Using Debevec Skyprobes

[davedjohnson]

I'm interested in using the hdr skyprobes that Paul Debevec has on his website to do some testing. I can read the images without any trouble with mplay, but the arrangement of them seems like it would be complicated to use as a reflection map or projection map with global illumination.

It says they are angle maps, which to my eye looks like they are just the regular image that you would get when photographing a gazing ball.

My next step would be to go and shoot my own images, but the projection still seems to stump my mind.

Does anyone have any suggestions on how to project the mirror ball into a reflection map?

Dave

[Jason]

If you download HDRShop from Debevec's site, I believe it supports some panoramic transformations from Angle/MirrorBall to LatLong.

[davedjohnson]

Yeah, well not to start any OS wars, that requires using Windows. Using HDRShop is not enough reason for me to add a Windows machine to our pipeline/shop/existence. I was hoping that someone might have a clever algorithm or Linux/Mac based solution. Maybe I'll find a friend who has a Windows machine to try it out on and figure out how to do the transformations myself. If I do, of course, I'll share here.

Dave

[crunch]

Yeah, well not to start any OS wars, that requires using Windows. Using HDRShop is not enough reason for me to add a Windows machine to our pipeline/shop/existence. I was hoping that someone might have a clever algorithm or Linux/Mac based solution. Maybe I'll find a friend who has a Windows machine to try it out on and figure out how to do the transformations myself. If I do, of course, I'll share here.

Dave

23567[/snapback]

isixpack has a mode which reads the cross style images to create an environment map. Run "isixpack" to see the help.

[Mario Marengo]

Hey Dave,

If you want to map a probe directly to latlong, then you can use the projection that they give you in Debevec's site. They provide you with spherical<->probe, so all you need is latlong<->spherical (with the spherical projection as the common space).

Here's a quick'n'dirty implementation as a VOP COP:

Probe2Latlong.zip

I wanted to preserve the VOP network so you could see/modify it, that's why it's a cpio file.

To load it into houdini, open up the textport and type:

/ -> opcf /vex
/vex -> opread Probe2Latlong.cpio

Then go into COPs and add a "Probe2LatLong" COP. Override the image size to something like 1000x500 (or anything that's twice as wide as it is high) and point it to one of debevec's probe files (not the envcube crosses, but the actual probe images). You should see a panoramic (latlong) version of it in the viewport.

<edit> Also remember to change the bit depth to 32-bit float, or half </edit>

Please note that this is a *very* simple implementation of the projection math. It doesn't deal with any kind of filtering at all (although if you're using these for diffuse illumination then it probably doesn't matter since you'll likely end up blurring the heck out of it anyway ).

If you need better quality, you should do stochastic sampling over the source quad -- meaning that you should project not just XY, but rather [XY,XY+dX,XY+dY,XY+dX+dY] and pass all four to the colormap() function (along with the number of samples). I would have done it except it's late and I don't feel like doing that kind of thing in VOPs (the projection should be its own function, etc, etc)...

Anywhoo... hope that helps get you started at least.

Cheers!

[Marc]

We actually have the preconverted, rat-ified versions here on odforce :

rats

Just for a quick fix if you need it .

M

[Mario Marengo]

We actually have the preconverted, rat-ified versions here on odforce :

rats

23808[/snapback]

Yup, those are definitely useful to have, but I think he's planning to shoot his own probes, in which case you need some way to go from the probe's projection to one of the standard environment projections (latlong or cube).

The little VOP-COP I posted does the probe-to-latlong mapping (w/o filtering).

[Marc]

I'm interested in using the hdr skyprobes that Paul Debevec has on his website to do some testing.

23527[/snapback]

I was responding to this part ... they're good for testing.