Author Topic: Path tracing comparison  (Read 376 times)

Offline sboerner

  • Member
  • *
  • Posts: 476
    • Steve Boerner Typography & Design
Path tracing comparison
« on: January 05, 2019, 05:55:20 PM »
Finally had a chance to test the path tracer. The scene is a section of my Erie Canal project and includes models, foliage, and a water surface. (The water is actually a surface layer with a reflective shader plugged in as a child.) Both renders are straight-up conversions from 32 bit, no adjustments.

The challenging thing about this part of the scene is that the foreground is almost entirely in shadow (cast by structures off-camera to the right). The standard renderer seems to have a problem with this. None of the objects in this large shadow cast their own shadows there's no shadowing inside the rowboat (on the steamer deck), no contact shadows beneath the crate or rowboat and, strangest of all, no interior shadows inside the rear cabin of the steamer or the barn.

The path tracer does a much better job and the shadowing is much more natural. The background foliage looks a bit better, too.

But the water surface has lost most of its reflectivity. Any way to restore that? (I bumped the water's reflectivity from 1 to 2 for the path traced rendering. Originally it was much grayer . . . looked like lead instead of water.)

No GISD on the standard render or surface detail exaggeration in the path traced render. The path tracing took about 8x longer than the standard render. I noticed it really slowed down when it hit the water surface.


Offline Oshyan

  • Planetside Staff
  • *
  • Posts: 13187
  • Holy snagging ducks!
Re: Path tracing comparison
« Reply #1 on: January 05, 2019, 11:35:37 PM »
Path traced version is definitely much better (although that row boat's texturing must be too bright, it stands out quite a lot).

The reflectivity in the Path Traced version is not lessened, the *softness* of the reflections is increased. :D So you should put the reflectivity back where it was first. The you should just need to reduce the Min Highlight Spread quite a lot (Reflections tab of water shader). Do a crop render of the water and try very small decimal values in the path traced version until you match the look of the original that you want. The path traced version's reflection calculations are more correct however, so you may not get the exact same look.

- Oshyan

Offline Dune

  • Member
  • *
  • Posts: 15196
    • www.ulco-art.nl
Re: Path tracing comparison
« Reply #2 on: January 06, 2019, 07:11:04 AM »
Cool to see the difference. The inner cabin shadows are the most striking. That's something I struggled with a long time with the normal renderer.
So the highlight spread should be even les than default 0.01. Maybe 0.001? Is that in meters too, btw?

Offline sboerner

  • Member
  • *
  • Posts: 476
    • Steve Boerner Typography & Design
Re: Path tracing comparison
« Reply #3 on: January 06, 2019, 03:52:47 PM »
That's exactly what it was. I'm using a reflective shader (not a water shader) so reducing the specular roughness fixes the reflections. I set it at 0.005 for this rendering. The highlight intensity is 0.25. I may dial one or the other back but this is a good starting point.

Tightening the reflections reduced the rendering time by about 20 percent (makes sense). The path tracer certainly improves the overall look. I'll try a rendering of the full scene next.

(Oshyan, the steamer's hard-working but invisible crew just gave the rowboat a fresh coat of paint and varnish. :D Just kidding. It needs to be dirtied up a bit . . . another item for my to-do list.)

Offline Dune

  • Member
  • *
  • Posts: 15196
    • www.ulco-art.nl
Re: Path tracing comparison
« Reply #4 on: January 06, 2019, 04:02:17 PM »
Strangely I tried a path trace and ray trace of water with exactly the same settings (default) and both were good. Maybe you got into problems because the reflective shader has a different default highlight spread than the water shader. Only the transparency in a water shader doesn't work, so you have to take that in consideration if you'd use one. If the water is too dark you may want to add some color.
Setting reflectivity to less than 1 (say 0.8) also reduce rendertime, and may be good enough. Ah, writing 0.8 followed by a ) produces a smiley  ???

Offline sboerner

  • Member
  • *
  • Posts: 476
    • Steve Boerner Typography & Design
Re: Path tracing comparison
« Reply #5 on: January 06, 2019, 04:12:15 PM »
I think that's what it was. The reflective shader specular roughness was left at the default of 0.1. The amount of water transparency visible in this scene would be minimal (because of the oblique camera angle) so I've been using a reflective shader instead to save rendering time. Good suggestion on adjusting the color, I'll take a look at that.

And 0.8) would be a pretty cool setting. :)

(I remember seeing earlier discussions of roughness/highlight spread settings relative to the path tracer on the forum, but can't find them now.)

Offline Kadri

  • Member
  • *
  • Posts: 8502
Re: Path tracing comparison
« Reply #6 on: January 06, 2019, 05:13:25 PM »

Render time increase is unfortunate but it looks good. Kind from a game feel to a more realistic look on objects.

Offline Oshyan

  • Planetside Staff
  • *
  • Posts: 13187
  • Holy snagging ducks!
Re: Path tracing comparison
« Reply #7 on: January 06, 2019, 09:15:36 PM »
Cool to see the difference. The inner cabin shadows are the most striking. That's something I struggled with a long time with the normal renderer.
So the highlight spread should be even les than default 0.01. Maybe 0.001? Is that in meters too, btw?

Yes, even lower than that if you want pretty sharp reflections. But no it is not in meters (I don't actually know the unit).

- Oshyan

Offline Dune

  • Member
  • *
  • Posts: 15196
    • www.ulco-art.nl
Re: Path tracing comparison
« Reply #8 on: January 07, 2019, 06:05:52 AM »
I just set it to zero to experiment and that works too. Even if also the hightlight intensity is set to zero. I don't quite understand that though, because the highlight at zero and then increasing spread (of nothing?) gives quite a difference.

Offline Matt

  • Planetside Staff
  • *
  • Posts: 3578
  • I'm the crazy one
Re: Path tracing comparison
« Reply #9 on: January 07, 2019, 12:36:20 PM »
"Highlight intensity" only applies to reflection of direct light sources, not the rest of the scene.

The "spread" parameter is different. In the standard renderer it has no effect on reflections of the rest of the scene, and that's why it was called "highlight spread" - it only affected the reflections of direct light sources. But in the path tracer the roughness is unified between scene reflections and light source reflections, so it affects everything. So the naming is misleading now, and we might change it.
« Last Edit: January 07, 2019, 12:43:02 PM by Matt »
Just because milk is white doesn't mean that clouds are made of milk.

Offline Dune

  • Member
  • *
  • Posts: 15196
    • www.ulco-art.nl
Re: Path tracing comparison
« Reply #10 on: January 07, 2019, 01:31:54 PM »
That's what I figured, the naming pulling my leg  ::) Thanks, Matt.

Offline bobbystahr

  • Member
  • *
  • Posts: 10420
  • Turn, and face the Strange Ch Ch Changes...D Bowie
Re: Path tracing comparison
« Reply #11 on: January 07, 2019, 01:41:40 PM »
That's what I figured, the naming pulling my leg  ::) Thanks, Matt.

ooooh that's gotta hurt heh heh heh
something borrowed,
something Blue.
Ring out the Old.
Bring in the New
Bobby Stahr, Paracosmologist