I'm shooting a music video for my house mate and as part of my uni course. For one part I want to have the video of him singing wash away into the animated river which forms the main content of the video.
My only thought was to print out the last frame and paint it onto some white acrylic in black and film it as I drip water down it then use this as the matte for the animated water colour. But I wanted to know if anyone knew a clever way i could achieve something similar using after effects. Maybe a gradient wipe or something.
No matter what you are going to need quite a bit of post work to make that look good.
IMO filming real assets is always better than faking them in AE.
As far as faking it (or for compositing the filmed drips), I would look into the Caustics effect. It won't simulate the drips, but it will add a realistic water refraction effect that will help it transition into the river. Then again, it depends on how the river is animated, and what kind of look you're going for.
If all you are looking for is the shape of the drips, then you could make a matte using Mr. Mercury, but it's a pretty lame effect with minimal controls.
Also, if I'm following you right, you could film the drip transition in high contrast, use it as a matte, and composite it with the matte you're currently using. That way you won't have to repaint the last frame, or worry about it matching.
I would try to shoot paint dripping on glass in front of chroma. Get as many shots as you can, then key them out and morph your image in these.
Here's a quick way of morphing in AE with no extra plugins:
Use Mesh Warp.
Set 2 layers in a AE comp- the "morph from" layer on top of the "morph to" layer.
Start on the layer you want to morph from- apply Mesh Warp and set keyframe. Move 8 to 15 frames (or as many as you need your morph to be) and change transparency to 50% so that you can see the layer under. Use the mesh warp to distort the features of the top layer to match those of the bottom layer.
Apply Mesh Warp to bottom layer and set keyframe at the end of the transition. Go back to the beginning of the transition and use the Mesh Warp to distort the bottom layer to match the top one's features.
Set transparency keyframes to animate the top layers opacity from 100% to 0 for the length of the morph.
That's basically it.
Hope it helps.
Thanks for the advice, i was leaning towards the idea of filming the assets and then using some after effects wizardry to blend it all together, this seems like the perfect solution. Had a look a mr Mercury too, very like the particle (world?) effect, may not be a useful for that instance but using it helped me with the animation of the river (by increasing the particle size to form a undulating mass) so thanks.