Keying through a window at DVinfo.net

Justine Haupt · March 25th, 2007, 07:10 PM

I searched for but couldn't find any information at all on this.

How would one pull a matte from a green screen that is behind a window or windshield while maintaining a sense of the presence of the window (like reflections, fingerprints, dirt, etc).

I don't have a specific project in mind that required this, but it's something I've always wondered in case it comes up.

I've had some luck doing this a way I concocted. I shot the talent looking out her apartment window, which was essentially black outside, but with a backlight shining in from the outside of the window, out of frame (kind of a hair light, to reveal the marks on the glass).

I than matted out the window manually (by drawing the matte for each frame), and than overlayed a copy of the window on top of itself with the opacity lowered enough so that you could see the window, and what I had put outside it, too.

It worked pretty well, but there obviously must be an easier way. Could someone explain?

Here's a frame to show what I tried. Remember, I didn't use a green/blue screen, so this was extremely time consuming (and not perfect, though the attached frame is one of the best ones from the clip)

James Huenergardt · March 27th, 2007, 11:29 PM

Actually, depending on how long the shot is, if you can roto it, do that instead of shooting on a greenscreen.

The greenscreen will add a green or blue (depending on the color screen you used) hue to your shot, and what you did is actually a better way to do it.

Read Stu Maschwitz's book called "The DV Rebel's Guide" and you'll learn a lot from one of the guys who does this for a living.

Hope it helps,

Jim

Alan James · March 28th, 2007, 12:50 AM

I would actually go about green screening it. If you can get the green outside the window near perfectly lit (not to hard on a set) then it should be a snap. Keylight in After Effects will take out the green and leave the other colors.

Usually this causes a problem cause it will remove all the green but leave shadows in your green screen if there are any, but in this case its the solution.

As far as having a green hue, just add a spill suppressor. Problem solved.

Its all about getting a good color green outside and thats all.

Conor Ryan · March 28th, 2007, 07:31 AM

Like Alan says, Keylight will do a good job of holding reflections if your greenscreen it.

Another technique, that is a bit trickier, but can yield good results is removing the window. Set up a greenscreen outside, and a mirror-image camera (same distance from the window as your main camera, same angle from the window pane, just flipped, so it's outside). Shoot, then do your greenscreen and composite the mirror-image over the background.

This is limited, but can help you get good results. It usually means you can't do big camera moves, and you have to be very careful to line up the two cameras, and to get the compositing done right.

Justine Haupt · April 9th, 2007, 03:57 PM

Thank you everyone for the responses -- I was hoping there was one sure-fire method I was just missing. I guess I will have to experiment.

March 25th, 2007, 07:10 PM	#1
Justine Haupt Major Player Join Date: Oct 2005 Location: Long Island, NY Posts: 208	Keying through a window I searched for but couldn't find any information at all on this. How would one pull a matte from a green screen that is behind a window or windshield while maintaining a sense of the presence of the window (like reflections, fingerprints, dirt, etc). I don't have a specific project in mind that required this, but it's something I've always wondered in case it comes up. I've had some luck doing this a way I concocted. I shot the talent looking out her apartment window, which was essentially black outside, but with a backlight shining in from the outside of the window, out of frame (kind of a hair light, to reveal the marks on the glass). I than matted out the window manually (by drawing the matte for each frame), and than overlayed a copy of the window on top of itself with the opacity lowered enough so that you could see the window, and what I had put outside it, too. It worked pretty well, but there obviously must be an easier way. Could someone explain? Here's a frame to show what I tried. Remember, I didn't use a green/blue screen, so this was extremely time consuming (and not perfect, though the attached frame is one of the best ones from the clip) Attached Thumbnails __________________ ~Justine "We are the music makers, and we are the dreamers of dreams" -Arthur O'Shaunessey (as quoted by Willy Wonka)

April 9th, 2007, 03:57 PM	#5
Justine Haupt Major Player Join Date: Oct 2005 Location: Long Island, NY Posts: 208	Thank you everyone for the responses -- I was hoping there was one sure-fire method I was just missing. I guess I will have to experiment. __________________ ~Justine "We are the music makers, and we are the dreamers of dreams" -Arthur O'Shaunessey (as quoted by Willy Wonka)

March 27th, 2007, 11:29 PM	#2
James Huenergardt Major Player Join Date: Nov 2005 Location: Chehalis, WA Posts: 513	Actually, depending on how long the shot is, if you can roto it, do that instead of shooting on a greenscreen. The greenscreen will add a green or blue (depending on the color screen you used) hue to your shot, and what you did is actually a better way to do it. Read Stu Maschwitz's book called "The DV Rebel's Guide" and you'll learn a lot from one of the guys who does this for a living. Hope it helps, Jim

March 28th, 2007, 12:50 AM	#3
Alan James Regular Crew Join Date: Jul 2006 Location: Tampa, Florida Posts: 261	I would actually go about green screening it. If you can get the green outside the window near perfectly lit (not to hard on a set) then it should be a snap. Keylight in After Effects will take out the green and leave the other colors. Usually this causes a problem cause it will remove all the green but leave shadows in your green screen if there are any, but in this case its the solution. As far as having a green hue, just add a spill suppressor. Problem solved. Its all about getting a good color green outside and thats all.

March 28th, 2007, 07:31 AM	#4
Conor Ryan Regular Crew Join Date: Oct 2004 Location: Dublin, Ireland Posts: 67	Like Alan says, Keylight will do a good job of holding reflections if your greenscreen it. Another technique, that is a bit trickier, but can yield good results is removing the window. Set up a greenscreen outside, and a mirror-image camera (same distance from the window as your main camera, same angle from the window pane, just flipped, so it's outside). Shoot, then do your greenscreen and composite the mirror-image over the background. This is limited, but can help you get good results. It usually means you can't do big camera moves, and you have to be very careful to line up the two cameras, and to get the compositing done right.