Can this be explained in terms a semi-luddite artist is able to understand?
...OK that all went by me [makes gesture of hand passing over head].
What - my previous post? Well ...
I'm not an expert at this stuff by any means, but AIUI -
A basic problem with using big HDRI images as the environment maps for Global Illumination, IBL etc is that when you combine the shear amount of data in them and hi-rez detail, you have to use very VERY high quality settings not to get odd artefacts appearing in the render where often abrupt transitions from one detail to another in the environment map affect the lighting in the scene. This means (a) needing a high poweer computer, and (b) humungous render times. (I'm not talking DS specifically here, but all the assorted rendering solutions like Lightwave, Maya and whatnot.)
So the usual solution is to shrink the HDRI image and apply a 'spherical convolutoion' to it - basically blurring the image a lot, but through a specific form of blurring that retains the optical properties of the light. This small, convolved image HDRI image is then used as the environment map for the GI, IBL, IDR. The blurring loses the transitions that cause the artefacts, and as the details have been blurred the size isn't necessary, but you still have the full dynamic range that makes it HDRI. So using the small, convolved map you can use much lower quality settings and get relatively quick results with a much lower power computer.
If you are doing proper ray-traced reflections, though, you do need reasonable detail in the map for that. So as the map for that you want an HDRI image, NOT convolved, but still doesn't need to be as big as what you use e.g. on the skydome as a background. And then you want a really big image for the skydome, but a regular LDR image.
So the general solution, as used with Lightwave, Maya etc, and also with the UberEnvironment products as with the files supplied by Ominfreaker, is that for an environment light set up, you start with a BIG HDRI map, and from it produce:
i) A big LDR JPEG or PNG version to texture the skydome.
2) A smaller HDRI version to use as the environment map for reflections.
3) A very small convolved HDRI version to use as the environment map for GI/IBL.
4) A standard distant light, lined up appropriately with the maps and appropraitely coloured to act as the sun, to give sharp shadows and controllable intensity for the sun light.
If you go to the Smart IBL section of the website I linked above - http://www.hdrlabs.com/sibl/index.html
, then read that Overview page and the How it Works one in that section you'll see this discussed and explained, again noting this is general for all CGI applications, If youi then follow the sIBL archive link, you'll find a page with lots of lighting sets arranged for the sIBL software. Just download one. It's a zip. Open it and you'll ffind a set of files, as discussed above, whch are actually perfectly useable in DS.
I'm looking in the 'desert highway' set at the moment, and in the zip, for that one lighting set are:
An 8000*4000 jpeg (LDR) to use on the skydome.
A 1600*800 hdr to use for reflections
A 360*180 convolved hdr for the environment map for IBL/GI
All created from the one original 8000*4000 hdr, and together making up the set needed for a remder of that setting.
There's also a 600*300 jpg preview, and a 128*128 thumbnail reeady for use packaging for a particular app like DS or whatever, and an .ibl file. If you load the 'ibl file into a text editor, you will see that it's in fact a perfetly readable set of metadata (in the Smart IBL metadata format) which includes the colour (in RGB) and position for a matching sunlight, as a normal distant light of the application being used, like Lightwave, Maya ... or DS.
Note that these image files mare in the correct longlat format used by DS, so all the sets for download on that page are quite usable with DS. All you need to do is run the HDRConverter.dse in the Uberenvironment2 folder in DS on the two .hdr files (the reflection one ending _Ref.hdr and the environment map one ending _Env.hdr) to change them into tiffs, and you have the set of jpgs and tiffs to use with UE2 for the IBL/GI, reflections and skydome.
So you can use the sIBL sets in the archive as examples of what image sets to create for use in DS. And you cna also use them to stock up your library.
Final thing - go to the menu on the right side of those sIBL pages and Click on Software, and in the expanded menu click on sIBL-Edit, Have a read, and then I'd recommend downloading it along with some of the sIBL sets from the archive. Note two things:
1 pick a folder, say in your DS My library runtime Textures and call it sIBL, and unzip the sample sIBL sets into folders in that. Start sIBL-Edit and select that folder with the sIBL sets in in the preferences, and you will find that sIBL-Edit gives a neat interface to look through all the sIBL sets you've donwloaded, see the images and details on them, the sun colours etc. Neat, but even more ...
2 In sIBL, if you click to create a new sIBL set and then choose one large .hdr you've downloaded from somewhere else, sIBL-Edit will, in about 1 second, automatically create from the large .hdr (a) the fullsize jpeg for the skydome (b) an appropraitely reduced size .hdr for the reflection map (c) the appropraitely even smaller AND convolved hdr for the environment map, and (d) even a preview image and thumbnail. As I say, all you do is click to start a new sIBL set, select the source large hdr, and BAM - it makes thee whole set in a second. It offers the set of images made with the default settings, but in a UI so you can, if you want, alter sizes, change which bit is cropped for the thumbnail, apply all sorts of transforms. AND it will convert any HDRI projection to any other. So you can start by selecting a large mirrorball HDRI, then when the images are made, just change the 'projection conversion setting' to mirrorball to longlat and not only do you have the set of versions, bbut they've all been converted to the format DS uses.
Worth having a look, a browse and a play, IMO.