Minus-green and minus-blue are old tricks. In the old days you could often spot a yellow cast when cameras weren't painted quite right. It's also important for the on-camera folks to dress correctly so none of their wardrobe vanishes. I'm amazed at how many of them don't know this. The lighting on the background was always the most critical thing in my experience. As even as possible, and as shadow-free as possible. We frequently got away with greens or blues that weren't quite right if they were lit well enough. That was with the stone-age cameras of my youth. I would hope things are not as critical now. Then again, we used a green Insta-Key drop in Atlanta years ago, and I remember that Harry Calas' eyes were so green that we couldn't help it that they keyed out. Talk about a weird effect. mg

[quote="scottgfx"]Does anyone have any frame grabs of their green wall that I could see? I could also post my samples if anyone is interested in looking.[/quote] Since you asked, I figured I'd grab a few this AM. We had the blue wall down this morning, but you can see the green. Lighting is the same for both walls. If you want some grabs the green wall, I can easily get those too. Helping out where I can, Don TD - Director KXTV-Sacramento

[quote="Mike Cumbo"]Scott, are there any gels or any diffusion material on the lights? If so, have they ever been replaced? Those items will change with time.[/quote] Good point. I've seen diffusion become brittle and yellow over time. The guy they contract with to do the lighting was here back in October. I know they worked on the wall. I'll have to ask the production manager about what was changed. Most of the instruments in our studio are now florescent, including the main lights on the CK wall. I would imagine that there is still a lot of UV (if not more) that will degrade plastic diffusion material.

Scott, are there any gels or any diffusion material on the lights? If so, have they ever been replaced? Those items will change with time.

[quote="sahonen"]It should be a straight, flat line all the way across. It it's fuzzy or it dips at all, that's an indication of uneven lighting.[/quote] Bringing out the shadow was one of the things I wanted to do, but as you may have guessed, the lighting is not even. There is even a texture to the wall that starts to become visible. The other issue is that the talent is standing too close to the wall. They want to be able to touch the wall. The location of the wall is another problem. It's in a corner of the studio and there isn't much room to hang instruments. I'll at least attempt to tackle the issue of the color of the wall. :)

If I have a good keyer with good color suppression, I make the key fairly soft. Instead of trying to get rid of the shadow behind the talent, I just try and make it look as natural as possible. The closer I can get to it looking like the talent is standing in front of a physical wall with a weather map on it, the better, and part of making it look real is getting the shadow right. The big ugly black blobs you get with really hard keys are unnatural and distracting. While you have the waveform monitor/vectorscope out, see if you can click the waveform monitor into luminance-only mode (might be labelled low-pass or chroma suppress). It should be a straight, flat line all the way across. It it's fuzzy or it dips at all, that's an indication of uneven lighting. [quote]A problem I've run into is that the camera setup was done with an LCD monitor and without the benefit of an HD CRT.[/quote] Now that LCD and multiview monitor walls are becoming the rage, truck/control room designers are forgetting that you still need at least one good CRT in the truck/control room for shading cameras. LCDs don't cut it. No matter how much they've improved in the last few years they still don't touch the color accuracy of a CRT. The Big Ten Network trucks don't have any CRTs in them at all, and I've heard it's a nightmare for video.

Thank you for the input everyone. The Kahuna keyer has color suppression features, so I don't know if gels are really necessary, but I'll look into "minus green". I hadn't heard of that one. I remember people trying magenta filters a long time ago, and they just ended up with purple fringes. :) Good point about the vectorscope. Our camera CCU station does have a CRT. The last person to set the cameras up was probably the Ikegami guy that installed them back in October. I did note that the green is not a dot, but a bit of elongated fuzz. So the hue is fairly true, but is varies a lot in saturation. Does anyone have any frame grabs of their green wall that I could see? I could also post my samples if anyone is interested in looking. Thanks again! Scott Thomas

A problem I've run into is that the camera setup was done with an LCD monitor and without the benefit of an HD CRT. It was hard enough trying to get the large plasma multi-views matched with the LCD at the CCU station. When we did a color pick on the switcher for the chroma key, the picked color on the switcher GUI did not look like the color on the LCD or plasmas. We rented a broadcast HD CRT and there was a huge difference between that and the LCD. Now the cameras and chroma keys look much better. Irv

Minus Green on your back light can work wonders too. Go with the lowest intensity that works and you shouldn't see any kind of a purple rim. Probably 1/4 or 1/2 will do the trick. -Kim

For the best starting point, it's tough to beat Ultimatte paint. But whatever paint you decide on, it should appear on a vectorscope as a solid dot...a fuzzy dot means that the color is not pure - your keyer should still be able to handle it, but it'll mean more tweaks. Other things can affect the key, such as camera shading and most importantly lighting: I've seen a lot of LD's try to "warm up" the talent by the addition of amber gels...this often tends to do little more than make it tougher to do a clean key. Based on what you're saying, it almost sounds like you've got one of those weather folks who likes to "touch" the map. Depending on the lighting, this causes deep shadows on the wall - a lack of light in the wall equals no color rendition which equals an impossible chroma keying situation, regardless of the switcher's ability. One way to fix this is to add top & side lights to keep more light on the wall. Another way to ofteb fix this is to simply have your talent step away from the wall. Using a Chimera or other diffuse light will also gradiate the shadows and give the chroma keyer a fighting chance.