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Raytrace - what are the best techniques for speedy tracing?
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Hi Guys
Firstly, just a bit of background...
I've been an Imagine user since the Amiga days, and IFD user since mid-90's.

I'm just an amateur 3d enthusiast with a passion for space exploration and similar subject matter. My usual focus is animation, rather than single-image compositions. I like to "visualise" space-craft designs and concepts via animation.

Most of my anims are around 1000-2000 frames, so high-quality traced videos can take weeks to render on my dual core Intel!

I've used a lot of "tricks" and workarounds in the past to try and get trace render times down to a reasonable level (eg. tweeking the Resolve Depth in the Render requester, using negative-light-sources for fake shadows in scanline mode, rendering the background imagery in scanline and the primary objects in trace mode, then combining the two via Global Actor Background Image parameters, reducing scene complexity, etc, etc)

I did a search in these forums on TRACE and RAYTRACE to see what others are doing in this regard - did not get any useful results

What parameters or stage considerations do I need to heed in order to ensure the fastest trace times for a reasonable quality? I'd love to hear some suggestions - bear in mind my output is always for animations.

Thanks for taking the time to read my long post - I know there are some very advanced users here and if you could take the time to point me in the right direction, I would be absolutely stoked!

Posted on: 2009/9/14 23:42
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Re: Raytrace - what are the best techniques for speedy tracing?
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I am sad to say that my experience in animation is not so high, others here will surely answer with more experience... and basically, with you doing animations already, you probably already learned a lot more then many others.

However, depending on the animations, why are you using imagine itself to combine them?

I would probably render separate animations, just as you have done, but combine them outside imagine in some editing software like Premier or its likes...

That would give you more tweaking abilities with the different parts to instead of trusting imagines lighting system... also, since the two most time consuming things in imagine is refraction and the number of lights, rendering without refractive surfaces and with one light at a time and then combining in an outside editor will probably save a lot of time after the learning curve is done.

Doing animations, you probably already use some kind of video editing software already anyway, so the step might not be so big.

Posted on: 2009/9/15 7:02
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Johan Andersson the Impulsive Imagineer
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Re: Raytrace - what are the best techniques for speedy tracing?
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Hi Johan, thanks for the reply...

Yes, I try to keep light sources and reflective surfaces to the minimum number absolutely necessary.

It is not the actual video editing and post-processing that is the problem - I use Cyberlink PowerDirector and VirtualDub to do all that and they're great

The problem is that raytracing 2000 pics takes a very long time. I am seeking suggestions for improving raytrace speed.

The video compositing within Imagine that I was referring to in my original post is just a method I've come up with to make rendering faster. It's really just a multi-pass technique. Works okay in limited situations, such as when you don't need shadows on the background imagery (eg. the flying-car in my image HabitatFlight was raytraced but the habitat in the background was done in SCANLINE).

I've used a lot of desperate tactics to get quicker rendering results. One time, I started two instances of Imagine loaded with the same staging file. I then setup one to do the odd numbered frames and the other to render the even numbered. I used Task Manager to lock the affinity of each Imagine instance to its own CPU, and started them. It worked! Using this method I rendered the total number of frames in about 65-75% of the time compared to using one Imagine process to do each frame in sequence!

But when you are doing 2000 frames with each raytraced frame taking up to 2 hours or more, even a 35% time reduction is still a long time

So I was wondering what other users do to improve the speed of rendering especially in TRACE mode, while still getting a reasonable result.

Posted on: 2009/9/15 11:55
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Re: Raytrace - what are the best techniques for speedy tracing?
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Well, we have many users here, some even answer questions :)
And I understand that rendering 2000 frames will take a long time...

I have been mailing with Mike about continuing/redoing the Imagine software, we are in a pause right now but I hope it will continue soon, but one part of that was that I was hoping that it would be possible to multithread the rendering AND possible make it a separate net render thingy too, so that one could throw this kind of work at a render farm, nothing came of that part so far, and I haven't gotten access to the code as of yet so I don't know how possible it would be to multithread the rendering process, if nothing else it should be possible to start a line per thread at least... and do it X times faster.

But as I said, for now we are at a standstill in the talks, hopefully they will get back to me again soon.

Posted on: 2009/9/15 14:04
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Johan Andersson the Impulsive Imagineer
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Re: Raytrace - what are the best techniques for speedy tracing?
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Some simple things to speed up things...

