Do alpha mattes only work with clean, hd footage?

[Letty2019]

Have huge problems making an alpha matte that works clean.

My footage is old school crapola,  Standard digital 24p footage.  720x480 

When I make an alpha matte, black and white, the black matte seems to cover the object, plus a lot of fluff around the image as well.

Shouldn't the black matte part just stick to the face?

Should I just use Luma Key?   

If I have to manually go in and clean up the entire clip, what's the point of using alpha matte, when luma key is easier with same results?

Frustrating.

I was hoping the alpha matte would outline just the face, and not pcs of the background under her chin, etc.

and to make adjustments to the matte, the matte is black, so you can't see what you are doing.  I have to pull in the outline and feather, then check it in the comp to see the changes.  Can't make changes while seeing it at the same time.  Is that normal?

Thanks for your advice,

Letty

[Mylenium]

I'm not clear what you are getting at. Judging from the second image, this is a nigh shot and thus very dark. Directly using it as a luma matte therefore would not yield good results eitehr way simply because the skin tones still translate to a very dark grey in the matte, not white. You will need to process a duplicate of the layer in the pre-comp to fix that, which kinda is the point: You do so when using the luma key effect by tweaking the levels, but you're not doing it here. So to recap: There's almost definitely nothing wrong with the function, it's your methodology.

Mylenium

[Letty2019]

Hi, thanks for your advice,

The first pic is the actor with the background removed using alpha matte.  It was a day shot.

The 2nd pic is the matte with the new night background, which shows all the flaws in my alpha matte 😞

It seems my alpha matte is holding onto some of the day background and it looks like an outline around the image.

I get better results using Luma Key, but I know alpha matte is the preferred way to do this?

What do you think?

[Letty2019]

I could use some Refine Hard Matte tool and bring in the edge and feather it.  I wanted to avoid all that and get a clean alpha matte.

[Letty2019]

Turns out Luma Key works fine enough to wipe out most of it, then I used the Refine Hard Matte to adjust and feather....  works well enough.  

It's a dark scene, so I can hide the small variables in the darkness.  Got lucky!

Thanks for your prior.

Actually, on the HD tv, the scene is brighter and still looks clean.  Now to add her top head and body 😉

[Rick Gerard]

Your alpha matte is not perfect. You have to use masks, more procedural mattes, and do a lot more work so that you have a perfectly clean alpha matte. This will require stacking up layers, pre-composing the stack, and using that pre-comp as a track matte for the original footage. I thought I explained that in your other thread about the same shot. 

You can either build a stack of clean alpha mattes or create a black and white matte that can be used as a Luma matte. In the other thread, I clearly showed how to mask around the clean parts of the shot so they could be combined into a single usable matte.

[Letty2019]

I'm stackin the layers like pancakes. 

Thanks Rick 🙂