boundary treatment when extracting objects in front of blue screen?

If I have a person shot against a blue screen, how can I extract the person to put in front of other background?

The simplest solution would be to use magic wand to select the blue background, inverse, then copy the person.

However, there is a problem at the boundaries. Let’s say this person is wearing white clothing. At the boundary of the white clothing and the blue background, some pixels are a mixture of white and blue color. If these pixels are included, there will be a faint ring of blue color around the person. If these pixels are excluded, let’s say by contracting the selection, then part of the person is lost. Even if I feather the selection, this problem still exists.

What is the solution?

peter wrote:

If I have a person shot against a blue screen, how can I extract the person
to put in front of other background?

The simplest solution would be to use magic wand to select the blue background, inverse, then copy the person.

However, there is a problem at the boundaries. Let’s say this person is wearing white clothing. At the boundary of the white clothing and the blue
background, some pixels are a mixture of white and blue color. If these pixels are included, there will be a faint ring of blue color around the person. If these pixels are excluded, let’s say by contracting the selection, then part of the person is lost. Even if I feather the selection,
this problem still exists.

What is the solution?

use a high angled backlight with a warm gel, which will
generate a cleaner mask as well as getting rid of the fringe.

Mike Russell
www.curvemeister.com/forum/

This is a well known problem with blue screening. If you have control during the shoot, use a high angled backlight with a warm gel, which will generate a cleaner mask as well as getting rid of the fringe.

If you are dealing with images after the fact, there are a variety of ways to deal with it, as Ron says. You can hit the blue areas with the sponge in desaturate mode, or knock back the blue with curves, Hue Sat, select the area using the matte and use defringe, or a variety of other tools in Photoshop.

Mike Russell wrote:

use a high angled backlight with a warm gel, which will
generate a cleaner mask as well as getting rid of the fringe.

Mike Russell
www.curvemeister.com/forum/

Hi Mike,
Why does this work?

I am not Mike, but I am a photographer. Picture the extra light coming from behind the subject, out of view of the camera lens, and therefore it is not illuminating the blue background. With a warming filter, it creates a clean color contrast at the edges of the subject that would otherwise be commingled (via hue and luminosity) with the blue background.