# -ar parameters

I'm trying to understand the -ar parameters
I'm thinking thats what behind the artifacts in between the couch cushions
in this image
Unfortunately, I don't have the actual -ar value used with me now (I'm at
work) -- I used a rif with high quality, so I'm thinking it was around 93

-ar minimum value is 8, fast is 32 and accurate is 128, yet maximum is 0. So
if I want better quality than 128, can I go to 256, 512, etc or is 0 the
value I should use?

Or is that max 128 only in Deskrad?

Hi Rob,

Seems that no one answered this query, either...

The -ar parameter is a bit tricky, as it's proper setting requires knowing the ratio between the scene octree size (which you can get from the octree with getinfo -d) and the smallest important details, which only the scene author knows. Divide the former by the latter, and this will give you a reasonable value for -ar. For example, if "getinfo -d scene.oct" gives you:

scene.oct: -123.8831 -.00315 -202.67102 431.0032

then the last number (431.0032) is your scene cube size. Dividing this number by the thickness of one of your cushions, say 3.75, you get about 115, which is what you should set for -ar.

Setting -ar 0 sometimes helps but usually does not. In your scene, I think increasing -ad would also help, and this is almost always a good idea when you are seeing artifacts in the indirect calculation. Increase -ad first, then -as, then try increasing -ar, finally decrease -aa. This is the order I do things in, and you can usually find a good place for these settings with a little experimentation. If you don't like waiting for each run to finish, try rendering a lower resolution image of just the problem area in your scene, like the seat cushions in yours.

-Greg

···

From: "Fitzsimmons, Rob" <Rob.Fitzsimmons@Summit.Fiserv.com>
Date: Wed Sep 3, 2003 10:55:43 AM US/Pacific

I'm trying to understand the -ar parameters
I'm thinking thats what behind the artifacts in between the couch cushions
in this image
Unfortunately, I don't have the actual -ar value used with me now (I'm at
work) -- I used a rif with high quality, so I'm thinking it was around 93

-ar minimum value is 8, fast is 32 and accurate is 128, yet maximum is 0. So
if I want better quality than 128, can I go to 256, 512, etc or is 0 the
value I should use?

Or is that max 128 only in Deskrad?

From the Radiance manpages, rpict -ar
Error will start to increase on surfaces spaced closer than the
scene size divided by the ambient resolution. The maximum ambient value
density is the scene
size times the ambient accuracy (see the -aa option below) divided by the
ambient resolution.

This seems to imply you can set it higher than 128, and also decrease the
-aa

thanks

rob fitz