Winterclaw opened this issue on Sep 30, 2012 · 29 posts
kalrua posted Tue, 02 October 2012 at 9:29 AM
Quote - Paul Debevec is the Godfather of environment mapping techniques, such as IBL.
He wrote:
Quote - It may be good to downsample the environment image first since the convolution calculations can take quite a long time.
The purpose of that parameter is for you to DOWNsample your image, not keep it high res or, shudder, to up sample it.
http://ict.debevec.org/~debevec/HDRShop/tutorial/tutorial6.html
Quote - Resize the image. Click on Image in the menu bar, then Size from the Image menu then Half Size from the Size menu. Repeat this several times until the image has been resized to a point where HDRshop can calculate the convolution in a reasonable amount if time. In this example the image has been resized to 128x64 and the convolution calculation takes about 96 seconds.
Things are faster now, but he was dealing with 96 seconds!!!!
Most of the pros use 128 or 256 pixel IBL.
http://www.hdrlabs.com/picturenaut/plugins.html
"
Diffuse SH
It's a plug-in which calculates diffuse convolution of an HDRI (panoramic format). It speeds-up complexity to O(n) against O(n^2) of the naive algorithm implemented in HDR Shop 1.0.3. The algorithm is based on the paper "An Efficient Representation for Irradiance Environment Maps" by Ravi Ramamoorthi and Pat Hanrahan of Siggraph 2001. In the example the computational time is less than a second with an 512x256 HDRI, against the six hours expected using the naive algorithm. This plugin creates a ASCII file with the coefficients of Spherical Harmonics calculated"