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rambomhtri
rambomhtri
Known Participant
July 28, 2020
Answered

How forgiving is the green screen for other different green shade?

  • July 28, 2020
  • 2 replies
  • 17495 views

Hi, I'm quite new to editing, I plan to do a green screen video with an object that is going to be all the time (would kill me to mask it manually, whatever this means) which color is far different from the "chroma key" green, but still green. It's a turquoise-mint-seafoam green, quite light/washed and noticeable different from the green screen's shade. The second problem is that the object is going to be directly surrounded by the green screen. I mean, it's not a green shade in the middle of another color object, it's an object which edge is going to be in contact with the green screen color.

Here are the colors:

 

Is it going to be a huge problem?

Or as long as the green is not very similar, you can work it out easily?

 

I chose green screen because I read it's the brightest for cameras, the most professional and it's easy to use due to tech specs of the color. The other option is buying a blue screen, but I just bought the green screen to do this project, and I've read that blue requires more advanced lightning as it's harder to work with.

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Correct answer Phillip Harvey

Blue screen would be ideal if your subject is going to be green. Honestly, any color would be good so long as it's not similar to the subject. Blue and Green are common because they aren't anything like skin tones/hair, etc., but in theory you can use any color as a key.

You can also use light and dark to help you key, usually called a luma matte. If your object was dark and you used a white background (or vice versa) you could create a matte to separate your object.

Can you use a green object with a green screen? Yes... But you better be very good at lighting your green screen. If your two green colors were as perfect as the colors you posted here then you'd likely be fine, the problem is that every tiny variation in green on your green screen is going to require you to expand the threshold to include more shades of green, and since your object is a shade of green not far off, you don't have a very big margin for error.

2 replies

rambomhtri
rambomhtriAuthor
Known Participant
July 28, 2020

I've done some testing and I can totally chroma key the seafoam object, but there's a huge problem: the object, although correctly keyed and defined, loses its color, it goes from seafoam/mint to a very light grey. In other words, it loses its color. What parameter should I adjust so the effect only makes transparent the selected green shade and doesn't change or removes any other shade of green?

Now that I think about it, many, if not all, colors in a video have some kind of green into them, only perfect reds or blues don't have any kind of green. So, there must be a way to work it out, because if not, green screening only would work with red or blues.

M
Michael Grenadier
Legend
July 28, 2020

you can actually create a hi-con that will "cut the hole" and then, theoretically, color correct your foreground image.  I used to know how to do this in fcp7 but haven't had to figure it out in Premiere but, often you think you've got a clean key but when you actually composite it, you see flaws...  That's why chroma-keying filters have all sorts of controls to clean up the edges, etc...and adjust the color of the foreground...

rambomhtri
rambomhtriAuthor
Known Participant
July 29, 2020

The range is part of spill supression, so it's adding some color correction in the opposite direction of the key color. If it were green, then it's going to add magenta to the image. If the key color is red, it's going to add blue, etc. It isn't actually effecting the key in any way, only color grading what is left over.

 

When doing your key, you can use the Alpha Channel output to see how precise your key is. Ideally your image is going to be black and white (just like a good luma matte). Anywhere that there are gray values in between black and white you are creating partial transparency. An example of a not-so-great background key here: 

In this picture the subject is keyed pretty well, but the green screen is not keyed so great. You could further refine this with the Matte Generation settings as best you could, but what is also usually done in combination with a key is to create a "garbage matte," which is a loose mask that animates around the subject so that you don't need to worry about a perfect key everywhere.. just on the subject. Like in the image above, if I started losing my good key on the subject so that I could better key the rest of the screen, that would be rather pointless.

Garbage Matte:

 

It's also worth noting that you have far more control over your keying in After Effects rather than Premiere.


Yes, I perfectly understand that picture and all you said, but here's the problem. Without changing the range, I can create a transparent background easily, but what happens is that what's left over suffers also a green removal: if it was yellow, it goes red, if it was cyan it goes blue, and if it had any shade or bit of green in the color mix, it disappears. If it's plain green BUT not exactly the green of the chroma, it goes grey.

 

Can't you reproduce that?

 

I mean, I understand what's going on, if I simply select the green of the chroma and apply, somehow Premiere Pro removes the green color as a whole, all of its shades, from the whole image, and then it makes transparent the green shade of the chroma. So, all colors are distorted, and I need to fix that. Not a single scene or image with a green screen will have absolutely no green in the objects or subjects, so my confusion is why tutorials that just go to the basic simply tell you to select the green of the chroma, may be touch a little bit the light, shadows... to make the edges smoother, but none of them mentions that you have to change the range.

 

I feel like I'm the only one experiencing these huge color distortions in the subjects.

P
Community Expert
Phillip HarveyCommunity ExpertCorrect answer
Community Expert
July 28, 2020

Blue screen would be ideal if your subject is going to be green. Honestly, any color would be good so long as it's not similar to the subject. Blue and Green are common because they aren't anything like skin tones/hair, etc., but in theory you can use any color as a key.

You can also use light and dark to help you key, usually called a luma matte. If your object was dark and you used a white background (or vice versa) you could create a matte to separate your object.

Can you use a green object with a green screen? Yes... But you better be very good at lighting your green screen. If your two green colors were as perfect as the colors you posted here then you'd likely be fine, the problem is that every tiny variation in green on your green screen is going to require you to expand the threshold to include more shades of green, and since your object is a shade of green not far off, you don't have a very big margin for error.

M
Michael Grenadier
Legend
July 28, 2020

shoot some tests... and even then you may be in for a bellyfull of pain.   My understanding is that the color space of the format you're shooting in can be critical...  Which means the camera you're shooting with is critical.  Do not expect great results if you're shooting h264...  Many cameras allow you to send the video to an external recorder with a much better color space...  but to a great degree, it's about your budget.  and having a dp who know's how to light for color key..., and making sure you have the time to have to light properly...  I was asked by a student of mine many years ago (when I was teaching avid editing)   about shooting a green screen program.  We'e talking maybe 25 years ago...  (I'm old, what can I say). I told her that the best thing was to have an ultimatte and switcher in the studio to be able to actually test the key before you shoot.  They chose NOT to spend the money and they landed up calling me in to handle the postproduction and. spending much more in post cause they cheaped out in production...  The software has gotten much more sophisticated since then, but still it's not simple...

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