Ultra Key – green screen

[Chris Wright]

can you post a full frame png image?
does AE’s keylight work better in intermediate format?
what is your green iRE at?

if what you say is true, then basically taking a pure solid layer in premiere and appling ultra key creates noise, right?
why would it only dislike gh4?

how are you viewing, in full res? output format?

[Anthony Marotti]

Hello,

Thanks for the response, I didn’t think might see my post.

I haven’t tried AE yet, but may once I have the time to get in there and learn Keylight.

I shot the screen from 60IRE to over 90IRE and in every case there was noise introduced.

Let me clarify because I couldn’t edit my first post for some reason.

At 400% magnification you can see some very, very fine noise in the original clip. I don’t know if any sensor can produce an image with no noise.

But this very fine grain like noise becomes big blotchy serious noise (in comparison) once the key is applied.

You gave me a good idea that I’m going to try as soon as I get back to my workstation.

I’ll create a solid green HD size graphic, and I’ll create a solid square graphic that I can place in the center say 450X450 and apply UltraKey to that.

As you mentioned, if the process doesn’t produce noise, then we know more about the problem.

If it doesn’t create noise with completely noiseless elements, that doesn’t mean that UltraKey isn’t amplifying noise in my clips, but it is an interesting test.

As far as posting a full frame PNG… are you suggesting creating a snapshot of a frame in CS6?

I don’t have any other footage at the moment to test anything other than the GH4. Maybe I can find a clip from a camera that is known for getting good keys and key that in CS6… Do you know of any sources off hand?

Thank you so much for your interest, I’ve been out of the game for a while and am just now getting back in.

Anthony

AM 🙂

[Anthony Marotti]

Hello Again 🙂

OK the tests with solid objects on a solid object background proved your point that Ultra Key wasn’t creating the noise, at least under these conditions. No noise was visible when using and keying all solid graphics (non movie clips).

Again, as I mentioned before, I don’t know of any sensor that is noise free, and the next test I ran using the GH4 footage should prove my point that Ultra Key actually amplifies any grain or noise present in the video footage.

All of the footage is shot at 4K and 100Mbp and magnified so that any noise in the original footage could be seen.

I exposed the green screen correctly but purposely underexposed the face so that it would have more noise for this test.

With that said, if shown at normal magnification and at the proper viewing distance, the noise in the non-keyed footage would be undetectable, even in the shadows of the face.

The following clip shows the footage with and without the Ultra Key Filter applied.

The first series of shots focus on the eye of the model so that you can see the noise amplification effect without the distraction or implications of the keying issue.

The next shot series deals with fine hair against a green screen. Here I did not use an underlying graphic as it would distract from the test and I did not try and get a great key, because that also would obfuscate the test results.

What you will see is a clear amplification of noise any time the Ultra Key Filter is applied.

Let me know what you guys make of it.

Thanks!

Here is the clip:

https://youtu.be/6USbtSHfIpg

AM 🙂

[Duke Sweden]

Why is this thread first in line when the last response was 4 years ago? Oh well, being that I’m a green screen enthusiast I thought I’d add something. Now, I know my green screens are a challenge since I have so little room to work, but I’m currently doing another one of my short films, and I’m using some of those green screen clips on youtube. The background is perfectly smooth, bright green, yet I still have problems getting a good key. Way too much work considering how good the key is.

Could it be because of youtube’s compression?

[Chris Wright]

can you post a simple raw screenshot of the greenscreen with model? my opinion is that the key isn’t a perfect alpha and
the alpha matte is burning through randomly resulting in noise. so a screeny of the white/black alpha matte would also be a big indicator.

[Anthony Marotti]

Hi,

The reason I included the clips of the eyes only is to make the point that regardless of any key specific issues, like even or proper exposure of the green screen, key settings, etc. that isn’t relevant to the main problem… Adding the Ultra Key Filter amplifies and makes minor noise horrible.

Just look at the left eye. Without the key you can see minor noise that you might expect at 400% magnification and a underexposed subject.

As mentioned, at 100% magnification and at the proper viewing distance, you wouldn’t think there was any noise at all… it’s pretty clean.

But as soon as you add the Ultra Key, you can see noise everywhere and look closely at the left eye… with out the key there’s some fine grain but negligible, but with the Key on, you can see some pretty disruptive noise.

So it doesn’t have anything to do with the background at all, addint the Key magnifies the noise Everywhere, so that means it doesn’t have anything to do with the background only something peculiar within CS6 in communion with Ultra Key.

I’ll try some of the other keyers to see if they do the same thing… it might just be how CS6 handles keys??

I can’t be the only one that this is happening to.

I would like to see if anyone can replicate this.

Next Ill try resetting the key and not choosing a key color. I susspect it won’t make a difference.

I’ll also try a different keyer.

Thanks!

Anthony

AM 🙂