In Scott Pilgrim VS The World there is this three frame sequence:
The second frame seems to be actually lit much more, not just made brighter by an After Effects adjustment layer.
How was this achieved? Is it a practical lighting effect? Was it shot in RAW and manipulated later?
This is most likely a practical effect accomplished with a photographic flash. It would just have to be fired on the action at the appropriate time. Photographic flashes are extremely fast firing and completely discharge in a very small fraction of a second. Since exposure is a cumulative effect, the majority of the exposure can be accomplished in a fraction of the time the shutter is open for capturing the frame.
This is actually how a particular type of high speed photography works. In a dark room, the shutter can simply be left open and the exposure occurs during the extremely fast flash, thus achieving a shutter speed that would otherwise not be possible with the camera.
This is a similar kind of thing, but done in a lit seen to give the one frame extra lighting. The additional highlighting on the shirt of the guy doing the punching is also indicative of the use of a photographic flash or strobe as the lighting on his shirt is completely different from the previous frame and the pattern of light seems to indicate an intensely bright light source (probably a fairly minimally diffused flash or strobe).
This is most likely not a practical effect. In order to achieve this effect practically, one would need a light that is sync'd to the frame rate of the camera to turn on for 1/24 (depending on the framerate) of a second. It sounds...impractical (word jokes!).
You can easily isolate a frame in After Effects by converting you time line to frame rate time signature as opposed to seconds.
Alternatively, you can use the hotkey (ctrl + right/left arrow) to create an animated color correction to do whatever you want. In this case, you would find the brightness/contrast effect, place it on your footage, press the animation icon on the effect, go to the spot you want to be bright, ctrl+right arrow back one frame, create a key frame, crtl+left arrow two frames forward, and create another key frame. You back up one keyframe to where you want the effect to be, crank the brightness and bang, your effect is done. Quite simple.
To answer your question about RAW, it was likely shot in RAW, but that has no impact on how this effect was achieved. You can do the same with heavily compressed h.264 footage.
