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View Full Version : Grey Styrofoam ball or HDR Shop's 'Diffuse/Specular Convolution'?


Varinder
03-10-2006, 04:05 AM
I read that you don't need to use a grey styrofoam ball to capture the lighting when using HDRI's when integrating a cg element into a live action shot. Because you can simply take your HDRI you just created go into HDR Shop and just use the Image>Panorama>Diffuse/Specular Convolution. And you'll have a spherical 'diffuse' image of your HDRI, similiar to what you'd get with a styrofoam ball.

Is this method better than actually using a styrofoam ball?

monovich
03-10-2006, 05:58 PM
I'd love to know the answer, too.

I never quite understood the specular convolution function, or why it takes so long to calculate.

gerardo
03-11-2006, 06:40 AM
That's depends of how you will use the white/grey ball. I commonly just use it as reference to match my HDRI lighting (acquired from a mirrored ball); but if you want to use it as environment map (diffuse/"specular"(reflection), then yes, you can use the Diffuse/Specular Convolution function of HDRShop, since that's what this function tries to represent, the intensity in that an incident lighting affects a surface according to the cosine of its angle in relation with surface normals, basically this means that if for example we are lighting an object frontly, the top and bottom of this object would receive less light, so you can figure out why this function takes so much time to be calculated. To speed up the things is better if we use use low res images. This Diffuse/Specular Convolution trick is use it commonly to get real time reflections and HDRI illumination "look" (just radiance effect). Specular convolution works great for reflections but diffuse convolution may be inaccurate for more complex models, so be careful with "hero" objects.
Btw, probably you may want to try FakeIrradianceIllumination (by ASA) (http://www.lw-in.org/plugins/asa/fii/plug_fii.html) to apply your diffuse convolution map as an integration map :)



Gerardo

Varinder
03-11-2006, 08:23 AM
Gerardo my hero :D I figured using that Diffuse/Specular Convolution wouldn't repace using an actual grey styrofoam ball. Well, depending on your purposes, but for me, it won't work. Thanks for the info man.

gerardo
03-11-2006, 09:06 AM
maybe it works. but consider this "inaccuracy" on complex models is the same for the styrofoam ball as well. I'd prefer the Diffuse/Specular Convolution instead. You may want to try FakeIrradianceIllumination in conjunction with an ambient occlusion map (SG_AmbOcc), most of the times we can get a similar BackdropRadiosity "look". If you mix it with bounce lights or gradients you can complete the GI effect. Btw, the link above doesn't work, this is the correct link: http://www.lw-fin.org/plugins/asa/fii/plug_fii.html



Gerardo

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