Splotchy renderings

[Amelia S]

Hi again,

In general, can anyone say what would cause this splotchy effect?

Thanks,

Amelia

w/ VW 2016

[Amelia S]

It seems like the more bounces of Indirect Lighting we have, the less splotchy it is. However, even with the maximum 8 bounces, we still see a bit of this.

[PVA - Admin]

Sometimes this comes from having limited light sources, which isnt really a problem functionally, there is just a little tweaking that can improve it without adding other lights.

So, the textures you use for your glass in windows and doors, edit that texture and then click "Indirect Lighting Options", inside here, check "Portal"

Its more complex under the hood, but effectively what it is doing is additional calculation to improve the quality or effectiveness of light that passes through each pane of glass. I am not sure if this is a magic bullet in this situation, but please post the resulting image for comparison either way. This is a relatively new feature and I have not played with it much yet.

[Amelia S]

Changing the glass texture to "portal" completely whited out the rendering.

But I came across something else that's interesting. In this file, it seems like [the problem] goes away when I override the viewport to turn off lights in other areas (totally invisible from here) of the house.

Then, I had to add a lot more ambient light and some ambient occlusion for any depth to be legible. The resulting non-splotchy image is attached.

Edited May 25, 2016 by Amelia S

[Amelia S]

I'm still not understanding the problem though, because in this other project, there are no light sources besides the Heliodon, and I have a similar (albeit smaller) issue.

Thanks Jim, this is so helpful.

[PVA - Admin]

Generally that splotching happens when there arent enough bounces present, we try to balance it so that you have a range of settings for things like indirect from 8 to 2, going between "This looks perfect but takes an eternity" and "just render it in 17 seconds I dont care about the details" but I suspect we need to add options for more indirect lighting bounces to properly solve issues like this without having to poke other light objects like you did.

[zoomer]

Amelia,

Do you use a 100% White with 100% amount ?

If so that can't calculate a reasonable GI Solution.

Maybe you can post a a file of that first empty Room with your setup ?

[PVA - Admin]

^ this is also true. Textures based on perfect white or perfect black can appear strangely and react to light in odd ways.

[Amelia S]

Jim,

I think that sounds about right. I appreciate having options. The rendering with furniture in it didn't take that long, although it was at maximum bounces. So adding bounces and removing lights are not the fixes for that one. We'll see what changing the white does.

Zoomer,

You may be on to something! A low-quality render looks much better with off-white than with white, in this respect. Never would have thought.

I'm about to leave some renderings overnight. I'll check back in with results tomorrow. Thanks yall!

[zoomer]

Setting a material to 100% white means it will reflect 100% of the light and

so have no absorption. The GI calculation will therefore bounce endlessly

and the image will look flat and not like in reality.

In reality even the whitest wall will not reflect more than about 70%.

So you have to set a (30%) gray color for a white Material.

As this sounds quite strange, it is easier to set the color to what you want

to finally achieve but set the color amount down to 70-80%.

Our brain does translate that, according current light situation, to be white.

You have to set the same in RW by setting the cameras exposure settings until

it looks white on your monitor and final prints.

Standard camera settings are "calibrated" to a normal Heliodon daylight scene.

If you have an interior scene with only the small window glass part to enter

that outside light into that large room - it will be much darker. Like in reality,

so you have to rise your exposure on the camera, like your eyes and brain does

to adapt to the scene.

Edited May 25, 2016 by zoomer

[J.E.]

Hi All,

I've also been having issues with splotchy renderings. Changing the point lights from 'realistic' to 'smooth' has gotten rid of the splotches but the rendering comes out darker. The Indirect Lighting is set to 'Interior, 8 Bounces' in both cases. Switching the window glazing material to 'Portal' has not had any major effects and neither has adjusting the wall material color. I've attached two images showing their comparison. The rendering time is about 15min.

My guess would be that with more light bounces there would be less splotches but other than that I'm out of guesses,

Thank you

[Amelia S]

Zoomer, that is really interesting. Thanks for the explanation.

JE, I'm still struggling with this too. Does your render style include Ambient Occlusion? That's one thing that's seemed to have a positive effect for me.

[J.E.]

I have Ambient Occlusion turned up to 100. The only other thing I can think of is that I have too many point lights in one scene, I'll have to see if that makes a difference.

