[MEP17+] Gray key image matte...

Gorf wrote on 1/6/2013, 6:35 PM

...or at least that's what it was called in my old video editor.

I'm trying to use a monochrome bitmap image (actually a white-to-black gradient) to assert which pixels of my video clip are visible and which are (semi)transparent, showing the underlying video. 

I cannot figure out how to do it. Essentially I have 720p and 576p videos, and want the 576p clip positioned screen-right, scaled up, and with a nice fade along its left edge to mix gracefully with the underlying 720p video.

Comments

cpc000cpc wrote on 1/7/2013, 5:53 AM

Gorg,

I've not got MEP17 to check just how it does it (14Plus >> 2013Premium) but what you want is 'alpha' chroma key. Basics are a stack of three tracks:

  • Background image on higher (lower number) track.
  • Alpha mask -- governs what's seen eg where it's black you see up and where white you see down.
  • Foreground image on lower (higher number) track.

In MEP 14+ you would select your mask / matte and hit [Shift + Y] to bring up the real time video effects editor window and pick Alpha MIX FX. In more recent versions select your mask track and go to the 'Effects' tab >> 'Video effects' >> ' Chroma key' >> 'Alpha'.

There are sliders which you can adjust the cutoff values and your alpha track will get an up/down arrow icon at its start which you can click to reverse the effect eg black sees down, not up.

There has been some further discussion about alpha masks here http://www.magix.info/us/mental-model-for-working-with-alpha-masks.forum.885885.html

Regards,

Carl

Gorf wrote on 1/7/2013, 6:40 AM

Many thanks, Carl. My mistake was to add the gradient image using the dropdown box in the chroma key window itself. I'm sorted, now :)

cpc000cpc wrote on 1/7/2013, 7:30 AM

Glad to hear you're up and running. A tip mentioned elsewhere -- if you name your mask filename_alpha.jpg etc, it will load with the alpha effect automatically. You can still go to the window to make adjustments.