[Radiance-general] Fw: How to increase the rendering speed?

[Greg Ward]

Hi Huang,

Just in general, I prefer that people not post images in their  
messages to the mailing list, but you did, so I am, too...

The attached plot shows the correct Fresnel behavior for smooth  
dielectric surfaces, including plastics, waxed floors, and just about  
anything else with a specular reflection.  Radiance 3.6 uses an  
approximation to Fresnel reflection that is fairly accurate down to  
an index of refraction of 1.35 or so (water), but this was left out  
of the version that became Desktop Radiance due to normalization  
concerns I have since resolved.

The problem in your case is that you have specified a material that  
doesn't make sense, physically -- a perfectly smooth (zero roughness)  
floor with a specular reflection of 0.004.  I challenge you to find  
such a surface in the real world -- this corresponds to an index of  
refraction of about 1.135, which is greater than any of the gasses  
but less than any liquid at room temperature.  (Check out the web  
page <http://www.luxpop.com/#index%20of%20refraction%A0> if you want  
to know some physical ranges.)

Be that as it may, Radiance should really disable this approximation  
when the specularity is below the values for which it is accurate,  
which is around 1.8% (n=1.31).  I will fix this in the next release.   
In the meantime, you can set a roughness value of 0.01 or so to  
eliminate the problem in your model, as Radiance already disables the  
Fresnel approximation for rough surfaces, even when the roughness is  
very small.

As for the subject of your message, the best way to speed up your  
rendering is to increase the -aa value while setting the AMBFILE=  
variable in your rad input file.

-Greg

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> From: "Huangwx" <ap.huangwx at archi.kyoto-u.ac.jp>
> Date: December 7, 2005 11:33:55 PM PST
>
> I do not know why the server deleted the text part of my letter.  
> here is the letter.
> Dear all:
>
> I am trying to render an interior scene in daytime and nighttime. I  
> would like to render many images with different material colors and  
> textures in this scene, that means the geometry and illumination  
> remain the same, but the materials on the wall, ceiling ,floor and  
> so on change. The image size I need is very small(175*255 pixels).  
> I need to render the images as faster as possible. So I wonder is  
> there any way to increase the rendering speed?
>
> I am using the Desktop Radiance2.0, I found it renders my model  
> much faster than the Radiance 3.6 in cygwin. (2 min vs. 12 min. on  
> same computer), and the results are different, the floor rendered  
> by Radiance 3.6 in cygwin seems too much reflective. Are there any  
> differences in the default settings of them? or is there something  
> wrong with my installation? (Actually I just copy the model to  
> cygwin directory and inpute the command: $ ./day.bat )
>
> You can find my model here:
> http://munemoto-lab.archi.kyoto-u.ac.jp/storage/huang/12.7.rar
>
> I think it may be not easy to answer these questions, but your  
> reply will be great help for me.
>
> Yours,
> Huang
>