Problem with Primatte Clean FG Noise

[mostlyhuman]

I am doing a tutorial to learn Nuke and its having me use Primatte and the first step is to use Clean BG, I draw an area with CTL_Shift and it works as expected (first pic), then it has me switch to Clean FG and says to draw areas on the FG and as soon as I draw my first box area the alpha clears back to mostly white (second pic)- any idea what im doing wrong?

Thanks in advance for any help! 😉

[Makayla Sherwood]

Someone else can probably give a way more technical explanation than this but without knowing your footage I’m assuming it’s because there are similiar color values on your FG and when you are sampling the areas you want to keep- Primatte thinks that you are going to also want to keep those same values that are part of the green screen. You might have some green spill on the FG or shes wearing something with the same color.

Judging by the hardness of the key in her hair I’d say your hitting your key quite hard which can be good for a core matte but sometimes this can mean your hard key with Primatte will struggle on those pixels, so you’ll need a second softer key to fill in that area, or a second core matte with a keyer that works differently to Primatte. Keying’s never a one hit solution so don’t worry too much. 😀

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