I swear I saw this subject come up here previously, but I can't seem to find it:

Can I go to my local paint store (or wherever) and get them to mix me the "proper" mix for chroma-key green? What would that mix be? Or, even better, is there an existing color within a popular, readily available brand that I can get?

Now, I know that techincally, any color can be keyed out, but it's my (limited) understanding that chroma green (or tech green, or whatever it's called) is a unique mix that is far away enough from hues found in most skin tones, or something like that. I could be completely wrong, though...

I know you can buy chroma green paint from video supply stores, but it is usally a little pricey. I'm looking for a more economical way to key.

I don't have any upcoming projects that involve keying, I'm just curious... and avoiding work...

Go to the paint store and get a whole pile of those sample cards with different shades of green.
Hang them where you intend to paint, with your lighting on, and shoot some video with your white-balance calibrated camera.

Load a frame of the video into your computer and look at it with something that will let you examine the RGB values of the pixels.

Find the shade of green that is as close as possible to g=255, r=0, b=0 as possible. If you're camera and lighting are good, you should be able to get at least as close as g > 200 and r,b < 60.

Take that paint sample back to the shop and have them mix up a batch for you.

Have fun.

So the magic mix is simply all green, with absolutely no red or blue? So, in theory, I could make a G->255 square in Photoshop, print it out, and take it to the paint store for them to match? (barring any discrepencies in the printout)

I was going to go to Kinkos soon with some P-shop files, for them to print out some warm balance cards for me; I guess I will have them print out a green screen sample for me as well...

Pick up a piece of chroma paper from a backdrop, take it into your local hardware store, and have them mix up a flat latex match.

Close enough if your not willing to pay the big bucks.

<<<-- Originally posted by John Britt : So the magic mix is simply all green, with absolutely no red or blue? So, in theory, I could make a G->255 square in Photoshop, print it out, and take it to the paint store for them to match? (barring any discrepencies in the printout)

I was going to go to Kinkos soon with some P-shop files, for them to print out some warm balance cards for me; I guess I will have them print out a green screen sample for me as well... -->>>

Just keep in mind that lighting and white balance also play a part in the final color captured by your camera.

Richard -- good idea, but I don't (as far as I know) have access to any sort of "proper" chroma reference, eg: backdrop paper, etc. (actually, I may have access via the University, but let's pretend I don't b/c A: I don't want to go to the trouble and B: someone in the future may have the same question and may search for this thread)

Nick -- good point. But what about the "proper" chroma green (like the spray paint you can buy from markertek)? Isn't that just a universal color that you would just have to work with as is?

John,
If you have access to a production house, they can usually provide you with a "chip" of paint or paper. Or, you can order a can spray "chroma" paint, and work from that. Or buy the smallest sample you can afford. Are you painting a big area?

I don't know if this will work or not but the book 'Digital Video for Dummies' says:

"... an effective ble screen can be built for less than $50. My favorite material for the purpose is blue plastic picnic-table covering (available at your local party-supply store) - it's cheap and effective..."

There is a thread here on it indeed:

http://www.dvinfo.net/conf/showthread.php?s=&threadid=6158

It has the Pantone numbers to use, not sure how correct it is.

Thanks, Rob. I believe that's the thread I was looking for. (I think I found that thread when searching; I guess I just didn't make it to the second page!)

I'm not sure about that Pantone number, either: using the various Pantone options in Photoshop, #354 looks much darker than the sample shown (via a link in that thread). Interestingly, a P-shop canvas colored using Nick's G=255 suggestion more closely matches the sample in that link, and looks more like traditional green screen. But this could be due to some sort of limitation in Photoshop re: the Pantone palette, I guess...

<<<-- Originally posted by John Britt : Richard -- Nick -- good point. But what about the "proper" chroma green (like the spray paint you can buy from markertek)? Isn't that just a universal color that you would just have to work with as is? -->>>
Keeping in mind that this color is intended for use with professional studio lamps, yeah that would be just fine.

The main thing is that "Color Difference Keying" is the primary calculation used for digitial color-based compositing these days. The math for this calculation is roughly Transparency = GREEN - MAX(BLUE, RED). A high very low red & blue channel values subjected from very high green channel values gives you lots of transparency on your greenscreen pixels.

This is never truely 100% transparent, so the software offers controls to manipulate and tune the result. You can typically get the screen to be transparent as long as the screen is SOME shade of green, but if there isn't a dramatic difference in the channel values, getting good detail in the edges of your matte becomes very challenging.

The more seperation that you can START with (between the value in the green channel vs the higher of the two others on your actual screen) as captured into the computer, the more range, control and detail you will have to work with at the edges of your composites.

Have fun.

The problem w/ taking it to Kinkos is that for the color print, they will charge too much (like $2 for a page or something?). Also, you don't know if they have all of their print profiles calibrated correctly. In addition, it will probably print w/ a CMYK process rather than an RGB color process, so the color will not be the same green that you are expecting. However, it may be close enough.

Still, it will be too much, price-wise.

You can get some chroma-green cloth from the Serious Magic web store for $20. You can use that, and if you want more, take it to a fabric store and look for a close enough match, or get some paint mixed up from the same.

Alex F

Alex -- Sorry... what I meant was that I would have Kinko's print out a small swatch for me to take to the paint store, not a whole backdrop's worth (which is what I think you thought I meant). I think it would be close enough for my purposes (and probably closer than my old Epson would do).

I will check out the Serious Magic store at some point as well. That's a very good suggestion. And like I said, I don't have any immediate projects requiring keying, this is more of an intellectal exercise/possible winter "fun" project.

Yes, I thought you meant an entire backdrop! :-)

Alex F

Save yourself the trouble and buy the vinyl chromakey paint for $40 bucks. You'll be happier.

http://shop.store.yahoo.com/cinemasupplies/chromkeyfab.html

I saw that someone above already mentioned this, but I went to the local party store and bought a roll or light green table cloth. It worked great. I wouldn't want to commit a studio or a room to green screen. The more important thing to the exact hue color is the consistancy in lighting. I didn't use it, but I know that FCP has a wave form monitor in it that you can use to see your consistancy. Another important thing in green screen is called "garbage matte". Learn how to do this as it's important

Walmart. Paint color Argula. $11.88 per gallon. Get it in flat, works great.

The paint is number 91322