Amelia, I've attached some screenshots of my Render Style settings to compare.

[zoomer]

Ambient occlusion happen in, or from, edges only.

It will not effect GI, it will be an overlay only.

The only way it could effect the middle of a wall is when setting really

large distances that it can reach that region at all.

(If I read that right he has 100", about 2,5 m, which would be not very realistic

and could lead to problems)

What I see in his both images are splotches though.

Interior renders are always harder for a GI.

Like exteriors with daylight setting, the more light one pixels sees around itself,

the faster and cleaner the GI works.

In an interior where only a few faces are bright, together with a high contrast to

the rest, the examining rays sent to calculate that pixel will hardly find that light.

So you will get quite different brightness values for neighboring pixels, which looks

splotchy.

[J.E.]

Zoomer,

The Ambient Occlusion is set to Strength: 100 and Size: 10'0". Is that a realistic size? Is it based on average surface dimensions (Length x Width) in the model?

If I'm understanding you correctly, the rendering is splotchy because an interior rendering may create more contrast between pixels? It would be nice if there were a way to get the GI to work cleaner. Letting in more light may help but I'm surprised I haven't seen more splotchy rendering posts.

Thank you

[Amelia S]

I would argue that in JE's "realistic falloff," there are splotches around the edges of the screen and the edges of the window. I think that all of my attachments in this thread have more splotches near edges than on flat expanses.

My ambient occlusion in my best rendering so far is set to 20% and 2'0", so that's a little different.

Sorry if this is not the solution, but I figured it was worth mentioning.

GI means global illumination right? Zoomer, are you just talking about the overall effect of indirect light, or something more specific?

[zoomer]

If you can post a file, reduced to that room, then I could take a look at

all settings in general.

But 10' (about 3 m) is too much and far from reality.

But ambient Occlusion is not realistic anyway, it is just an effect.

AO is meant to pronounce concave edges.

Like on a stair, the front part of the step will see the whole bright sky hemisphere.

while the part at the edge will be shadowed by the next step and only sees one

half of the hemisphere, so has to be darker.

This is what GI will do anyway in a real way. But as it is too coarse, those edges

may look unrealistically flat in renderings.

Therefore it is an effect, similar to dirt shaders in other software to improve coarse

GI setups. You can even take it to simulate GI like look.

It will start from the edge darkening by the value you set in % and gradient that to

0% after the length you set, similar to a soft shadow.

So realistic distance may be 3" to 12",

The percentage I use is around 30%, as it tends to easily look dirty.

[zoomer]

Yes I meant Global Illumination by GI.

It is a complex subject,

I try to find a balance between overall and some of the specific details.

Explaining is not one of my strengths

[Amelia S]

You're a great explainer!

[zoomer]

And I do not want to sound negative to AO because calling it an effect only.

AO is one of the great features of VW 2016,

it can help to make look your renderings more realistic and it does a great job to

make OpenGL look much better.

[Dave Donley]

Splotchiness comes from the renderer when it is sampling the scene finding some samples with super bright values that are much different than the average values. This can happen when bright light comes into the scene through narrow holes which is why the Portal option helps with window glass textures (that was my first thought but Jim mentioned it to you, I agree Portal should be turned on for the window glass).

Or from bright lights bouncing around very close to surfaces, like the classroom model. A Glow texture assigned to the white parts of those fixtures would probably render much smoother. The Portal option might also help because it is a scene with sunlight coming in through the windows as well.

For interiors use the Interior indirect lighting setting, it does more work that will help reduce splotchiness too. I.e. don't use the Exterior choice when you are rendering an interior.

[barkest]

Make sure your lights are not close to an object such as a ceiling, wall etc. For a test move the light source well away from a close object and re render.

[PVA - Admin]

If anyone who encountered these problems could test them in 2017 and report the results back, that would be fantastic. Thank you!

[Luis M Ruiz]

About a year ago I remember attempting something unusual with our software, a still life scene, why not?  in the process I captured one of my earlier renders and realized those were not bubbles but splotchy effects. The advised I received helped tons, I had too many light sources bouncing lights everywhere, probably more than  five, so in the end I was able to achieve the effect I needed with just a single spotlight and some small glowing objects.

[Markvl]

@Luis M RuizLooks great!  A big improvement over your original.