who has read SCEA's tutorial on SH lighting?

[shuipi]

Here's the address:
http://www.research.scea.com/gdc2003/spherical-harmonic-lighting.pdf

I have a question about the picture on page 13. According to equation 6 on page 11, when both m & l are 0, Y should be K00 * cos(theta), so the value of Y is dependent on theta, since K00 isn't 0. Then why does it say on page 14 the first band is just a constant value?

 

[mmp]

Here's the address:
http://www.research.scea.com/gdc2003/spherical-harmonic-lighting.pdf

I have a question about the picture on page 13. According to equation 6 on page 11, when both m & l are 0, Y should be K00 * cos(theta), so the value of Y is dependent on theta, since K00 isn't 0. Then why does it say on page 14 the first band is just a constant value?

Here's why it ends up being a constant value: for the m=0 case in equation 6, there, you have

y_0,0(theta, phi) = K_0,0 P_0,0(cos theta)

But P_0,0(x) = 1. i.e. it doesn't depend on x, so the cos theta parameter to it doesn't matter, and thus the first band is just the constant K_0,0...

Hope this helps.

-matt

 

[shuipi]

Thanks. I think somehow I took P(cos theta) as P * cos theta