primary QMC ala PPT based on secondary LC - an idea

[Micha]

Hallo,

I like the combination of LC+QMC. It produce images in high quality within a good rendertime. Often I use the universal method, but I don't like set a fixed noise level. I would wish, we could get a mix of LC and PPT. The process could be: first a LC is calculated and than the final pass would refine the image ala PPT without predefined limit. Maybe we could call it PPT QMC mode.

Often if I use LC+QMC I think, I could render a little bit longer to get less noise, but to start again with new noise threshold is not a good solution, because I lost the previous calculation time. Or I set a to fine noise threshold and during the rendering I see, I have not enough time to finish my render within my deadline.

And now ... with a trick this method can be tested immediately with a restrictions: the continious preview is not working.
(1) render a light cache for a scene and save it
(2) set read light cache
(3) set primary engine QMC and universal settings with very low noise level
(4) set bucket size at full image size - Attention: dual core user must set the bucket at half images size
(5) start render
(6) stop the rendering if you like

The disadvantage of the pure PPT is, that infinte bounce are used, primary and secondary engine are not independent. My idea is, to limit the secondary part with the LC calculation and let run the primary engine in "PPT" mode only.

Now I'm curious for the answers.

This christmas present - I will call it progressiv QMC (PQMC).

-Micha
progressiv QMC - one of two core processor

progressiv QMC - one of two core processor

progressiv QMC - both processors used


standard PPT


My previous PQMC tests has enabled "use for glossy rays" at the LC. Here at test with correct raytraced reflections (good to see at the table-leg). Again, better than the standard PPT.


If somebody like to test it - here my PQMC settings:

[studioDIM]

Re: primary PPT based on secondary LC - an idea

The disadvantage of the pure PPT is, that infinte bounce are used, primary and secondary engine are not independent.

I'm not sure i understand what you are proposing here, to be honest, so i'll just limit myself at the exposure of some facts:

I think i read somewhere that LC is akin a photon mapping with 100 bounces (hardcoded).
LC does calculate both primaries and secondaries, however it's used, anyways (hence the ability to use it for glossies or direct light storage).
So darkening the materials, or lowering the secondary multiplier would already cut the path tracing before the hundredth bounce, speeding up the rendering.
Supposing ppt works the same, a dark material with proper exposure makes the rendering a lot quicker, cleaner and manageable...
And ppt renders can be "resumed" at will.
One just has to use the external merging utility Vlado provided, and render different frames of a "fake" animation with "time independent" unchecked, so to vary the noise pattern and allow proper interference between different frames, to achieve a cleaner final render.

Lele

[Micha]

Lowering the LC multiplier would cause a wrong light distributation. So it is no way. The advantage of the LC is, that after a short time the lighting of a room is calculated (black dots are gone). If you let it render longer, the image will not be brighter. So, the LC give the basic for the lighting.

QMC - I don't like to set a fixed noise threshold. I would like to see a continious refinement of the image. The primary QMC works for primary bounce only, so we could get a speed enhancement compared to the full PPT.

EDIT: extra advantage of this method - no limit of the rays per pixel like with PPT. I suppose, this method could render endless.

[Micha]

... PPT vs. PQMC images added.

[Micha]

Vlado, could you make, that bucktets are updated with the current calculation every minute or so? So, this would be the simpliest change to get this PQMC method full working.

[ene.xis]

i don t see this having anything to do with bucket sizes?

won t u get the same result with a regular 64x64 size?

[Micha]

"Progressiv" QMC means, that you can let render the whole image and stop it every time you like and you get an image with an constant noise level based on the QMC method. Good results I get with noisethreshold 0 and full adaptive QMC 1/100.

If you use a smaller bucket size than your image size and you stop the render process, than a part of your image is rendered only. My PQMC method bring together the advantages of PPT and QMC.

[rivoli]

If you use a smaller bucket size than your image size and you stop the render process, than a part of your image is rendered only.

I'm not sure I'm following what you propose, but I guess that if you stop the rendering half way, even with your method, you'd still get only a part of the image rendered.
I don't see how this can be progressive qmc. at the end of the day what you're describing is good old qmc with precalculated lc for secondary bounces, isn't it? no matter how big or small those buckets are.

[ene.xis]

i don t see this having anything to do with bucket sizes?

won t u get the same result with a regular 64x64 size?

yeah...i see what u mean...
i prove myself wrong just before lunch!
its interesting...but the rendertimes seem huge to get a decent result...

[Micha]

You are right, render times are long. My comparsion is PPT vs. PQMC only. Also I hope, this method is an inspiration to find more shortcuts for easy to use progressiv rendering.
Did you mean the PPT should be faster? Maybe the Vray for Rhino incarnation does something wrong. I would like to find the problem.

[ene.xis]

nop...ppt is slower id guess...
i ll try to run some tests...
yeahh....some multi rendering shortcut might work ...but id stick to standard qmc+LC!

[rivoli]

but id stick to standard qmc+LC!

I must have lost something along the way, how this is different from standard qmc+lc? apart from the bucket size and the increased amount of memory needed for rendering with two of such size?

[travistlo]

I think they want the QMC to work similar to PPT. Where it will keep refining the solution with out having to stop the render and increase the settings.

[Micha]

nop...ppt is slower id guess...
i ll try to run some tests...
yeahh....some multi rendering shortcut might work ...but id stick to standard qmc+LC!

So we use the same method, but my method could rendered without to predeterminate the noisethreshold. Only I need an update of the preview every few minutes. The predeterminated noisethreshold is an disadvantage: if you set a fine noise, you could misss your deadline, if you set a raw noise you lost quality. The PQMC could help to get the maximum quality by this method in a limited time frame.
Example: the scene setup is ready and I think, I could let render the scene over night. Which noisethreshold should I use?

[ene.xis]

I must have lost something along the way, how this is different from standard qmc+lc? apart from the bucket size and the increased amount of memory needed for rendering with two of such size?

micha pointed out that if u use qmc+Lc with ur bucket(s) of the size of the image ull be using this gi solution in a ppt similar way...as one can stop at any time...but u have no preview(!) and yes it must use alot memory...

but it ...erm... works!