[Radiance-general] .pic precision

[Richard Murray]

> Date: Thu, 24 Feb 2005 19:03:12 -0800
> From: Gregory J. Ward <gregoryjward at gmail.com>
> Subject: Re: [Radiance-general] .pic precision
> To: Radiance general discussion <radiance-general at radiance-online.org>
>
> Hi Richard,
>
> As long as you are not relying on textures that derive from images of
> any kind, there is no inherent limitation in the precision of the
> lighting calculations in Radiance -- everything is carried out in
> double-precision floating point.  However, the accuracy of any Monte
> Carlo calculation is going to depend on a lot of different factors,
> such as number of samples and so on, and if you don't pass the output
> to pfilt to filter the result, you are likely to have samples with
> occassional large discrepancies to their neighboring pixels.
>
> Avoiding these variances requires turning off Monte Carlo sampling as
> much as possible, which probably requires no diffuse interreflection
> and only purely specular (polished) or diffuse surfaces.  I can give
> you hints on how to do this if that is what you are after.

Yes, that would be very helpful, thanks.

> To get out a floating-point image without going into the 32-bit/pixel
> RGBE representation, you can use rtrace instead of rpict, like so:
>
> % vwrays -vf view.vf -x 1024 -y 1024 -ff | rtrace -ff -h [options]
> octree > picture.flt

Exactly what I'm looking for.  Thanks so much.

Richard

> This will produce a raw floating-point image with 96-bits/pixel (RGB
> floats in scanline order).  The size of the image can be determined by
> running "vwrays -vf view.xf -x 1024 -y 1024 -d" as it won't be
> 1024x1024 unless you give it a square view, as vwrays produces square
> pixels by default.
>
> -Greg