More of a general effects question this but here goes…!

I want to produce a reflection map for some glass. I have taken a chrome ball image to get the map, but do I just use that or do I need to unwrap the spherical reflection on the chrome ball to a 4:3 aspect ratio first?


Cheers

Have you read this? http://www.odforce.net/wiki/index.php/CreatingReflectionMaps [odforce.net]

It might help answer some of your questions…

Thanks…I did have a quick scoot around the net, a lot on reflection mapping but couldn't find anything which answered that particular question…….

Cool…great article but I'm afraid it didn't answer my question. This shows me how to auto-generate a reflection map for a CG environment within Houdini. I would like to know how to use a reflection map taken with a chrome ball when my environment is live action, with CG elements in the foreground…..

Take the chrome ball image and project it on to a sphere and unwrap it.

It'll distort like heck on the edges, but you can clean that up with a bit of photoshop work.

I can't remeber whether reflection mapping uses polar or cylindrical mapping. maybe tinket with that to find out. that way you can make sure you unwrap correctly.

that'll give you a flat image that you can use as a reflection map.
I'mn not sure it matters if it's 4:3. unwrapping it to a square map should be fine.

Search the net for Paul Debevec's HDRShop (I think it's just www.debevec.org) and you'll find ways to transform photographed mirrorballs to lat-long projections and so on.