# volume rendering

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http://http.developer.nvidia.com/GPUGems/gpugems_ch39.html In section 39.4.3 Rendering, the above book has: "The assigned opacity also depends on the sampling rate. For example, when using fewer slices, the opacity has to be scaled up, so that the overall intensity of the image remains the same. Equation 3 is used for correcting the transfer function opacity whenever the user changes the sampling rate s from the reference sampling rate s0:" (*) A = 1 - (1 - A0)^(s0/s) My question is, how does one determine the reference sampling rate s0? That is, given a volume, how does one decide what s0 should be? Or does it work like this: I pick an s0 experimentally that satisfied the Nyquist theorem, then define a transfer function based on that s0. Then if I later want to change the sampling rate, I apply (*), which should closely match the opacity when using s0?

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Quote:
 Original post by QuatOr does it work like this: I pick an s0 experimentally that satisfied the Nyquist theorem, then define a transfer function based on that s0. Then if I later want to change the sampling rate, I apply (*), which should closely match the opacity when using s0?

Yep, that's baically it. You choose a suitable sample distance and create a transfer function which works well for the sample distance you have chosen. Then, if you change the sample distance (e.g. for high speed preview renders) then you can adjust the opacity as shown.

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