CORONA LIGHT PROBLEM

[Romas Noreika]

Hello everyone,

I started using corona after 9 years of Vray.

And I noticed one big issue with corona light plane,disc,sphere does not matter which shape it is.

So it has:

Visible Directly
Effect Reflections
Effect Refractions
Oclude other lights

So for example. Lets just say I have a quite big room and only one pendant light in the middle of the room. A put extra 2 corona planes just to push some more light in.
So I remove visible directly and oclude other lights check box. So what do I get? I get a nicely light scene, with speculars on my materials from those lights and everyhing.

But what I also get an ugly reflection in the mirror of those two corona light planes. So thats fair enough - I go to those corona lights and turn Effect reflection OFF. And there I get no ugly reflectionin the mirror of them.

But I did notice another thing that I am not getting those speculars from those two planes anymore. The materials became flat and dead. And corona light does not have a checkbox called effect speculars.

Basically if you turn OFF effect reflections you are loosing all the speculars at the same time. Which to me sounds weird. Is there a way to seperate reflections from speculars with corona light?

Thank you very much.

[pixelab]

I think it's because Reflection = Specular on a physical point of view.

Btw it's a strange workflow, where do you put those lights ? In the middle of the room? In the windows ? Don't you have enough light coming from natural/ artificial sources ?

[Romas Noreika]

The two corona light planes are in the middle of the room almost. I mean I did put them just to bump up the light in the scene. But I do not want to see them in the mirror. But I want to get the speculars from them.

My room window is quite small. Plus I do not want to push the outside light more, because in that way I will burn the windows frames completely. I just want to get the balance.

Same thing with IES lights, I was doing a bathroom scene. I had 6 spot lights in my bathroom. So the spot light had the corona  light material apllied to the spot light bulb to lit the interior of the spot light. And below there was a corona light DISC with and IES profile. Same thing I was seeing that white disc in the mirror, if I turn the reflections off the speculars of it is all gone. And the speculars that are coming from the spot light small bulb is not enough, my bathrom scene materials are not picking enough speculars from just that tiny little bulb in the spot light geometry.

And I cannot find a ways how to go around this. Corona does not have that effect speculars checkbox.  I mean I understand visible directly works perfectly, but why should I see that white round disc in my mirror reflections especially for the ies profile. I just want the effect of it in my scene. But I do not want to see that ugly white disc below the spot light geometry. Do you understand where I am going with this? :)

Thank you.

[maru]

There is no separate specular and reflection in Corona. There are no chances, and reasons, to have this ever changed.

For light sources such as lamps/chandeliers:
You can use Corona Light material with "emit light" disabled, or Corona Material with self illumination enabled (careful with this!) for the directly visible parts - such as light bulbs, lightbulb filaments, etc.
You can then create simple Corona Light (e.g. plane shape) around your light source and disable all visibility options - so that it only casts light into the scene.

For windows:
Having a super bright sky outside the window and bright interior is physically correct - you get this when taking photos in real life. To overcome this, you can either use some extreme color mapping (e.g. increase highlight clamping), or you can use a separate bitmap for the background's direct visibility (you can then lower its exposure) and a separate map/color for the environment light. This way you will get balanced exposure of the image behind the window, and the interior lighting.

Useful stuff:

Light vs Self Illumination:
https://coronarenderer.freshdesk.com/support/solutions/articles/5000515603

Backplates:
https://coronarenderer.freshdesk.com/support/solutions/articles/5000515605

[Romas Noreika]

For light sources such as lamps/chandeliers:
You can use Corona Light material with "emit light" disabled.
You can then create simple Corona Light (e.g. plane shape) around your light source and disable all visibility options - so that it only casts light into the scene.

But in this case my spot light interior will not be lit by the corona light mtl - because emit light is off.

And corona light plane gives only diffuse and shadows. Speculars from the bulb itself is not goin to be enough right?

hmmm.

[denisgo22]

For light sources such as lamps/chandeliers:
You can use Corona Light material with "emit light" disabled.
You can then create simple Corona Light (e.g. plane shape) around your light source and disable all visibility options - so that it only casts light into the scene.

But in this case my spot light interior will not be lit by the corona light mtl - because emit light is off.

And corona light plane gives only diffuse and shadows. Speculars from the bulb itself is not goin to be enough right?

hmmm.

I Agree on 100%|||
this is a big disadvantage Corona light unlike other's render's (Vray for example), but you can use Exlude/Include option, despite the fact that it is very inconvenient///
One light only for reflection's and specular's, and one for Diffuse and shadows, for the relevant objects///

[maru]

Speculars from the bulb itself is not goin to be enough right?

Why? Sorry, but I still don't understand the problem.

[Romas Noreika]

Take a look at my bathroom scene.

With you aproach corona light mtl on a spot light bulb  - emit light off. And a spot light profile DISC/plane below the spot light geometry evrything is OFF. And you will see that I am not getting enough speculars just from that small light bulb. Inside.

You can see two region renders as well one with ies profile reflections ON and one with off . Off looks flat and ON looks alive. Take a look please.

[Romas Noreika]

Because I have a spot light above the sink and above the shower head close to the wall. You should see a bigger specullar from the IES light/spot light.

I cannnot figure it out how to make this work with corona.

