Search found 138 matches

by shiqiu1105
Fri Oct 03, 2014 8:45 am
Forum: General Development
Topic: An error in pbrt? About MLT start-up bias
Replies: 0
Views: 9518

An error in pbrt? About MLT start-up bias

Hi I have been reading the MLT implementation in pbrt and trying to understand the math as much as I can. One thing that confuses me is that, here in the start up phase, the initial sample X0 is sampled in the following way. 1.jpg where it says we need to weight all contributions with w. However, wh...
by shiqiu1105
Thu Oct 02, 2014 11:13 pm
Forum: General Development
Topic: Questions about metroplis sampling.
Replies: 22
Views: 15439

Re: Questions about metroplis sampling.

friedlinguini wrote:
I don't think there is supporting literature. Csaba Kelemen posted that code on his site and also on the original OMPF board, and then seemed to vanish from the rendering world. See also, "Delta Sampling."
Yeah I noticed delta sampling on his website too! Seems really cool.. what a shame..
by shiqiu1105
Thu Oct 02, 2014 9:30 pm
Forum: General Development
Topic: Questions about metroplis sampling.
Replies: 22
Views: 15439

Re: Questions about metroplis sampling.

Just realized that the MLT implementation in pbrt is actually primary sample space..
I always thought it's path space.
Will definitely read it!
by shiqiu1105
Thu Oct 02, 2014 8:53 pm
Forum: General Development
Topic: Questions about metroplis sampling.
Replies: 22
Views: 15439

Re: Questions about metroplis sampling.

Reposting in case nobody noticed this in the last post of the previous page..

Also, does anyone know how the updated metropolis sampling, which requires no warm-up, works?

http://www.hungrycat.hu/MetropolisSampler.html
by shiqiu1105
Thu Oct 02, 2014 6:20 pm
Forum: General Development
Topic: Questions about metroplis sampling.
Replies: 22
Views: 15439

Re: Questions about metroplis sampling.

Also, does anyone know how the updated metropolis sampling, which requires no warm-up, works?

http://www.hungrycat.hu/MetropolisSampler.html
by shiqiu1105
Thu Oct 02, 2014 6:00 pm
Forum: General Development
Topic: Questions about metroplis sampling.
Replies: 22
Views: 15439

Re: Questions about metroplis sampling.

...high quality samples ... On another note, whether MLT really produces higher quality samples is debatable. Sure, the sampling density is proportional to the target function, perfect importance sampling and all that, but it comes at a price. When MLT gets stuck in a peak of the target function fo...
by shiqiu1105
Thu Oct 02, 2014 7:10 am
Forum: General Development
Topic: Questions about metroplis sampling.
Replies: 22
Views: 15439

Re: Questions about metroplis sampling.

That way we get high quality samples AND equal amount of samples per pixel. The point is exactly to not get an equal amount of samples per pixel (aka adaptive sampling): more samples where they are more useful (or better where they are supposed to be more useful). If you are looking for an example ...
by shiqiu1105
Thu Oct 02, 2014 7:07 am
Forum: General Development
Topic: Questions about metroplis sampling.
Replies: 22
Views: 15439

Re: Questions about metroplis sampling.

That way we get high quality samples AND equal amount of samples per pixel. The point is exactly to not get an equal amount of samples per pixel (aka adaptive sampling): more samples where they are more useful (or better where they are supposed to be more useful). If you are looking for an example ...
by shiqiu1105
Thu Oct 02, 2014 3:57 am
Forum: General Development
Topic: Questions about metroplis sampling.
Replies: 22
Views: 15439

Questions about metroplis sampling.

Hi all, Lately I am trying to implement keleman styled metroplis sampling. I just finished reading the paper and, despite the author has provided source code, I am still quite confused. One thing I want to ask is why does it use only one markov chain for the entire image, instead of using one chain ...
by shiqiu1105
Thu Jul 31, 2014 6:08 am
Forum: General Development
Topic: Total SAH of a BVH
Replies: 11
Views: 11624

Re: Total SAH of a BVH

jj99 wrote:I was looking at this code too. Their value seems completely useless IMHO :)... But I mupltiplied the SAH(leaf) by the area of the child box. It seems working. If I remove the bvh rotation, it increases.
So the SAH calculation of embree is wrong?