand in for the CG
> object, and then crop that mirror ball out and use it as a
> light/reflection source, then composite the CG object back into the
> original movie footage. This way, all the live action stuff would be
> shot once, and the reflections would be automatically captured on the
> surface of the mirror ball.
> Basically something along the lines of this:
> http://www.hdrv.org/IBL.php
>> Either way I think you will have a better luck by pre-processing the input
>> into any of the standard inputs that blender can take. Or the processing
>> time is your bottleneck?
> I imagine it shouldn't be hard to export the HDR video to a sequence
> of .hdr still images (I'm not 100 percent how to do this in Redcine,
> but I guess it can be done). The tricky part is cropping it to fit the
> Cycles mirror-ball mapping requirements. I guess there are probably
> tools somewhere that can be used for batch cropping HDR video frames,
> but I'm not sure how to do that. If it could be done in Blender it
> would be pretty handy, I think.
> Keyframing the crop was just an idea I had to make the setup more
> flexible. I think it could be pretty powerful. Basically a silver ball
> anywhere in a live action scene could be cropped out and used as an
> accurate light source, even if it moved around within the shot.
> T
>>> Hi all,
>>> I'd love to use HDR video from a Red Epic as a light/reflection
>>> source. It seems like the best way to do this would be to use an HDR
>>> video of a mirror ball, and use the mirror ball mapping. It seems like
>>> it would be quite helpful to be able to crop the image from within
>>> Blender. For example, to place and scale a circle in the UV Image
>>> editor to tell Cycles what part of the video frame to use as the
>>> mirror ball.
>>> Even cooler would be to be able to keyframe the size and placement of
>>> the cropping circle, so that you could "rotoscope" the position of the
>>> mirror ball within the frame, enabling the camera to move more more
>>> freely (the light source would then be mapped to follow the camera's
>>> movement within the 3D space).
>>> Does this sound like something that can be done, or is anybody
>>> planning to implement something similar?
>>> Regards,
>>> Tony
>>> _______________________________________________
>>> Bf-cycles mailing list
>>> Bf-cycles at blender.org
>>> http://lists.blender.org/mailman/listinfo/bf-cycles
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