This is the WIP tutorial for backlighting your scenes with an HDRI type image. Unfortunately bryce is stuck rendering my monthly challenge image :) so I can't post any screen shots for you. The tutorial is complete content-wise, but for now it's just my aweful photoshop blueprint disaster.

Intro-
Up till now we have only been able to envelop our scenes in Globes with a special image applied to them in order to simulate an hdri effect. This means unless we want to do a top view still life, we are stuck with our chosen image as the background for our scene. Well now we can do whatever the heck we want as the background for our scenes but still have the hdri reflections!!! Sit back and read on...it's all smoke and mirrors.

Method-
Here's the principle behind this. Let's say we are holding a small mirror in front of our eyes in our living rooms. We can see everything behind us in the mirror, even though we can't see it directly with our eyes. Now imagine if everything in front of you faded away and you were standing on an imaginary line between what was behind you and nothing in front of you. Now if you looked in the mirror again you'd STILL see what was behind you exactly as it looked before. Now imagine our current HDRI simulation setup. We currently have a hollow sphere. This is similar to our world. But now if we punch a hole through the front where our vision is then we can see out of the globe yet still have the reflection behind us!

Here's how to do it:
Create a sphere.
Stretch it along the z axis so it looks oblong, like an american football.(for you brits out there)
Go into the object attributes and set it to positive.
Duplicate the sphere and set it to negative.
Make it a bit smaller in all dimensions and position it right in the middle of the first sphere. To do this exactly, select both spheres, and enter zero for all the position values in the object attributes.
Stretch the smaller sphere along the z axis so it pokes out of the larger sphere a bit.
Group the two spheres.
Make the group much larger.
Shift/rotate until the "hole" is facing the same way the camera is looking.
Move the group over the camera so that the camera is looking out the hole from toward the back of the group.
Make sure the group is centered vertically.
Switch views to camera mode and render. If you see any corners in your image, make the group bigger and sink the camera in more. If you see none, shrink it and move it forward until you do see them, then back up to where you dont. You want to get the camera's field of view in line with the hole in the grouped spheres.
Apply your HDRI type image to the sphere group.
Disable cast shadows for that group.
Do a test render with a reflective object and see how it looks. You should see the default bryce scene before you and the hdri type image reflected in the object.

Here's my aweful photoshop rendition...

Nice tutorial Madmax! Guess placing a blue screen 2D flat (along the dashed line?) might help composite the image! For HDRI works only on reflective surfaces! But how will the rest of the image be lit (say we'd like a Modelled Background as against the HDRI)? So I guess two renders will have to be done! One for normal lighting and the rest of the mats and another with just those objects having highly reflective surfaces with the HDRI applied! I also have a question. Say its a curved surface (a sphere), and we are using wide angle lens? How do we ensure that the white is not reflected onto portions of the object? Second how do we ensure that the spheres intersect right along the line of the camera FOV? The bryce camera FOV reference is only up to a distance and thus this could be used only on small objects which are near the camera. For large objects this wouldn't apply as the object would then have to be shrunk the natural lens distortion would be lost! I think, using the sphere with a matteable color (say RGB Blue or green and the object set to a non reflective contra color, say black, and a second render taken which would result in a matte!

No this method allows for only one render. Because you disable the cast shadows for the large sphere group, the sun will act normally. When you apply the HDRI image ti it, click the button for ambience as bot ambient channels in the mat lab, and nothing else. No diffusion or anything. This will ensure that the image is always exactly as bright as is supposed to be, and it won't be effected by other scene lights. To get the FOV aligned, it's just trial and error adjustments until I can post the actual specs. What do you mean by "only up to a distance?" You just have to align the camera's sight path with the edge of the hole. If you do this right, it works fine for spheres, because the spheres are behind the edge enough that they have the correct reflections. As I said I am sorry I can;t show a more complete tutorial yet. I assure you when it's done it will be easier to see. Check my next post for an example image.

Here's an example image although you can;t see it, the 2 spheres group is right at the corner's of the camera's FOV. If I wanted to make the sphere group way bigger to surround a bigger scene, I would set the origin handle of the object (attributes/show origin handle) right to where the camera's "eye" would be. Now when I resize it, it will always be outside of the camera's FOV. You can also experiment with weirder boolean arrangments, for example, one huge flat sphere spanning way out to the sided of the camera, stuff like that. I will try a few once bryce is freed up.

Hmm, could be a lot of fun doing this. EIU does HDRI pretty well. I've used images on a 2d plain behind the camera, never thought about the open sphere thingie. Great idea. Gonna have some fun with this I think. Thanks.

Can someone define "HDRI" please.

HDRI stands for High-dynamic-range-image. This means that HDRIs contain more information than a normal color photo, such as how to behave under low-light environments, or bright environments or how to control contrast. Bryce can't use these images, but we refer to global reflection images as HDRIs...just because it stuck with us.