RE: Unwrapping chrome ball pictures...

[Joe Laffey <joe(at)laffey.tv>]

On Tue, 30 May 2006, Martin Belleau wrote:

> I figure that an actual 12-bit RAW image is a lot better than a Chrome ball
> reflection... Since we can now get the "almost" same effect from an extreme
> fish eye lens as a Chrome ball, without getting the tripod or camera or
> person shooting in the frame... sounds to me like a great trade off.

Good point. It would be sharper. But as far as the bit-depth goes, I 
assume you are shooting the full bracket (I usually use 1/8000th down 
to 1 sec in single stop increments for outdoors) and combining them into 
one HDR image, right?

> Also I
> noticed that you can't get the complete 180 with a chrome ball. (unless
> someone knows something that I don't).

In order to get all of it you shoot the ball twice, 90 degree opposed. 
Then you combined the two images. See this article:

http://gl.ict.usc.edu/HDRShop/tutorial/tutorial5.html

Note that I use a 10 inch gazing ball, which seems to provide much higher 
resolution then those little chrome balls.

Note, however, that if you are using the ball for lighting (and not 
reflections) then you want a low-res image anyway (like 512pixel or so). 
High-res IBL can lead to more noise.


> As for why I'm getting into all of this, its because we have vray here at
> work, and it brings a tear to my eye. It does things with light that I seem
> to have a real hard time doing in XSI. First off, the fact that I can't use
> objects as light sources severely puts me at a disadvantage. I've been
> spending my days in the parking lot taking pictures and looking at how
> reflections work with base colors. 100% reflective balls, XSI can do, but
> when it comes to 20% reflections, I can't seem to get that "real" feel to it
> like vray does. Final Gathering is okay for outside shots, but for indoor
> shots, the light bouncing just doesn't work like it should. I've even tried
> going up to 50+ bounces and I can never achieve what vray does automatically
> without effort.


20% reflective balls should be relatively straightforward in most 3d apps. 
Now I have not messed with vRay, but my background is large format 
photography (originally). Are you remembering to lower your diffuse value 
when you increase your reflectivity? Also, be sure your ambient is 0% for 
max contrast.

> All of the above is why I'm trying to figure things out... I like the chrome
> ball, and I want to see if its really the only real way of getting the
> maximum out of HDR images.
>
> Anyhoo... any thoughts for the above I'd appreciate tips and tricks.

PS can combine the images for you, which is easier than using HDRShop. It 
can also account for camera movement (misregistration) between the 
bracketed shots.

PS can clone in floating point mode. So I usually clean up my balls in PS 
(that sounded bad). Though I have also done it in Fusion, which lets you 
do almost anything in floating point.

--
Joe Laffey                |       Visual Effects for Film and Video
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