How to clean up darker/shadowed areas of renders? Tweet

[Petec]

Just like the subject line says I am looking to clean up darker/shadowed areas of renders, particularly for interior scenes rendered using the path tracer kernel (i.e. so I can use sub surface scattering). It seems it takes an awful lot of samples per pixel (i.e. time) to clean up darker spots with my current techniques/setup.

Any tips and tricks would be welcome.

As I am looking to do this for animation purposes, it's important to be able to do this before applying the AI denoiser, as the denoiser doesn't seem to be consistent across different frames (i.e. it gives me a blurry flicker).

[face_off]

Try adjusting the Path Termination Power. http://blog.physicalc-software.com/2016/03/before-you-submit-octane-support.html

Thanks

Paul

[Petec]

Thanks I tried that and a few other tips on the page you sent (I had lighting coming in through glass/specular material). Sadly the sp count I'll need for this one is still pretty high. I'll just have to let each frame cook for longer I guess.

Thank you though I appreciate your help regardless.

Try adjusting the Path Termination Power. http://blog.physicalc-software.com/2016/03/before-you-submit-octane-support.html

Thanks

Paul

[frankmci]

I'm not a Poser user, but if you have multiple light sources, turn down the weighting of any lights that don't significantly contribute to the shadow areas. The AI light is nice, but for relatively simple lighting setups, I find hand tweaking is well worth the effort. That will help you spend your sampling budget where it is really needed, potentially saving an awful lot of time.

[elsksa]

Frank is spot on.
In complement, perhaps this and that can help.

[Petec]

Frank is spot on.
In complement, perhaps this and that can help.

Thanks to you and Frank for the tips and links. I think what I could use here is a portal plane as it's a room being lit (mostly) by daylight coming in a window. The problem I have is that the window is in the centre of the frame and I need to have some glass there. As I understand it a portal plane is not visible in render and you're not supposed to cover it with a glass material?

[elsksa]

Non-exhaustive list of random thoughts/tips:

• do not hesitate to support the primary day-light source with camera-invisible area-lights, especially in dark areas where light bounces are expected or just to have more control.
• render layers could be beneficial in some cases, requiring an assembling in post (comp).
• I haven't done it yet, but the Photon Tracing Kernel might "perform" better than PT with that glass-window. It would theoretically handle caustic paths with [more] ease compared to it.

[Petec]

Thanks for these I appreciate it.

Area light: I did add a low poly square plane on the other side of the room (behind the camera) and turned it into an emitter. That helped a bit but not enough. It's a texture emitter and the diffuse is set to white, so that might be causing some noise here based on the lighting page linked above.

Render layers: This is for an animation, so for the time it would take to render out multiple sets of frames and composite them I might as well jack up the max samples instead and let the gpus do the work.

Photon Kernel: Hmm, I'd like to experiment with this one. I do have some sub surface scattering going on in the scene as well. Any idea on how well the Photon Kernel handles SSS (if at all)?

Non-exhaustive list of random thoughts/tips:

• do not hesitate to support the primary day-light source with camera-invisible area-lights, especially in dark areas where light bounces are expected or just to have more control.
• render layers could be beneficial in some cases, requiring an assembling in post (comp).
• I haven't done it yet, but the Photon Tracing Kernel might "perform" better than PT with that glass-window. It would theoretically handle caustic paths with [more] ease compared to it.

[frankmci]

Don't be afraid to totally fake the illumination coming in from outside. Hollywood has been doing that very well for decades; you've probably seen it hundreds of times and not noticed. I'll often use a distant spotlight narrowly aimed at each opening for the direct Sun, plus a simple surface with a pale blue to green/dark gray/brown/whatever is an appropriate luma gradient on it, again for each opening. This way it is easy to make sure that the vast majority of rays are actually going into the structure where you need them. You can also individually set the sampling rate on each light source, giving you a lot of fine control. You can still use your HDRI as a backdrop without it actually illuminating anything.

And of course all the classic lighting director's tricks apply too, with bounce cards, suplemental hidden lights, gobos, gels, etc. The magic happens within the four sides of the frame, and anything not seen by the audience is totally legitimate.

[Petec]

Thanks I'll try to keep that all in mind. In this case I picked a set and multiple cameras where I kinda need the lighting to look organic/built into the scene (i.e. at some point the whole set is in frame). Adjusting the sampling rate on each light I am new to. Questions:

(1) Can I set the sampling rate on the sun/planetary environment (as it's on the settings tab in the Poser plugin, not the materials tab)?
(2) As I understand the sampling is a weight to tell octane how to prioritize light calculations? So if one light is set to 2 and the other to 100 that's a 1 to 50 weight difference and the first light will get cleaner a lot sooner?

Don't be afraid to totally fake the illumination coming in from outside. Hollywood has been doing that very well for decades; you've probably seen it hundreds of times and not noticed. I'll often use a distant spotlight narrowly aimed at each opening for the direct Sun, plus a simple surface with a pale blue to green/dark gray/brown/whatever is an appropriate luma gradient on it, again for each opening. This way it is easy to make sure that the vast majority of rays are actually going into the structure where you need them. You can also individually set the sampling rate on each light source, giving you a lot of fine control. You can still use your HDRI as a backdrop without it actually illuminating anything.

And of course all the classic lighting director's tricks apply too, with bounce cards, suplemental hidden lights, gobos, gels, etc. The magic happens within the four sides of the frame, and anything not seen by the audience is totally legitimate.