Is HDRI Raisosity?

No, it is not.

http://en.wikipedia.org/wiki/HDRI
http://www.debevec.org/ReflectionMapping

Hi ronviers,

radiosity (more general known as "Global Illusion" - GI) means that all the light in an image is used to lighten the objects in View. That means, that also the objects, that surrounds an Object in focus lighten up this object by indirect light and influencing the color of the light by their own color.

Modern 3D-Render-Engines use different kind of algorithms to perform that global illusion. But you can use GI and HDRI together which gives very realistic looking renderings but costs quite a lot of rendertime.

The Thing about HDRI is, that these images contain more detailled light information than normal jpg-Pictures do. Normally jpg-Pics use 8 bit per color-channel, hdri-images contain up to 32bits of information per channel.
In reality the sunlight is much more brighter than a jpg could take and the relation between the brightest spots to the darkest is restricted to 256 steps (Lab-Channel).
HDRI-Images cannot be viewn by any display or monitor due to its very large brightness range.
But the information in an hdri can be used by renderengines to create these realistic renderings.

regards, Rilos

Well, HDR is a channel format, which allows us to express light values with increased precision and range, which is enough not only for display, but also for next-to-lossless processing. The major shift is not from 8 to 32-bit (there are 16-bit HDR formats), but the shift from integer to floating point, which adapts very well to the imaging needs, providing required precision in the 0-1 range which is considered the unadjusted vision limits and providing required range above 1 range, allowing us to express the notion of "very very bright" objects, which are subject to human vision exposure adaptation.

On the accuracy of percieved tone representation -- while HDR itself as a format greatly improves the realism of the images (also allowing us to simulate vision adaptation without faking glow or bloom), it has nothing to do with properly representing tones -- it is a task for color model along with color management system. Also, I consider 32-bit RGB HDR images to be enough for current needs, since we still have inferior (often unadjusted and uncalibrated) display hardware.

To conclude: real power of HDR lies in preserving more information from original environment it was created from (or synthesized with programs like Filter Forge), to allow further processing simulating human vision exposure adaptation phenomena on common displays.

Can I just say that some of the acronyms used in this thread are incorrect...

GI - Global Illumination

HDRI - High Dynamic Range Imaging

and 'readiosity' is actually Radiosity