How to prevent 'Buckets' from wasting time on rendering pure White or Black background

[RobH22]

I can't believe this has not been asked. I can't find a post anywere about it. I'm rendering huge files, over 10K. They have pure white 255 or black 000 background. The render buckets waste a lot of time tracing around them, faster than if there was geometry, but still a lot of time running around on nothing.

Is there a way to prevent the background from being parsed by the buckets?

[fixeighted]

Look at it from the point of view of the renderer. It doesn't know what you find important in the scene, or indeed what exists in any given scene in any meaningful way before you press 'render'.
It merely takes the frame and assigns buckets to it all, going through the motions of looking at each bucket's information (or lack thereof) before moving on to the next.
Whist naturally it's annoying, I don't imagine there's any other way to do it, but I'm happy to be corrected

[RobH22]

I get all of that of course, but we have so many ways to exclude and include things. I assumed there was a way to just exclude the default background from being processed at all. I mean, there is a clear distinction between the default background (or nothingness in an empty scene) and then anything we create, right? I seem to recall a setting 10 or so years ago that I used that told the renderer to alias or not alias the objects from the background. There was an obvious distinction of what was "background" and what was created by the user in the foreground.

Ok well maybe it can't be done. It would be nice. Thanks.

[DCHA34]

That's a good question.
Back when I was using Lumion, I asked the same question on their forum about the very long calculation time just to render the alpha layer.
I never got an answer.
I hope Chaos will reply.

[suzanne_doherty]

Could you use render masks, so you're only rendering the geometry?

[RobH22]

Yes, I'm only rendering the geometry and separately the shadows on a Shadow Catcher. But, those are separate passes. I render the Shadow and a Reflection as two separate passes and the Geometry pass is just the geometry, lit nicely.

I'm doing a region render to block off some of the unnecessary space. The project is 3d pull handles and knobs being placed over existing photos of bathrooms, bedrooms and kitchens. The geometry in most occupy maybe 5-10% of the pixels. But they still take a long time to render and even as the buckets are faster over empty space, I sit and watch them crawl around the emptiness.

What do you specifically mean by render masks? I'm not new at 3d work, 30-years, but maybe I'm overlooking something obvious that I've forgotten about.

[RobH22]

Ok, I'm reading about something I've seen a 1000 times and have overlooked options in it, 'Image sampler (Antialiasing)/Type/Selected'. 'Selected' is not something I normally need to do in my work. This could be a 'duh' moment. Reading about it now and it could be the perfect solution for my geometry anyway.

[RobH22]

suzanne_doherty Thanks for reminding me we have 'Render Masks.' It's solved one of my problems with this project. The meshes diffuse pass now renders just the mesh and there is no processing of anything in the background.

I have just one other bottleneck. I'm rendering a separate 'reflection' pass of these objects against a matte shadow catcher plane. The reflection is very, very faint on the whole plane far away from the geometry so the render is parsing and rendering all of that faint, like RGB 001 density. Is there a way to 'Clamp' the render so anything under a threshold does not get considered and rendered?

[Joelaff]

One method is to use animated render masks. These could be made using the alpha of a previous render if need be.

Also, with a lot of empty space a large bucket size (128 pixels) will let fewer threads waste time on the blank space and generally make things faster. A higher min subivs setting also slows down refereeing of the empty areas. If you can get away with lower minimum that will help.

Of course a render region is the most efficient method, but that assumes your region of interest is a nice rectangle. Deadline will let you track a render region around moving objects. Though it’s masking doesn’t work as well if you are trying to use the VFB vs Max’s region.

[fixeighted]

I don't know if it'll help specifically but as masks are also slower to render with Vray for the same reason, you can always use the now ancient, yet still useful, scanline for those (animated ones), which render in seconds, so that's a good trick for certain things.

[RobH22]

Joelaff Very intresting things to consider. I'm not animating which simplifies things but you give me some good tips. I wish we could 'paint' a render region, something that would tell the buckets, "just don't go here." Maybe a useful feature for the future. That's fun to say 3 times fast. Yea, render regions aren't necessarily nice rectangles.

I'd still like to find a way to clamp or exclude calculations if the rays return a value below a certain threshold. That would totally solve my problem.

[Joelaff]

Oh, if it is just a still then just hand draw a mask in photoshop or something and bring that in as a render mask (as others have pointed out). Make sure it is set to Screen space.

Also, for some reason I have sometimes had problems with VrayBitmaps for Render Masks, so I tend to use traditional Bitmap nodes for those. I am not sure I was ever able to nail down the issue. Perhaps the VrayBitmap was changing itself back out of screen space, or maybe just Max crashed before I saved that change (in multiple scenes... still possible). Maybe it was due to the delayed loading of VrayBitmap. But I have yet to have a problem with a Bitmap node set to Screen space. (All my issues were only when net rendering.)

[RobH22]

Really, you can draw a render mask? I love that in 3D we can learn new things everyday. We tend to use-what-we-use and often things get overlooked. I can’t wait to try this, drawing a render mask. No one has pointed that out specifically unless I missed it. Thanks for reiterating it. I can’t wait to try it. Thanks….

[Joelaff]

https://docs.chaos.com/display/VMAX/...th+Render+Mask

Use By Texture. Use a Bitmap node to load the texture and set to screen space. Anywhere non-black in your mask texture will render.

[RobH22]

I’m out of the office right now and I’m so excited about this I almost considered ditching my fun outing and coming back to try this…lol… Prudence prevailed and I’m staying out and playing but as soon as I get in I can’t wait to try this. It always amazes me what techniques we forget about in the millions of things we try to keep track of mentally. Each new project brings new demands and requires new solutions. I wish I had run across this years ago. Can’t wait to try it.