Spherical rendering idea

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Spherical rendering idea

Postby baltort » Wed Nov 01, 2017 9:17 am

baltort Wed Nov 01, 2017 9:17 am
I've been doing lots of spherical rendering for panoramas recently.

For a full spherical panorama we would render 360 degrees horizontal field of view and 180 degrees vertical field of view. I believe Octane is rendering these at a fixed number of samples per pixel. However, I think these pixels do not have an even contribution once the image is remapped onto a sphere.

For example, rendering at 1,000x500 pixels would mean rendering 500,000 individual pixels. If we consider this as a sphere with circumference 1000px, then we get a radius of 1000/(2 x Pi) = 159 pixels. This implies a spherical area of 159^2 x Pi = 79,577 square pixels. This is surprisingly only 18% of the area we are actually rendering. The worst case are the poles; the top and bottom row of the rendered panorama are 1,000 pixels wide but correspond to a single pixel in the sphere.

I wonder if it's possible to take this into account by lowering the number of samples per pixel vertically across the image? Each row of pixels in the render corresponds to a circle of latitude on the sphere, with each circle getting progressively smaller as we approach the poles. If we dropped the sampling rate in proportion to the circumference of this circle vs the circumference of the equator then we would still get even image quality over the sphere but would only need 18% of the total samples. I think that would be 5 times faster...

In summary, is it possible to change the samples per pixel across an image?

Cheers,

James.
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