Problem with Primatte Clean FG Noise tutorial

[mostlyhuman]

I am currently doing the "Dynamically generating garbage masks using Primatte" tutorial in "Keying Greenscreens in Nuke 6.1". I do the step for Clean BG Noise, I draw an area with CTL_Shift and it works as expected (first pic), then it has me switch to Clean FG Noise and says to draw areas on the foreground and as soon as I draw my first box area the alpha of both the background and foreground clears back to mostly white (second pic)- any idea what im doing wrong?

http://www.all-in-order.org/primatteProb.jpg

Thanks in advance for any help!

[chrisg]

Hi mostlyhuman,

Judging from your picture on the bottom, you're selecting some of the greenscreen in that multi-selection. Make sure that you only select inside the foreground. Multi-selection works a bit different with Primatte. Instead of averaging every pixel in that box, it samples every pixel, so we need to be very careful not to select any greenscreen.

6131

Let me know if this clears it up or if you have more questions!

Hope you're enjoying the course.