If I will put the IES profile inside the spot light and leave reflections ON. It will look weird.

You are saying that think realisticly. But you cannot think realisticly in these situations, because in real life that small light bulb will lit your interior. In Corona or render engine doesnt matter that small bulb cannot lit the whole interior. If it will it will cause slow render times/artifacts and a lot of noise in ur scene.

Thats why we are always faking things. Putting a light material on a bulb and include only the spot light geometry in it. Because we are not litting the whole scene with this small tiny bulb. We just need to lit the interior of the spot light geometry.

And then we are putting a IES profile below to give us the speculars/light/shadows. And we should not see it directly or in a mirror reflections.

We just need to get the effect of it in the scene which are: Speculars/Diffuse/Shadows. That is it.

What do you think about this.?

Because in you proposal with emit light off on the bulb  - your not going to lit the interior of the spot light it will be dark inside. Makes no sense at all.

Best,

Romas

[Romas Noreika]

I do not know how other people work with IES lights in corona but I would really like to know.

Because ( corona light mtl on a bulb  - emit light off. And IES profile below everything is OFF  - is not working properly.

[maru]

I will try to create some simple scene demonstrating this next week. Sorry for the delay.
I think you are just not using enough intensity for the light bulb (the one which does not emit light). But there might also be some kind of bug involved, so I am not saying I am right.

[Romas Noreika]

I am using the latest corona version.

[Romas Noreika]

I would be really greatfull if you would create an example for me. If you want I can share my bathroom scene through dropbox.

Which version of max are you using?

[Romas Noreika]

maru - will you show that example that you said? :)

[maru]

Hi RomasNoreika, I must admit that I was wrong. It seems there is some problem with reflecting light mtl with emit light off, or self illuminated materials. The reflections are there, but it looks like they are extremely hard to sample, which results in noisy mess. I have this reproduced, and I will report it straight to the devs. Sorry, I was sure that the result will be different, without actually checking it...

note to self: Tests\light-specular

[Romas Noreika]

I don't know what you discovered here maru, but I was just saying that your technique with:

corona light material - emit light off on a bulb. (I would leave emit light ON, because I want that my spot light interior would be lit, not dark)
corona light with IES profile below the spot light everything off

DID NOT WORK, I was not getting enough speculars in the scene on my materials.

Anyways - maybe one day there will be a solution for this situation with an IES light spot light setup.

Best,

Romas

[maru]

Ok Romas, in my last post I admitted that I understand the problem.

[Romas Noreika]

Also another big problem, especially in production region rendering.

Lets just say the client want to change just the sofa material or something small in the scene.

I ussually re-render just a region, why should I bother re-rendering the whole image.

So I rendered a full IMAGE in 80 passes. Then i drag a region in corona buffer and that region cleans it self up in 20 passes it is supper clean. So the question now is how the hell I should know how many passes I need to put to this region. I mean if the whole image rendered in 80 passes. That region that I draw, should render at the same quality vise in 80 passes, but those passes should be a lot faster. At the moment I have no idea how many passes I need and the region is completely different noise wise.

I did not try this with MAIN MAX region, reci it will be the same. But corona buffer region and selected element render will not be the same quality as your final image. The pass count and quality will be different.

MARU - can you please tell me how I can get exactly the same quality region as my final image rendered in 80 passes?

[maru]

MARU - can you please tell me how I can get exactly the same quality region as my final image rendered in 80 passes?

I don't think this is possible with adaptivity enabled. You can disable adaptivity, and then you will get exactly the same quality after the same number of passes, but obviously without adaptivity, the rendering will be slower. You can disable adaptivity in devel/experimental settings: https://coronarenderer.freshdesk.com/support/solutions/articles/12000021288
Once again, disabling it is NOT recommended!

[Romas Noreika]

Alright then another way of thinking.

Theoreticly if using noise threshold instead of passes threshold.

Lets just say I set my final full image to 1 of noise threshold cap.

So if I will render that region it will stop rendering at that 1 noise threshold, correct me if I am wrong? And I shouls get exactly the same quality noise vise region and full image? Yes?

[maru]

No, it does not work like that. You will get different results. For example if you have the whole image and there is a lot of contrast in it - e.g. a glowing sphere, dark background, and some flat surface like a wall, then the same noise limit will be completely different when rendering the whole image, and when rendering a part of it (e.g. a part where the glowing sphere is visible, a part where the flat surface is visible, etc.).
I can see an issue here, but currently can't think of any reliable solution other than disabling adaptivity.

[Romas Noreika]

I do not want to put Vray here again just going to say how I work with the clients sometimes,

If I need to re-render just a region I send it to a farm ant forget it. When I will open it I will know 100% that it will slap in photoshop 100% correctly no noise difference or anything else.

With corona I have to render it by looking at it and pres stop whenever I am happy or I dont know :) I am talking here about a heavy production, not some simple freelance work. :)

[maru]

I have submitted both issues (reflections of lights with "emit light" option off and different quality of region renders) to our internal bug tracker. I will be sure to report any updates here. You are also welcome to track the reports yourself:
regions - https://corona-renderer.com/bugs/view.php?id=2417
reflections - https://corona-renderer.com/bugs/view.php?id=2416