Graininess in Iray renders...

MGMOZ

G'day All,

I need some basic guidance to solve the graininess in some of my Iray renders.

I am using DAZ Studio 4.9 with Iray for the rendering.

The problem is that, in a few of my pictures, not all, I can't get rid of the graininess in the render. In amongst my research, I have read that, as I am using the DOF, I need to up the light level. I tried  a fair few different levels but the grain is still there! What am I doing wrong??

I have tried adjusting the rendering settings that I understand...and ones that I don't... but without any luck so I have come to a frustrating standstill hence this rant.

I have looked through the online DAZ 3D documentation and, so far, it gives a list of the various adjustments but there are gaps in my knowledge that I am now trying to fill.

Any suggestions?

PS I neglected to mention that I am using planes & spheres as Iray emissives as my light sources

Tobor

Best to post an example, assuming it's safe for work. What some people see as "grain" is actually fireflies, and the way to get rid of those is completely different.

Assuming it is the so-called grain from un/underconverged pixels, just boosting the light alone doesn't always do it, depending on the source of light. Iray has more trouble with indirect light sources, for example. Using the Architectural filter can help here, as can "cheating" with other light fills.

Some folks will suggest upping the render convergence/quality settings, which isn't bad advice, but it puts the cart before the horse. It's best to try to address the main problem first, if you can.

 

MGMOZ

Thanks Tobor, I think I understand the Firefly concept and I'm trying out the filters involved.

I've attached a image that rendered overnight just so you can see what is happening.

There are two light sources actually inside the cab of the truck (one in the back & one in the front) plus one outside both windows of the sleeper compartment so would that eliminate the indirect light issue? Could iray have issues with the number of light sources maybe?

Lyoness

your render needs to cook longer.  go into progressive rendering and increase those values by A LOT. 

for promos, I start around here: Max samples: 12000 /max time: 20000  /rendering converged ratio: 98%

sometimes I even go higher than that.  Hope this helps.

TheKD

My method is to make it really simple.

1)I turn time to zero, so it will not take time into account at all. I crank min samples to at least 15, max samples absurdly high like 5,000,000 and convergence to 99%. This way, you are really using render quality setting to control it. It will always be convergance that stops it.

2)Render at say 5 quality to start, if not good enough, don't close render window.

3) Bump quality up to 10, then on render window hit resume. Keep doing that until good enough for you.

Tobor

There are a combination of unresolved pixels and fireflies in that image, and determining the cause can be left to process of elimination.

Interiors are always harder for Iray to render, especially when (as it appears in this image) the light is indirect. Not knowing your experience with Iray or rendering with it, this is my usual advise:

1. Remove the set and leave just the character.

2. Apply the default Iray rendering settings (if you want to capture the ones you're using, you can save them). This undos all the possibly unnecessary settings you've made, and starts you fresh. The settings you want include the "Ruins" HDR image, and default tone mapping.

3. Turn the camera headlamp off (Never) setting in the render parameters.

4. Temporarily disable (hide) any light sources.

5. In your particular case, turn off DOF.

6. Do a test render. The scene will only be lit by the default HDRi. It's not meant to be a pretty picture, just determine if other issues like various material shaders are coming into play,

You've now reduced the scene to bare essentials, and you can -- one by one -- add in the elements you want to use. Keep doing test renders. For reasons of practicality, they don't need to be bigger than 500x500. All you are doing is testing if you can achieve convergence in a reasonable amount of time.. As you add the desired elements back in, you'll likely find the one(s) that cause the issues, and with that, look for ways to resolve the problem.

Do also consider, as tests, changing up the materials for your character (save the scene, and revert as you need). That chest hair is probably causing some slowdowns.

I don't like to just throw rendering time to solve this problem. All things being equal, for a very slow scene Iray is trying to tell you something, and you need to listen to its complaints. It's better to resolve the underlying cause than to just make all your renders abhorrently time-consuming.

MGMOZ

Many, many thanks, Tobor, Lyoness & TheKD,​

I tried all your suggestions with little success. When building the original image,  I had been trying all sorts of additions (including a dynamic sheet) and I think I must have added something that messed with the file & render too.

I have ended up abandoning that file & building the image again from scratch in a new file. The result is much better other than a small number of fireflies.

Your help is much appreciated.

Cheers

Roman_K2

I've noticed that I sometimes go off the rails somewhere on a render, and Iray doesn't like some setting or some residual light that I've inadvertently put in.  I get very faint (or very bright) surfaces and a lot of grain.  Seems to me sometimes starting over is the best way to go.

Marshian

I found this starter content render setting recently that works very well, even if you set the samples and time back to default. See attached. Main cause of grain for me has been from bounce light so I have been trying to compose scenes that don't have or show ceilings, niches, etc.

I think all of you are going to love this! Check it ouuuuuuuut!

Marshian

However- If you decide to embrace the grain I made this faux product for April Fools day- IGRAYN.