creating slow motion camera flash effect
I have a footage of a person where I want to make a camera flash on top of it. The camera flash I'm after is not just a white transition but rather a slow motion flash effect. (just like the one in Cinderella Man when he's boxing in the ring or The Aviator. something surreal with particles and depth). I tried to put a transition that devolves to white with camera flash sound. but it was pretty flat and realistically fake.
I'd appreciate any suggestions or help.
The movies you mention actually used cameras that could shoot at a very high frame rate. The light falling on the characters is real, with real shadows and highlights.
You could attempt the same thing with prerendered slo-mo footage, but you would have to be very careful to cut masks for the duplicated layer on top, trimmed to just one frame or two (the flash frame) in order to make the highlights and shadows look real.
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA
There are a couple of ways to go about this. You can't just add an overall "whiteness" to the image as it will not take into account the geometry of any of the subjects relative to the light flash.
For either method, you'll want to be working in 32 bit linear.
Method one (exposure with manual masks):
The most straight forward approach is simply to use masks and the exposure plug in, and some artistic judgement. If the flashes are short enough, this method works quite well.
1) Duplicate your footage layer (or create an adjustment layer) and add the EXPOSURE plug in to the new layer.
2) Set the exposure to around up 3 stops or so (you will likely adjust this later to get the look and feel you want)
3) On the new layer, create masks around the areas of object surfaces that face the flash. Use plenty of individual masks so that you can adjust the opacity of each, depending on its distance and angle to the flash.
4) Feather and adjust the opacity of each mask to get the right look. Add additional masks over masks to subtract, or add more in areas of complex geometry (like faces). For instance, use a narrow mask for hair above the scalp to give it back-light glow.
This process will take the "flatness" out of the flashes, and give them a more natural feel.
Method two (3D track and scene build for lighting/shadow pass):
If the scene needs a lot of relighting effects, then a second (and more involved) method is to track the scene using a 3D tracker such as PF Track. In that tracker define the various objects, and track objects and export to a 3D program such as Maya.
Build a replica of the scene - but the level of detail is not that critical - no need for texture maps, everything can be a simple grey - though you will want to alter specularity for shiny objects vs dull ones. leave out distant objects or objects that won't be affected by the re lighting effects.
Use the object tracking/mocap data from PFTrack to get all the subjects in the right place, moving correctly, etc.
Place lights in this scene where you want the relighting to occur, and animate the lights to flash (or whatever) over the period you want.
Render this scene out as a single pass using no ambient light, only the re-lighting lights(s).
Now you have a greyscale image of the scene's relighting highlights and shadows. Do the frist two steps from method one above - duplicate the footage and add the exposure plug in etc - then use the new greyscale image of the relighting effect as a luma key on the layer with the boosted exposure.
While this second method is obviously more involved, if you need to add lighting effects after the actual shoot, and those effects are going to play for more than a few frames, then this method may be worth the extra time in setup.
An additional advantage is that this method allows you to add in atmospheric effects, like smoke or haze, to show the light rays and further integrate them into the scene. In this case you would do an additional haze pass, where a particle system smoke or haze was added to the scene, then all of the in-scene objects would be set to render as pure black, no reflectance, so they act only as obfuscation objects and shadow casters. In this case, ambient and source lights may need to be added to match the actual scene - in this case you may want to use channel lighting to have control in the final comp.
The resulting smoke/haze pass can then be dropped on top of the layer stack in additive mode (assuming you are doing all this work in 32 bit linear) to add in the light rays through smoke/haze.
Thanks heaps for the replies!