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Orbaz Technologies Forum Index » Orbaz News » Particle Flow and Particle Flow Tools in movies
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Particle Flow and Particle Flow Tools in movies
PostPosted: Sun Jul 09, 2006 9:22 pm Reply with quote
Oleg
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Joined: 26 Sep 2004
Posts: 5701
Location: The Hundredth Town, USA




Particle Flow and Particle Flow Tools were used in production of Memoirs of a Geisha.

Adam Watkins, 3D Lead, tells us about it:

...my favorite example from the show is what we called the "spring to winter" sequence, which marks the major transition of Sayuri from child to a young woman/geisha.

In the beginning of of the sequence cg cherry blossoms were used to augment real cherry blossoms in the plate (a subtle effect). Then the sequence transitions to winter (several years later) with a very wide shot of 1930's Kyoto - integrating the California set with a huge multi-layered digital matte painting by Robert Stromberg, and layers upon layers upon layers of cg particle flow snow!

The snowflakes had to match exactly with practical snow that comes much later in the shot and for this the Camera Culling and Camera IMBlur operators were invaluable. It let me put an enormous amount of flakes only where I needed them, and dial in motion blur to what the practical flakes were doing. The Box#1 group tools were incredibly important to this process - the grouping functionality let me trigger the different patches of snow the camera had to travel through and let me 'kill' the occasional errant flake that strayed right in the centre of the shot.

Towards the end of the shot where we see the actress closing the house window, what isn't obvious is that a good chunk of the left hand side of the house has been entirely replaced! In the plate a practical flake actually landed and stuck to the middle of the lens, hiding everything behind it. So I recreated the side of the building, and then used particle flow to place CG snow over the top of it, matching exactly the motions of the practical snow around it. It took me less than an afternoon to do and I got the perfect result first time.

All artists that use Particle Flow should definitely get the other tools too - they paid for themselves on the very first shot I used them on!







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Particle Flow Tools in "The Ten Commandments"
PostPosted: Tue Aug 22, 2006 9:41 pm Reply with quote
Oleg
Site Admin
Joined: 26 Sep 2004
Posts: 5701
Location: The Hundredth Town, USA




Biblical times and state-of-the-art particle systems – what can link them together? Laszlo Sebo explains:

"The Hallmark miniseries The Ten Commandments followed the story of Moses from his childhood all the way to finding the Promised Land. Over the course of approximately 4 hours, the episodes had about 230 CG effects shots, of which the biggest challenge for our little team of CG FX artists was recreating the Red Sea opening up. The sequence consisted of over 30 shots of ocean surfaces, both close-ups and distant background shots.

Animation Video #1 (1.26 MB)

We only had a limited time to develop a look that matched the artistic vision of the production and create a pipeline with which we could make all the shots with a team of only 4-5 people. We tried to use the best of everything, so our Maya team created the animated ocean surfaces with different cloth simulation tools, and parallel, we used Particle Flow and PFTools:Box#3 for all the particle effects on and around the water, like foam, water spraying off the ocean, dust being kicked up, the general atmosphere etc. On average, each shot had about 12 ocean passes and 16 particle passes rendered. Some shots more, some less.



Without the huge control that Box#3 gave us over particle behavior and the speed optimizations that it has when working with lots of particles and reacting to animated regular objects, we could have never finished the project. I, as a CG FX Supervisor, pre-created a Particle Flow network for each of the main passes, which were then hand fitted to the particular shot that we had to work on, creating a rough overall particular motion, which we could then extend with additional more detailed particle passes later on if needed.

Most particle passes were highly dependent on the motion of the ocean surface, so I created flows where particle generation and the forces applied to the particles were based on different surface characteristics, like local acceleration or tension. Acceleration was easily sampled, but for tension sampling we had to create a shader that rendered a tension-like gradient to any surface it was applied to. We then baked this shader into the sea surface as bitmap textures, which were then sampled by PFlow. This method worked for some of the shots, but some shots had way too big sea surfaces to allow interactive particle creation. For those bigger shots, we hand animated low-poly "emitter" cage surfaces around the wavefronts moving upwards as the godly force was pushing.

Animation Video #2 (2.11 MB)

Some of the "hero" shots needed fine tuned atmospheric like, yet particular spray passes. For that, I created a PFlow Data Operator that sampled the particle density around each particle in the direction of the light source. Based on the density and user-set parameters, the operator would assign a UVW value to the particle, which was then used to sample a regular gradient ramp map. So simply put, particles that were surrounded by lots of other particles became darker, while particles separated from the main chunks were lighter. This gave a very dense, cloudy look to the particle mass that had sprays breaking off it.

Working with Box#3 was like having total control. With the Disk Cache operators we could also go crazy with particle counts, and still get nicely multi-pass motion-blurred renders. We just pre-cached everything, and then sent the system to render on the farm, no extra calculation was needed."

Animation Video #3 (7.47 MB)
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Particle Flow and Particle Flow Tools in movies
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