Absolutely dumb Iray rendering question

bicc39

A few details;

 For what I am working on, I try and schedule 3 major renders a day, built around daily chores.

The one in the evening is the major one, I try and complete everything before about 6 pm, and institute a render

for size, quality etc. This render is done while eating, watching tv, etc. Come back to the computer about 10:00pm and hope

all is well.

Now. for certain renders at about this time the rendering percentage is about 99%. If I scroll the screen ,the image looks fine.

Lately the 10 oclock 99 percent render is taking about 2 hours and longer for the final percentage. Since I do not want to stop it and do

not want to leave the computer on all night.....I wait......and wait.......and wait......and wait....for 1 percent

At this point I have so much time invested in the image I refuse to stop it but.....

Questions:

1. Is there a way to stop the render and keep the resulting image ( cannot use screen print because size is 16X20)

That I can see there is no difference that the 1 percent 2 hours makes in the quality.

2.. I know that I can set a rendering time limit, if I were to set a time of say 4 hours would that make

an enormous difference in the resulting quality. All else being the same

Should mention that the final result is printed, framed and sold as a 16X20 inch "fine print". So the final quality is an issue.

Thank you

 

MelanieL

1. If you are rendering to a New Window then yes, you can manually stop the render and save the image. You need to click on the "Cancel" button in that new window not the Cancel button in the progress window - the buttons along the bottom will then offer "Resume" (continues the render from where it left off) "Save" and "Close". You need to type in a file name to save then the "Save" button will be un-greyed and you can save the image. Note this will close the window so you can't resume after saving.

2. Sorry, I don't really know.

Richard Haseltine

The Save button under the render shjould work, as should File>Save last render. Also you can stop the render but leave the window open, put the machine into sleep mode (that is, don't close applications) and restart the next day.

bicc39

Thank you both, cannot fully convey the level of frustration, one night sat for about three hours, bug-eyed, for 1 percent

Tobor

As always, Richard's suggestion is spot-on. You can use this technique to save multiple versions of the file throughout a long render. (But know that when you start and stop renders, Iray tends to lose a bit of efficiency -- and it complains about it as warnings in the troubleshooting log!)

That said, the convergence percentage is an *estimate* performed by Iray using wholly computed metrics. What is suspects are unconverged pixels may in fact be perfectly converged and done pixels. The reverse can also be true: it can consider an image "done," but it's still very grainy.

Always go with your own human judgement. Iray doesn't know art. All it knows is how to calculate values of pixels, and compare them with a one-size-fits-all algorithm in the hopes of being able to determine when a render is, to its little brain, complete. Its pixel convergence estimates should only be considered just that, estimates.

Bobvan

Agree with Tobor I let it run unlimited until it looks good to me

alexhcowley

There is no such thing as a dumb question - there are only experts who have spent so much time doing something they've forgotten what it's like to be a beginner.

Cheers,

Alex.

AndyS

Hi,

 

there is a nice chance to collect intermediate results.

If you cancel a render, you get a r.png in the temp directory /Temp/DAZ 3D/Studio4/render.
You can copy this into a different location and resume the render. You can repeat this any time you want.

And yes: it is dump! For the last percents you have to wait longer as for the first 95%.
Under certain conditions there are grainy areas resulting of specular reflected light that only are resolved over 98% of coverage.  --> STRANGE !!

 

Andy

mjc1016

AndyS said:

 

And yes: it is dump! For the last percents you have to wait longer as for the first 95%.
Under certain conditions there are grainy areas resulting of specular reflected light that only are resolved over 98% of coverage.  --> STRANGE !!

 

Andy

Not strange at all if you understand the math behind it...

AndyS

 

mjc1016 said:

Not strange at all if you understand the math behind it...

If you know more, please explain.

I don't use DAZ commercially. Only just for fun. So I can't allow myself to own those expensive special GPU cards.
But with these long render times it isn't fun anymore.

Tobor

Some of this is conjecture, because nVidia doesn't release this type of technical detail to the public. So with that in mind:

The driving force here is how Iray *estimates* pixel convergence, the (only) metric the program uses to determine when an image is considered "done."  Pixel convergence is based on an algorithm that includes, from some technical statements made by nVidia as well as empirical evidence, the following:

1. A confidence level of any given pixel's correct value based on many separate ray samples to that pixel. The closer these values are, the more confidence Iray has that the pixel is converged.

2. A "nearest neighbor" comparison, where pixels close to one another are examined. Pixels with very wide variances from some statistical average or mean are possibly not full converged, so Iray spends additional time on them to make sure. This is one reason why textures with high frequency noise or specks, like small metal flakes, take longer to render.

There may be other signals in the algorithm, but these are likely the strongest.

Light-colored pixels caused by specular highlights are most likely fireflies, and these will take much longer to converge, because of both algorithms. We want to avoid fireflies to begin with, which is why nVidia and others suggests scene settings that avoids unnecessary brightness -- not using pure white colors for textures, for example. These rarely exist in nature, anyway.

Some basic guidelines here for avoiding the causes of fireflies:

http://irayrender.com/fileadmin/filemount/editor/PDF/iray_Performance_Tips_100511.pdf

mjc1016

Basically, internally, all Iray is doing is solving a series of equations, over and over, until it reaches what it was told to consider as 'done'...and for those areas, like Tobor mentioned, that are harder to call finished, the longer it will take to go through them.  And if you break down the shading and lighting models used, they are differential equations, transforms and other mind numbing forms of calculus...

AndyS

Wow thank you.

That are good hints. But on the other hand they are funny:

"Adjust texture resolutions to the scene requirements.

§

Textures compete with geometry for the GPU memory. The higher the resolution of textures, the less the memory available for geometry, and vice-versa.

§

High frequency textures at high resolutions may become a source of further noise and require more time to converge."

If you have low res textures you get those diagonal crossed checks, as you see in the attachment. I doubled the resolution of the texture and they're almost gone. So that's a dilemma.
For better quality of the environment you get more trouble with iRay.