Cinematography Mailing List - CML

Replacing Image On A TV Screen


I might have to shoot some shots (in 35mm) of a blank TV screen where the image will be added in post later (I am not going back to film). Any suggestions on simple ways to make it easier to matte in a picture into the TV screen?

Is the standard "blue field" that some VCR's produce adequate for generating a chroma-key or does it have to be a true bluescreen color? Do I have to get rid of any roll bars or can that be dealt with by the person doing the chroma key? Would a white screen be better (for a simple luminance key)? Do I still have to worry about the roll bar? (I'm trying to avoid the whole sync-box issue & costs if I'm not really going to be filming true images off of the TV.)

David Mullen Cinematographer / L.A.

We have had very good results from using fluorescent blue and green paper . You can get it at art supply stores. It is thin (not much thicker than typing paper or thin gift-wrapping paper) and can easily be dressed in to the screen and tacked down with a bit of spray adhesive. The color is so saturated that ambient light will often do just fine. The only problem is that since it is not covered with glass, the reflections that you might want to see in the screen won't be there.

Depending on the shot, you might want to use generated blue or green video, which would give you the light kicks on the front of the screen, but, as you mentioned, there is the sync issue.

Do you need to sync?

Well, yes and depends on the tools available to the post house. If it is a moving shot and they can easily track it and the shot of the screen is clean, the rollbar may not be a problem, depending on where it is and how fast it is moving and etc etc ..I wish I could be more helpful - the devil is in the details. Does it have to be a sync sound 24 fps shot? Can you narrow your shutter to avoid the rollbar and just keep the rollbar in the viewfinder? If you can, generated blue or green might be the way to go...if the light kicks in the screen look right, and if the camera is moving, having them in the right place will help sell the shot. If they are missing or have to be tracked in by hand it may not look as good. A high-con might work fine, but may be problematic if you have action crossing the screen...and it really depends on the tools available to the post house (and their strengths and weaknesses.) Sorry to sound so wishy-washy

Mark H. Weingartner

Lighting and VFX for Motion Pictures

I was on a shoot a while back where they carefully pasted green fabric (felt?) on the tv screen for compositing later. I didn't see the final product but is seemed like should have worked.

Steve Smith AC/LA

>Is the standard "blue field" that some VCR's produce adequate for generating a >chroma-key or does it have to be a true bluescreen color? Do I have to get rid of any >roll bars or can that be dealt with by the person doing the chroma key?

I just did a shot like this over the weekend for a music video and the editor said that the blue was perfect. He did ask me beforehand to adjust the brightness of the TV as well as raise the chroma so he'd have a nice, rich blue to key off of. He said not to worry about the flicker and apparently there was no problem although I haven't seen the finished piece yet. I did do my best to try to keep hot spot reflections off the screen, which was no easy task.

Mitch Gross

>I was on a shoot a while back where they carefully pasted green fabric (felt?) on the >tv screen for compositing later. I didn't see the final product but is seemed like >should have worked.

All of these suggestions are good, but only if the shot is moving constantly and/or has many foreground crosses. Even in that case, I would most often shoot with a blank screen, provided the frame of the picture tube itself is visible (as a matter of fact, that's what I have done many times). The corners of the tv set itself (as well as many other things in the shot) can serve as tracking points to recover the camera moves, and by shooting with a blank screen you have natural reflections to use in the composite (even the reflection of the camera crew is a good, usable reflection when blurred). You also avoid any blue or green (or whatever) spill between the picture tube and the surrounding frame, as well as on anything close to it. Foreground crosses are easily rotoscoped, provided they don't plant themselves in front of the monitor and move around for an extended length of time (and/or don't have their hair in the matte area). Just be sure to avoid significant perspective shifts.

All of the effort we make to create blue or green matte areas is often much ado about nothing. With today's software based compositing tools, it's often much simpler to create a matte in post (by rotoscoping) than to try and pull a less-than-perfect green or blue matte and clean up the resulting spill areas. Particularly when the object being matted is static and there are usable tracking points in the shot (which there almost always are on any decently dressed set). Often the green or blue material is simply treated as a visual guide by the compositor for creating rotoed mattes.

Mike Most

We just did a similar shoot to the one Mitch described with potentially horrible results. Seems to me if the editor is telling you not to worry about the flicker or roll bars then he is expecting to do something other than bluescreening the image - which is what we ended up doing.

The TV was adjust so that there was a nice, rich blue screen, the only problem was that it photographed quite differently. While it was blue, we somehow miss calculated and the image on the screen was rather dark. As luck would have it, the image was shot where the TV was almost perpendicular with the shot angle. All that had to be done in post was overlay the TV screen with the video using After Effects.

I'm now wondering how you would do bluescreening of an image that is flickering as Mitch described?

-JR Allen

If using the actual blue from the TV tube, would that not become a rather strong blue light source that would spill on anything close to it and reflect off furniture, glass anything else in the room???

Daniel Villeneuve, c.s.c.

Directeur-Photo, Director of Photography Montréal, Canada

That's pretty much been my experience. The decorative mask around the tube is usually significantly polluted.


Bob Kertesz BlueScreen LLC

But that can be useful if you want a realistic interactive glow around the TV - or bouncing onto anything near. A TV does act as a light source, after all. One case where spill helps, although it's useful if the spill is darker than the screen itself so you can seperate the image and it's glow/reflection. Needs care to make this work properly.

My experience of comping inserts with un-sunc blue feed on TVs (24fps shooting NTSC - obviously no proper shutter angle compensation) was a nightmare - the roll bar made the screens useless, and the shear when the camera panned was a pig to remove, and got in the way of tracking the replacement images into the move. Added to this there were tracking grids on the feed to the TVs which sheared and rolled as well and had to be removed!

I've had much less hassle with unlit green or blue cards in dummy monitors. The ideal for me would be a translucent backlit green or blue in a dummy TV behind a real glass screen, so you can get reflections on the screen (although not always desirable), and some degree of glow. If nothing passes in front of the screen and you don't want interactive glow, there's no reason to use blue or green at all - any moves need to be tracked in anyway, so replacing the whole thing should not be a problem. Just leave the TV turned off and make life simpler!

Tom Debenham


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