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Animated Snow Trails

9 September 2004 31,392 views No Comment

Animated Snow Trails continued…
Processing The Image Sequence

We’re now going to process the rendered image sequence in Digital Fusion

Add two Loaders (LD) to a new flow and load the rendered image sequence into both of them. For one of the loaders, set Clip Time Start and Clip Time End to 0, and set Extend First Frame to 180. This will ensure that that loader only ever outputs the first frame of the image sequence.

Add a Channel Booleans (Bol) and set the background to the main Loader, and the foreground to the single frame Loader. Change the settings of the Channel Booleans tool to:

Operation:    Subtract
To Red:       Red FG
To Green:     Green FG
To Blue:      Blue FG
To Alpha:     Do Nothing

Digital Fusion Flow

You’re probably asking what’s going on here. Well, all we’re doing is subtracting the first frame of the image sequence (which doesn’t contain the ball), from each frame of the rest of the sequence. Take a look at the image below for a more visual explanation:

Image maths!

The cool thing about this, is that we’re left with only the displacement due to the ball. What’s more (and this a fairly subtle point), since we’ve subtracted the displacement of the surface from the entire image (including from where the ball is), the image represents the difference in height between the lowest point on the ball and the snow surface, i.e. we can apply this to our displaced snow surface and it will deform to perfectly accomodate the ball.

Since this displacement map will work on our height varying snow surface, we’ve already satisfied the fourth point of the problem that I originally stated on page 1 of this tutorial.

The next page shows you how to turn the output of this flow into an animated snow trail displacement map.

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