Progressive / RT takes ages to reach Color Thr on last pixels..

[Subburb]

Hello,
i do like the idea to give a noise thr value for progressive render and RT.
It allows to have a constant quality in minimum time.
BUT !! this method have a real issue imo. When 99% of image have reached the specified noise thr, it accelerate, and takes ages to polish the last pixels...
That's very frustrating...

In this example, (progressive render) i've set a noise thr = 0.01

The image cleans up (very fast) in 50s.
BUT the rendering total is... 5m12s ! With still remaining red circles (they were dots in beginning and starting to grow while rendering).

Do you think a workaround can be possible here ? like abort if 99% of image pixels have reached the noise thr ?

[vlado]

It's definitely something that I want to take a look at.

Best regards,
Vlado

[Subburb]

Hi Vlado, thanks ! nice to know

[Subburb]

ok i've played a bit with progressive and color thr issue and found some intersting things :

Increasing ray bundle size reinforce the problem : more red dots are created (mask dots) at the end of render, then they start to grow and became circles. (inside circles the sampling is clearly "too much").
BUT ! It seems that noise thr limit system do perfectly the job with ray bundle size = 1.
With ray bundle size=1, the noise thr mask is refreshed each pass, and finally converge fine. With Ray bundle size = 128, the mask info is updated only every 4 pass and infinite areas are created on last pixels (red circles with mask)

some test results : (1024*576px, using SolidRocks private beta 1.41, Bruteforce/SavedLC GI)

test1 :
Ray bundle size : 128
minAA :1
MaxAA : 100
Noise thr : 0.005
rendertime : 99% cleared in 2m05s. then locks on few final pixels until 20m40s ! (with final areas perfectly sampled...weird !they are clearly visible in final render)

test2 :
Ray bundle size : 1
minAA :1
MaxAA : 100
Noise thr : 0.005
rendertime : 99% cleared in 2m00s. then locks on few final pixels until 2m20s !

Hope it helps to locate the issue !

[Subburb]

Now testing RT GPU (noise thr : 0.005, 720*405px):

test1 :
ray bundle size : 128
Ray per pixels : 8
rendertime (approx 550KP/s) : 99% cleared in 3m20s. then locks on few final pixels until 4m25s. finally that's not so bad. it took (too much) time to polish the last red dots, but still useable "as is" with noise thr 0.005.

test2 :
ray bundle size : 512
Ray per pixels : 8
rendertime (approx 960KP/s) : 99% cleared in 3m10s. then locks on few final pixels until stopped manually after 20m !. this time red dots have been created, and became growing circles. RT don't want to stop.

it clearly appears that here again, the ray bundle size value is strongly tied to the bad noise thr behavior.

Would be nice to have a "cutoff" on the last 1% remaining pixels (or a max residual subdivs value ?), just to avoid to take ages.

EDIT : there's a workaround in RT, using the max path per pixel option.
in this case you can keep a decent ray bundle size value (128-512) and stop the final pixels computing using the max path per pixel option.
i've found that 16/noisethr value is a good balance (don't ask me why ). for example at noise thr=0.005, then max path can be set to 3200 ,for noise thr=0.003 it can be set to 5300. for noise thr=0.001 it can be set to 16000.

[vlado]

Thanks, that's definitely useful to track down the issue!

Best regards,
Vlado

[Subburb]

Cool ! Glad to give little help.
Well i just finished to integrate progressive mode into SolidRocks (little "P" button near the main render button)
Progressive quality is fully managed by SR. user have control on ray bundle size, for interactivity/speed purposes.
Seems to run fine! I've used a combination of max subdivs and noise thr to control it. this way i could avoid to reduce ray bundle size to 1 (rendertime killer).
For exact same settings (bruteforce/bruteforce) Progressive mode is slightly faster than bucket mode. Grain is different, but approx equal in quality.
The more i use progressive, the more i like it !

[wxyz]

Jerome,

When will you release the new version?

[Subburb]

it's pretty close now.
some minor stuff to test for the new save button. it's a bit tricky as i need to make difference to wich path to get/set, depends of the choice of VFB (max or vray).
i'll push a private build when it's done. Fell free to send me an email if you want to have a private try.

[Subburb]

ok now Sr 1.4.7 is on private beta stage. Did you get it ?

[Subburb]

I just tried progessive rendering with V-Ray 3.00.07.
It seems the problem have been solved. Thank a lot !!

[vlado]

We still have some issues with RT in that build; it already fixed for the nightlies though and will go into the next builds.

Best regards,
Vlado