Why grainy render?

reserv888

This is a weird thing that just happened. When I changed outfit, the render quality got grainy.
The only thing changed between the left and the right render is the outfit but as you can see the face is (very) grainy in the right image.
The left render took about three times longer than the right one. 
I switched back to the first outfit and the render quality was good again. I have rendered lots of outfits today and (so far) this has only happened once.

I am just curious how Daz Studio works and try to understand what causes this oddity.

Richard Haseltine

Don't delete your attachments after pasting the links into the text, they are what the link is pointing to so now there's nothing to see.

reserv888

I could see the image in my browser so I assumed everyone else could too.
I hope the image is there now.

Thanks Richard for the heads up.

Padone

reserv888 said:

The left render took about three times longer than the right one. 

That's probably why it's not grainy. Do you mean the rendering stops grainy ? Can't you let the grainy right one go on rendering ?

 

reserv888

Padone: I understand the short rendertime is why it's grainy, but it is DS studio that stops render after about a minute. Render at 100%.

The render settings are identical. The only difference is the outfit. I have caped the render at 5000 iterations (or 7200 sec) but it is nowhere near that when DS considers the render to be 100%.

Padone

Yes, I asked twice because this seemed too odd to me. So you have an outfit that stops iRay renderings .. That's very interesting. Can you please link to the product page ?

You can try by pressing the default button in the render settings just before rendering. To be sure everything is fine. Also you may check the log to see if there's any error. And if not, to check why the rendering is finished. With the default settings it should say "convergence threshold reached". As a last resort you may try disabling the render quality so you can be sure it goes on until it reaches max time or max samples.

My guess is that iRay meets an error before convergence so it should be in the log. If it's an error you could contact the PA to report it so he/she can fix the outfit.

reserv888

Thanks  for your reply Padone.

When i try to read the Log file  I can't find anything that indicates an error in the render process.
In the log file  the phrase "convergence threshold reached" ends the rendering process, but I don't know what thresholds that might be.

The outfit in question is: Goth Outfit for Genesis 8 Female(s) - SKU 46645.

Setting the "Rendering quality enabled"-button to OFF solves the issue with grain.
I made my initial question though, to better understand the Daz Studio machinery. Why does  achange iin outfit lower the render quality change AND decrease the render time.
I would have understood the problem if the outfit was more complex and needed more render time to finish, but in this case it is DS who cuts render time AND quality of its own.
I am just curious what happens and what causes it.

Sudden issues with graining occur from time to time (for me at least)  and If I can grasp the reason why it might save me alot of rerenders.

Padone

The convergence threshold is that specified in the rendering quality, that's why I advised you to turn it off.

As for why it happens, it's a mystery to me. It should not. My only guess is there could be something in the outfit materials that "fools" iRay but it's very unlikely. From the asset page I see it has settings both for iray and 3delight. So I suppose you're using the iray settings. You could also try the 3delight materials and see what happens. Often iray can render 3delight materials just fine with its "on-the-fly" conversion.