Does Corona have problems with tall, narrow windows?

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Hello all
I'm not sure whether i need help or i need to report a bug, so first i'll try here. I'm testing a church like object (tall, with tall windows). Object itself is extremely simple, lighting is Corona sun and sky, material is just a default Corona material, all setting are on default. All openings have sky portals (properly placed), but they don't help a lot.
Still something as simple as this doesn't really clean up bellow cca 150 passes. Here are screen shots, noise is especially visible when zoomed in. I know, i know, i'm not supposed to zoom in, and if i need bigger resolution render it bigger... It's just to show it better.
So where is the problem? Well, i may be wrong, but isn't 200 passes for something as elementary as this a little - to much? How much would it take if this object is filled with furniture and reflective materials!
Another thing, those dark corners. They look like ambient occlusion is applied, and frankly, it just looks... not right.

Any ideas?

[Ludvik Koutny]

Nope, those contact shadows look right. That's how it's supposed to look. Try iRay for example and render a reference. ;) The reason it looks so strong is that sunlight bounces off the edge of the window to the left and creates bounce light, which adds more contrast between flat area and the shadowed one in the corner.

As for the amount of passes, 150-200 passes is the usual amount it takes to clean up an interior scene, so it is correct. The difference is that in simple gray box, those 200 passes will go really fast as there is nothing too complex shading-wise. In scene full of complex and reflective furniture, furry rugs and glass stuff, it may take 150-200 passes too, but one pass may take 10x longer to complete ;)

But of course, regarding performance, there could still be some bugs in UHDcache, as the way it does caching is not very reliable, and it may end up path tracing those bounces from sunlight, so you may try HDcache and see if the performance gets better :)

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I see, thanks for the info. I thought the simpler the object less passes is needed. Was expecting it to clear up in 15 passes :D

Nope, those contact shadows look right. That's how it's supposed to look. Try iRay for example...

To be honest, that looks wrong to me in every render engine. They all have that darkening of the corners, and here i am, looking in the corners, they're not darker at all. I thought it could be eyes "correcting" things, so i even took a photo of a corner once :D The ceiling did look a little darker, but not the walls. Or at least not so much as render engines make it to be. Ah well...

[maru]

It is 200 passes but it didn't take very long time to render, so you could simply devote more computing power to GI than antialiasing by increasing GI vss AA balance. Btw, what are your render settings?

I see, thanks for the info. I thought the simpler the object less passes is needed. Was expecting it to clear up in 15 passes :D

It is possible to clean after 15 passes - if you adjust render settings.

Nope, those contact shadows look right. That's how it's supposed to look. Try iRay for example...

To be honest, that looks wrong to me in every render engine. They all have that darkening of the corners, and here i am, looking in the corners, they're not darker at all. I thought it could be eyes "correcting" things, so i even took a photo of a corner once :D The ceiling did look a little darker, but not the walls. Or at least not so much as render engines make it to be. Ah well...

This is probably because of most corners you see in real life are rounded (a bit, but they are). It could be interesting to check how rounded corners of a room would look in Corona. Right now, in the room where I am, I can see some of the corners which are actually slightly "glowing", and others are darker like on your rendering. It clearly depends on light direction. The wall paint may be also a little reflective. :)

 Another thing is that adding some kind of ground plane with more realistic material (or darkening ground of environment map) has huge impact on interior lighting.

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you could simply devote more computing power to GI than antialiasing by increasing GI vss AA balance. Btw, what are your render settings?

Everything is at default, i tried AA/GI balance, didn't have to much of a affect.

Right now, in the room where I am, I can see some of the corners which are actually slightly "glowing"

EXACTLY THIS! I wanted to say this but thought i'll be pronounced crazy :D It seems, at least to me, that this "glowing" of corners happens more often in real world then darkening.

[Ludvik Koutny]

Yes, they often glow, but that depends on a lighting scenario. If you want to get glowing corners scenario, then try following:

Create a simple box with one moderately sized window in one of the walls, and point camera to the opposite wall. The wall opposing to the one with window is perfectly perpendicular to the window itself, so it will catch majority of the light at that angle, and spill the light on walls joining it creating a glow effect.

I will also try to explain why there is so strong contact shadows in this case using a picture, but i am at work at the moment, so it will take a while before i get to it :)

[Ludvik Koutny]

But even before i get to it, here are two photos of my office. Both are of the same wall, just different corners. It really just depends of light scenario:

[maru]

Some real world renders showing different kinds of corners. :)
Glowing/darkness depends on lighting and rounded-ness.

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It really just depends of light scenario

You are right :)

Btw. you need a lot more passes on these two :D