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View Full Version : How do i use these type of hdri's



Otterman
03-27-2009, 06:55 AM
Ok i feel a little silly asking this but here it goes anyways....

Ive a bunch of hdr images that i use either as a textured environment or image world reflect! I sometimes map these images on illuminos geometry also but these have always been probes or spherical.

How do i use these kind....you know the boxy ones. Dropping it in as textured environment or image world dont cut it and mapping it on a box is a bit of a ball ache. Surely i dont have to UV it?

Is there a simple way for using them ???

Red_Oddity
03-27-2009, 08:41 AM
Download http://www.hdrshop.com/ and use the panoramic tranformation tool to turn it into a langitude/longitude hdr map (or and Angular hdr map) so you can use it in LW.

gerardstrada
03-30-2009, 02:11 PM
If you want to use the cross format precisely by the benefits of its cubic coordinates, then yes, you need an UVmap.

Its benefits for integrating CG elements with live action plates might be justified mainly for 2 reasons:

1. Is a viable format, as other method, to obtain panoramic radiance maps through fisheye lenses; basically the method consists on taking a series of quadratic photographs (north, south, east, west, up, down) to assemble all these images later in a single omnidireccional cubic image.

2. The coordinates of this type of format is represented as straight lines and provides an environment almost free of distortion. This is important because we cannot only use the radiance images to recover the illumination, but the reflactance properties and the geometry of the scene; is due to this last reason than the cubic mapping is very useful too; since for photogrammetry process is easier to calculate the space geometry with this coordinates format, if previously, we've used a camera calibration grid or take note of the size and position of the chrome ball relative to camera and the camera parameters, (this procedure is very useful to determine what parts of the scene should be considered local and which distant); projecting the map onto environment and reconstructing an approximate geometric model of the local scene, as it's necessary.
The straight lines of this coordinates format, also facilitates to retouch the image if you haven't been careful of positioning your camera appropriately, but you've been careful to take several photographs to the chromeball from different directions.

For illumination, Red_Oddity's advice is good, seeing that if you wanted to use this format, you couldn't use Backdrop_Radiosity (although is possible through the spinning light trick and other methods). Some time ago I did design a lightbox rig which makes uses of this format. I explain the setup here:

http://www.spinquad.com/forums/showpost.php?p=162137&postcount=19

Nowadays we can use also the Custom Light from Denis Pontonnier.

I only know very few approaches for calculating irradiance maps based on cube's model for GI solutions, however besides the previous light rig, there are more accurate approaches for spatial IBL rigs whom make use of the 'cross' format.



Gerardo

Otterman
03-31-2009, 05:55 AM
Thanks for heads up Mr R Oddity ll download the app when i get home, looks like its free!

Gerard-wow, thats nearly a textbook...above the call of duty...ta v much!

colkai
03-31-2009, 06:21 AM
Gerard-wow, thats nearly a textbook...above the call of duty...ta v much!

Indeed, trust gerard to impart such wisdom. :) :thumbsup: