Chroma Key Green Screen always unwantedly removes green hues

[Justinec101]

Ok I've run into this twice now. Even when using "Pure Green Screen" (with green at 255) it always causes turquoise hues to turn pure blue. Even when I adjust the high/low thresholds all over the place. It does this with yellow to a degree, but not as bad as it is with shades of blue. Here's an example

and here it is after applying the chroma key filter (with an orange backdrop on the bottom layer)

No matter what I do, I can not get it to go back to a light blue shade. Why is this happening only with blue and not yellow or orange? Like I said, it happens a bit with yellow, but orange is almost entirely unaffected.

 

[David Jimerson]

That's because there's a lot of green in turquoise.

 

[Justinec101]

I understand that. There is also a lot of green in yellow and orange. In fact the yellow splotch in my picture has more green in it than the turquoise splotch does. What I'm asking is why does "pure green screen" remove shades that are not 100% green. That would seem to be the "pure" part. It also makes no sense to me why it's removing green from turquoise and not other colors.

I understand the value of removing shades close to green in real world situations, but I do not understand the value of not being able to remove only pure green.

 

[David Jimerson]

Well, that's not what "pure green screen" means. It means the baseline color it removes is pure 0 - 255 - 0 green and not a less pure shade of green, as most manual greenscreens are.

You can use the sliders to limit the range of tolerance; that might help.

 

[Justinec101]

I said in my first post that I played with the sliders.

It means the baseline color it removes is pure 0 - 255 - 0 green and not a less pure shade of green

That sounds like what I said. It's removing a less pure shade of green.

Turquoise Splotch - Red 28, Green 141, Blue 255
Yellow Splotch - Red 215, Green 215, Blue 0

Not only does the yellow splotch have more green in general, it has a higher percentage of green compared to the blue. And yet the yellow does not react in this way.

 

[David Jimerson]

No, it refers to the color it starts looking for, which is pure green. That doesn't mean it won't remove (or reduce) other shades, only that it starts at 255 green instead of elsewhere on the spectrum. Depending on how you have your thresholds set, it'll also affect colors which are near to it on the spectrum.

Turquoise is closer to pure green than either yellow or orange.

 

[Justinec101]

Ok that makes sense. I am thinking in terms of RGB, and it is doing it according to the color wheel. I still don't understand why no matter how far I move my thresholds, I can't get any of my turquoise back. It looks like the pure blue in my after pic no matter what I do.

 

[Lowlypawn]

I just spent about 20 minutes playing around with the picture you posted. No matter what settings I tired with the chroma keyer I got exactly the same results you did.

But I found 2 work arounds.

First one was to load the picture in Paint shop pro, apply flood fill to the green turning it black (I'm sure many other colors would also work). Then I loaded it back into Sony and the chroma keyer worked perfectly and didn't change the hues of the colors at all. So I guess the best solution is to use different screens.

The second workaround was to add a color curves, select the green channel, then grab the line about 2/3 from the left and drag is up midway. That gave me a color VERY close to the original and barely effected the other colors. But it did leave a slight outline so it's still not the perfect solution.

I guess this just proves green screen is not always the best solution. I suppose that's why blue screen (and other colors) are also used.