blue/green screens

Dan Margulis <76270.1033@...>

Andrew Engelhardt writes,

just wondering if anyone has any experience shooting or dealing with
images that have been shot against a blue screen? We have to try to
facilitate a high volume of single product images with clipping paths in a
fairly fast turn-around time and we're looking at how to speed up the
process of getting paths on everything. We're hoping that the blue or green
screen background might help either Photoshop or another program like Mask
Pro with creating a path quickly and accurately. These are files that will
be repurposed for a bunch of different uses from all kinds of printing
conditions to web use, thus the paths on just about everything. The only
problem we can think of so far is when the colour of the product is close
that of the background.>>

Having the background in a contrasting color is definitely helpful, however
AFAIK there isn't a way of completely eliminating the human factor. If it's
a simple shape probably nothing is going to be faster than the pen tool. If
complex, and if there are a *lot* of such images, AND if the blue color is
fairly constant and fairly pronounced, then I'd consider a script that did
the following:

1) Make copy of image

2) Convert copy to LAB.

3) Apply drastic curves to A and B channels, making them much steeper and
moving them to the right (i.e. magenta-yellow direction). This will make
the background a brilliant blue and make give everything else a red cast.

4) Virtually wipe out the L channel by reducing the black point to about

6) Return copy to RGB.

7) Move the shadow point of the RGB master curve so far as to restore the
darkness of the original image that was wiped out by Step 4. This will
insure enormous edge contrast in color.

8) Allow operator to click a representative portion of background. Select
by Color Range, Fuzziness 200.

9) Save Selection as a separate document.

10) Discard the altered copy of the original.

The saved selection is going to be rather close to a mask and it will be
easy for the operator to edit out extraneous parts.

If I were distributing these images, I'd consider doing so with masks, not
clipping paths. Making efficient clipping paths is a lot of work; if the
user needs a clipping path and already has a mask, the path is easily

Dan Margulis