View Full Version : Custom MR Shader {photon inquire}

06 June 2003, 06:29 AM
Hey hows it going :D Im in the process of trying to figure out how to set a photons maximum illumination for a surface. For instance sometimes a high energy setting is needed to light objects that are 2 to 3 photon bounces from the original striking surfaces. Sometimes this can cause a very high value on surface hit one. Of course you could turn down the settings on that particular object. But now it can cause your first bounce object to be underlit in the gi pass.

An easy way for what I guess im trying to get at is a min and max setting if at all possible. Saying the photon cannot illuminate over a specified value.

If anyones had some expeirience with this sort of subject any feed back would be welcome :D

06 June 2003, 08:12 AM
For stills, one way to get around this would be to let the illum value get as high as it wan'ts to, as long as the dimmest parts are lit the way you wan't. Then save the render in one of the HDR formats like .map or .ct with float values (in the render options) Now you can open the render in something like HDRShop, and use the exposure controls or a plugin like 'tonemap' to compress the HDR to LDR.

You will of course have to convert the map/ct files to .hdr format using the imf_copy tool

07 July 2003, 08:45 PM
I don't know that answer to your question, but if I can offer a workaround to the problem, that would be to experiment with light exponents that are between 1 and 2.

At 1, too much energy is sent back to the scene by the surface after a hit. The GI model is supposed to work with realistic parameters, wich means that the light should fall off at an inverse square rate. At 1, the falloff is linear, so too much energy gets propagated in the scene.

At 2, the light falls off at an inverse square rate. This is much more realistic, but in complex scenes you may need more bounces or to crank up the intensity (wich results in burning areas near the source) to get light everywhere).

So a value in-between might do the trick.


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