Use imagemaps instead of procedural textures. if you have to use procedurals to get a desired effekt, produce the imagemaps with them and map those :)

Use as few lights as possible, preferably just one its better making multiple passes, one per light, and combining them outside imagine then rendering many at the same time.

Depending on what you are doing, raising the image size while lowering the anti aliasing and doing that externally is also a viable trick to save time... Probably works even better if you need to "green-screen" stuff together.

Once again, I am no pro in this... :)

I hope some of our other pro's will add and correct me :)

Posted on: 2009/9/15 14:13
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Johan Andersson the Impulsive Imagineer
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Re: Raytrace - what are the best techniques for speedy tracing?
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Assuming that some of the pix you've posted (neat stuff, btw) are stills from your animations, two hours per frame is not a bad rendering time, especially for 720p fully traced work.

Given the rock bottom costs of PCs now, if it was in your budget I'd say get a couple of more PCs and get a rendering farm going. That would not only speed up your animations but it would get you past Imagine's 9,999 frame limit.

Having said that, one thing that I do (similar to what Johann said) is to turn off Imagine's anti-aliasing, render about 25% larger images (on both axes) than I need, and scale them to size with Photoshop or another batch processing application. PShop will antialias them nicely when you scale them down and get rid of the jaggies much faster than Imagine can do it during the render.

Also, I could not tell by your post, but if you are still cooking frames with IFD you should know that deep changes were made to Imagine's rendering engine during the 3.0 cup process and the render speed of IFW is way faster than IFD's.

Posted on: 2009/9/15 16:59
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Re: Raytrace - what are the best techniques for speedy tracing?
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Hi. All,

Throw this in the mix- it works on the Amiga version at least and works in IFW 1.0. for single frames (It was originally in one of the IML Digests.)

Create an Axis and position it at 0,0,0. Then scale the axis in each of the three axes until it only just completely encloses all of the Objects and the Camera in the scene. In the Objects' Transformation Parameters record the size parameter for X,Y and Z.

Delete the axis and go to the Action Editor and under the Globals Actor open the Size and set the End to the number of frames in your animation then, change X,Y and Z to the numbers recorded above.

What this does is reduce the area that Imagine will sample when it's calculating it's Oct-Tree at the start of each frame, thus it will be throwing less 'wasted' light rays. (Or at least that's how I understand it.)

I'm not 100% sure but on the Amiga version you only had to worry about the Camera and objects being inside the reduced area- light's were not affected.

It is also useful for certain effects, as you can animate the size of the Globals Actor. For instance you can have a Logo and have the Globals size scale so that at the start the logo is outside the 'box' and invisible, then as the 'box' increases in size, more and more of the logo becomes visible. Literally more and more of it appearing from nowhere as the animation proceeds.

Hope this helps.

All the Best,

Kevin.

Posted on: 2009/9/15 20:27
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Re: Raytrace - what are the best techniques for speedy tracing?
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@Johan: Multi-threading IFW? Now *that* would be cool! That's definitely on my wishlist

Posted on: 2009/9/15 21:21
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Re: Raytrace - what are the best techniques for speedy tracing?
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Hey Bill, thanks for taking the time to reply! I had to LOL when I read your suggestion re- setting up a render farm! I had exactly the same idea recently! I'm a bit of a PC enthusiast so I actually have a few spare P3 boxes lying around, but not much room to set them up...maybe in the future some time...if the Mrs lets me

I am using IFW 2.1.9 which I understand is the most recent update, and yes I noticed the dramatic improvement in raytrace times compared to IFD.

Yes, the images I've uploaded here are actual frames from the video. Since the output video is ultimately intended for youTube, I do them as 720p and most times I use VDub to do a 1/2 size reduction. But I never thought of turning off antialias in Imagine and then re-sizing the output. That's a great idea! VDub has a hi-quality plug-in to do this and should be able to do the entire uncompressed clip in one pass...definitely gonna try that one! Thanks Bill!

Posted on: 2009/9/15 21:50
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Re: Raytrace - what are the best techniques for speedy tracing?
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Cheers Kevin! You know, now that you mention it, I *do* remember something about setting the Global Size from the Amiga days...

Thanks for reminding me of this useful tip...I will do some test renders using that process and see if I can get some rigour around the actual time-saving. Boy, my ageing memory is really getting a workout tonight

Posted on: 2009/9/15 22:03
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