On Mon, 17 Nov 2003 05:58:45 GMT, wrote:
We currently shoot pics of all our product on a white, light table to make it easy to cut away the background and use the shots in printed catalogues.
Problem is that the light table is not so good any more… it’s getting a little scratched an dirty and we still have some issues with shadows when it comes to cutting the pictures out.
Is anyone doing anything smarter than all that? I’m thinking Star Wars and Blue Screen backgrounds that can be eliminated with the click of a button?
The idea of the blue (or green, etc) screen is that the colour is something that doesn’t appear in the subject matter of the shot. Thus, when you select that colour, you’re not inadvertently selecting anything that appears in the foreground.
Occasionally, particulaly with a junior weatherman, you’ll spot a hole in the chest of the weatherman on television as he is pointing at the overlayed weather map behind him. That’s because he ended up wearing a tie which had colours similar to the alpha they were using for the background. Video alpha more or less works on a similar principle to a fiilm bluescreen, though it is processed in realtime via video circuitry.
Since even with a digitial camera, the background is going to have some "noise" in it (take a shot and zoom way in), you have to contend with a "similar colours" selection anyway, though probably only to about 3% or so.
The trick with a bluescreen is to thoroughly illuminate the bluescreen from a point behind your subject matter with directional lighting, so that shadows are not cast onto the bluescreen from your foreground illumination, while at the same time, the foreground isn’t illuminated from behind. If you don’t do this properly, you’ll have a great number of blue-ish hues to mask around the edges of your subject matter..
It might also help to note that to minimize light coming in at the subject from different angles, such photography is best done in a draped or blackwall room (i.e. where the surroundings do not reflect significant light back upon the subject).
As for your use of a light table – you certainly don’t want to bring light up from your table onto your subject matter, since you can’t simply mask on that light colour – you’ll have an obvious halo around your subject, which is the same reason for illuminating the bluescreen with directional lamps from behind the subject matter.
BTW, for light tables/boxes, you should consider heading to a plastics shop and getting a replacement top insert. Just record the dimensions of the original, and reorder when necessary. Alternatley (and this depends on your optical needs), you might get some untinted plate glass to overlay on the top. Glass is remarkably scratch resistant (certainly much more so than plastic), so what you end up with is a semi-opaque plastic sheet which diffuses the light, and a glass sheet above that for hardness and protection.
I imagine the production snippets available on some DVDvideos these days should include some minimal footage of a blue or green screen layout from a productions POV, instead of merely through the camera filming the subject.
You might also get some additional pointers by checking forums frequented by video production people, such as those for Adobe Premiere, since when you’re working with thousands of frames of video, you want the screen to work without a lot of manual tweaking.
