illuminating by plane... bug

[Dune]

It seems that the use of a plane or card to illuminate parts of a render or objects (like a flock of tundra swans, as I'm working on) is bugged. It used to work, with either just a white color or some illumination, and set to invisible, but visible to other rays.

I have quite a few files where I needed to get some light on wings of a bird, e.g. or some light on the darker side of something, and it worked perfectly. It now seems broken in standard render, only works in PT.
I hope this can be repaired, as I don't need/want to use PT for every render.

The problem is that I have these swans high above a snowy landscape, right in front of the camera, but they don't catch enough light, as the light is on quite a low angle (15º). I want to add some light to the undersides and the topsides. Can't figure out another way to do it.

[Hannes]

I'm afraid I can't confirm this. I did a little test, and it works with the legacy renderer as well, although it looks more natural with the path tracer.

[WAS]

I'm afraid I can't confirm this. I did a little test, and it works with the legacy renderer as well, although it looks more natural with the path tracer.

It's possible the light mapping calculation is more approximated at distance. I've noticed that with ambient light the approximation seems more "aggressive" in these later versions. You get round spots of light, and round spots of dark in a blanketed area, because it just doesn't know what the heck to do.

The round lighting artifacts used to just be visible with strong luminance or ambient light (like cabin scenes, or lamps, etc, where they don't cast light onto the ground right) but now I can notice it with even soft highlights, and it isn't smooth unless right in the foreground.

These sort of things bother me. We can't have unrealistic hacks in other areas to fix issues with the renderer, because it's not realistic, but other areas where realism is entirely lacking, we don't get much improvement.

[WAS]

Also have you tried just a light source and only using light surfaces?

[Matt]

It's possible the light mapping calculation is more approximated at distance. I've noticed that with ambient light the approximation seems more "aggressive" in these later versions. You get round spots of light, and round spots of dark in a blanketed area, because it just doesn't know what the heck to do.

The round lighting artifacts used to just be visible with strong luminance or ambient light (like cabin scenes, or lamps, etc, where they don't cast light onto the ground right) but now I can notice it with even soft highlights, and it isn't smooth unless right in the foreground.

I don't remember making any recent changes in this department, but the GI cache isn't good in all situations. If you have a scene that you can demonstrate renders differently in different versions, I'll try to figure out what changed.

[Matt]

It seems that the use of a plane or card to illuminate parts of a render or objects (like a flock of tundra swans, as I'm working on) is bugged. It used to work, with either just a white color or some illumination, and set to invisible, but visible to other rays.

I have quite a few files where I needed to get some light on wings of a bird, e.g. or some light on the darker side of something, and it worked perfectly. It now seems broken in standard render, only works in PT.
I hope this can be repaired, as I don't need/want to use PT for every render.

The problem is that I have these swans high above a snowy landscape, right in front of the camera, but they don't catch enough light, as the light is on quite a low angle (15º). I want to add some light to the undersides and the topsides. Can't figure out another way to do it.

GI cache settings are important. The smaller the card, the more likely the GI cache is to miss the card, but "GI sample quality" may be able to fix that. If you're rendering something that is seen by very few prepass samples (which sounds likely if it's a flock of birds), increase "GI cache detail" so that more prepass samples see the birds. If you have "Supersample prepass" turned on, try turning that off because it reduces the number of GI rays per prepass sample (although this may be OK if "GI sample quality" is high enough).

[WAS]

If you have a scene that you can demonstrate renders differently in different versions, I'll try to figure out what changed.

Well I guess I haven't specifically compared between, but it seems like it's more noticeable. I kinda wish there was almost a blur for the ambient lighting, cause that could probably hide the blob shapes. I've been wanting to do more space-y stuff and I've been trying to do more self-illuminated stuff, like the brown dwarf. And for the most part things look good in most instances, but to me, my eyes area drawn to the lighting shapes in my planet discs, or gas clouds around a "star". For others it may just be part of the art but I wish there was some way to mask it more.

[WAS]

It seems that the use of a plane or card to illuminate parts of a render or objects (like a flock of tundra swans, as I'm working on) is bugged. It used to work, with either just a white color or some illumination, and set to invisible, but visible to other rays.

I have quite a few files where I needed to get some light on wings of a bird, e.g. or some light on the darker side of something, and it worked perfectly. It now seems broken in standard render, only works in PT.
I hope this can be repaired, as I don't need/want to use PT for every render.

The problem is that I have these swans high above a snowy landscape, right in front of the camera, but they don't catch enough light, as the light is on quite a low angle (15º). I want to add some light to the undersides and the topsides. Can't figure out another way to do it.

GI cache settings are important. The smaller the card, the more likely the GI cache is to miss the card, but "GI sample quality" may be able to fix that. If you're rendering something that is seen by very few prepass samples (which sounds likely if it's a flock of birds), increase "GI cache detail" so that more prepass samples see the birds. If you have "Supersample prepass" turned on, try turning that off because it reduces the number of GI rays per prepass sample (although this may be OK if "GI sample quality" is high enough).

Would this be a case where super sampling with higher samples would help too?

[Matt]

GI cache settings are important. The smaller the card, the more likely the GI cache is to miss the card, but "GI sample quality" may be able to fix that. If you're rendering something that is seen by very few prepass samples (which sounds likely if it's a flock of birds), increase "GI cache detail" so that more prepass samples see the birds. If you have "Supersample prepass" turned on, try turning that off because it reduces the number of GI rays per prepass sample (although this may be OK if "GI sample quality" is high enough).

Would this be a case where super sampling with higher samples would help too?

I recommend increasing "GI cache detail" and "GI sample quality" to get better results. I am not confident about "Supersample prepass" and I prefer not to use it. I think it may be exacerbating the problems in many situations.

[WAS]

Good to know, thanks.

[Dune]

Thanks all! I'll try the GI cache detail, silly I didn't think of that. Here's a little detail I tested yesterday, one with PT, which is way too light but it works, the other with same settings in standard renderer.
There are 20 or so birds in a row 140m above ground. I hovered a 100x100m card/plane (tried both, no shadows, invisible, double sided) closely over it, with illumination set at different values.

I did try a spotlight (not a light source yet), but wasn't quite satisfied with that yet. I hope this GI change works....

[Dune]

Mmmmm, there was another 'problem'   I had it set to read GI cache file, and the swans were put in later... totally forgot, never checked. Sorry for any disturbance!

[Matt]

That would explain it