do i have to convert hdri maps to rat format as the video tutorial suggests?
Don't have to - hdr can be read and used in mantra directly, however there are indeed advantages to converting to rat - for one thing you can filter the map in the texture call with rats - not so with other formats. Personally I tend to use rats everywhere, although now that exr is here…hmmmm…
but i actually tried to isixpack some vertical cross ones and i got an error
from the isixpack help:
Alternatively, it's possible to take a single image which is laid out in
the shape of a cross (similar to http://www.debevec.org/Probes/) [debevec.org] and
generate a single reflection map (must be a cubic .rat file).
does houdini support openEXR fully now? by that i mean 24 bit.. suitable for hdri substitute… is there an advantage of openEXR over hdri? for everyday use i mean…
Houdini, as of the last few cuts, does support exr completely throughout the pipeline - compositing, mantra, etc. There are four very kewl things about exr:
1. ILM determined through experimentation and real world production that using this “half” format(16 float instead of 32) gives you results that are pretty durned hard to differentiate from pure 32 bit floating point. It's actually significantly *better* than 24 bit - it's floating point. I've been fiddling with it a fair bit the last few days and it's amazing what you can get rendering oexr layers for some fancy comp footwork. I've actually had to watch myself, however, since in the past I might do some sloppy tricks that counted on, say, an alpha channel peaking at “1” and not going any higher. Now there's headroom
, and I had problems down the pipe with the comp. I actually have to be more careful now - assume nothing! However, the freedom you get, the comps you get - just being able to pull brightness by 1/2 and not get that gruesome flat grey…yummy!
2. 16 float = half the size of 32! Quicker to render! Zoom!
3. Lots of other nicieties in the oexr spec, like not just 16 - but the full range of bit depths, mip mapping, scanline, dataWindow/displayWindow(which lets you have an image that is larger than the actually area you are going to see - really handy for compositing down the line), etc. Of course, Houdini doesn't yet support *all* these features(notably the last one), but hopefully…
4. In cahoots with NVidia, the 16 “half” format has some very clever display tricks with high end NVidia cards. I can display an oxer image on my FX3000, and it moves around almost as fast as an 8 bit! Try that wth 32 bit and it will crawl…
So definitely, yes, oexr support is really there - highly useful, and it's fast.