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View Full Version : whack times w/composite renders??



Johnny
02-26-2009, 09:13 AM
I have a scene with particles that takes too long to render given my current hardware.

I have read here and there about ppl in similar situations rendering things in composite layers and then putting the clips together in AE or a NLE.


is there a savings in time possible if I render my clip in two passes or two F10s? Say, I render the scene without particles, then I render the same scene with particles, but without everything else, then marry the two in FCP?

thanks for any insight.

J

Sarford
02-26-2009, 09:47 AM
It depends on how your scene is put together. If you have a camera and a background thats not moving, you can render that once, render the whole scene without it and put it together in FCP.

Comping can help reducing time, but judging from your description I doubt it will give a big time speed.

Maybe you can do the particles in AE?

flakester
02-26-2009, 09:53 AM
It may/may not save you some time, especially if your scene is raytraced in all departments.

Compositing is usually about flexibility of colour-correction and other things in post rather than time saving, though saying that; if you're rendering a static camera shot with elements that move through the scene, than in some cases it's more efficient to render one frame of the back plate, then a separate pass for your mid-ground objects, and the final pass for foreground objects.... you should be saving a heap of time there.

Not sure how FCP handles matte channels, but we find the best option is to output from LW with an unpremultiplied alpha channel.

--
flakester.

::edit:: Good call Sarford.

toby
02-28-2009, 08:30 PM
Rendering in layers can save you lots of rendertime, but only when it allows you to avoid re-rendering. The initial renders will be just as long. For example if you get render errors with your HV, you only need to render those, nothing else. Or if you find you don't like the brightness or color of something, you can change it in post almost immediately with no re-rendering.

Johnny
03-01-2009, 09:26 AM
well, that is good to know..good to know that I can, good to have that example scenario of a need to..

sounds like I'm going to have to find other ways of cutting down the render time.

thank you!


J

toby
03-01-2009, 01:34 PM
I have an old machine too, it frequently forces me to render layers, and find ways to speed things up, so lemme know if you need any ideas.

Johnny
03-01-2009, 02:57 PM
I have an old machine too, it frequently forces me to render layers, and find ways to speed things up, so lemme know if you need any ideas.


thank you..I more than welcome ideas...

my #1 way of speeding things up is to experiment with ways which are less "expensive" of CPU times but which give comparable results.

one example is replacing an area light with several spots using shadow maps. not the same as area light results, but comparable with shorter render times.

I am wide open to any ideas you'd care to share. thank you for offering.

J

toby
03-01-2009, 04:01 PM
Shadow maps is one thing I was going to mention =) that's using your noggin!
I've also used 1 bounce ray recursion ( a setting of 1 in 9.6 is the same as 2 in 9.3 ), as long as it's not a complex chrome/glass object, it frequently looks just as good. I hear that movies like Transformers and Iron Man used 1 bounce, sometimes none, just reflection mapping. I'd still use more if I had a faster machine though!

If you're using radiosity use Interpolated Backdrop, and you can reduce the Multiplier to 50 or even 25%. It's really fast.

Can you replace your particles' hv with geometry?

Johnny
03-01-2009, 10:47 PM
Shadow maps is one thing I was going to mention =) that's using your noggin!
I've also used 1 bounce ray recursion ( a setting of 1 in 9.6 is the same as 2 in 9.3 ), as long as it's not a complex chrome/glass object, it frequently looks just as good. I hear that movies like Transformers and Iron Man used 1 bounce, sometimes none, just reflection mapping. I'd still use more if I had a faster machine though!

If you're using radiosity use Interpolated Backdrop, and you can reduce the Multiplier to 50 or even 25%. It's really fast.

Can you replace your particles' hv with geometry?

Is reflection mapping just what it sounds like? you take an image of what would be the reflected item, then map it to the surface(s) onto which you'd want it reflected?

I am likin' the sound of a 1-bounce rt setting..have to try that soon.

I don't believe that I can replace this particle treatment with geometry...the real time bandit in this case is smoke, and it looks so cool, I guess I'm willing to take the hit in return for what it brings to the story.

thank you for those tips...they'll get used!

Johnny

toby
03-02-2009, 01:33 AM
Is reflection mapping just what it sounds like? you take an image of what would be the reflected item, then map it to the surface(s) onto which you'd want it reflected?
It's the 'spherical map' setting in the environment tab. It doesn't look very good because it ignores geometry around it, so it's always totally innaccurate and abnormally bright. Renderman ( used on Transformers and Iron Man ) has a reflection occlusion option which makes it look pretty good, as long as you don't see it side-by-side with real raytracing. We don't have that option, unless one of the node masters can figure a way to wire it up.

Sarford
03-02-2009, 05:06 AM
You can render a spherical map of the suroundings with the advanced camera and use that as a reflection map. Just make sure the camera is in the place of the object with the object itself hidden. It is not phisicaly acurate but most of the times it is not noticable. If the object moves, you can make a animated spherical map by folowing the same animation path with the advanced camera.

Most smoke can be made in post which is a lot faster than 3D. If you have AE with Trapcode Particular you can make 3D smoke faster than in LW. If the smoke is visible in reflections you might try to wrap it in in comp with some fancy displacement and distortion, or use polies with projected smoke to add to the reflection map.

Rendering in passes is partculary handy in problem situation, most of the time you only have to rerender a couple of passes. And also, always render frames, no animation (but I guess you already do that).