Is there any way to use a difference matte in FCPX? There's a similar feature built into ichat and photobooth video effects, anything close in FCPX?
Thanks
For a clip, you can choose its compositing blend mode. "Difference" is one of the choices. You can also control the opacity for the composite. To access this, use the inspector when selecting the clip. Compositing is at the bottom.
Close, but not quite (and my terminology may be off). The composite with difference blend looks like it's subtracting color values. So the resulting image looks like a negative. What I'd really like to do probably needs a green screen used with chroma keying, but what I was hoping for was a similar effect without the screen. Similar to what's done in the ichat and photobooth video effects... you record your current background (whatever it is) for a few seconds and when you step back into frame a new picture can be placed behind you. The effect that's built into ichat is pretty crude, but I was looking for something similar here.
Ah, yes, you are talking about chroma keying. Depending on the complexity of what you are trying to accomplish, you might be able to make do with the built-in FCPX chroma key and matte effects. Otherwise you may need to use Motion which has more extensive keying and masking capabilities.
derrin wrote:
you record your current background (whatever it is) for a few seconds and when you step back into frame a new picture can be placed behind you.
That sounds like a difference matte. In effect, the application grabs a still of the background without you, then when you move in front of it, any pixels that are different from the background result in white pixels in the alpha channel.
Just guessing here, but you could take the still of the background, do a difference composite mode with the foreground video to extract the different pixels, convert that to black&white, use a threshhold to make all the grey areas white, then use one of your rgb channels as a matte to composite your foreground video against the new background. I'm sure hafken could help with the details.
You would get more consistent results with a green screen, however. The problem with difference mattes is that if there is any camera noise, that results in different pixels, and therefore messes with your matte. Also, if anything you're wearing happens to match what's behind you, you'll get a transparent pixel. So, while you could mimic the iChat effect to some degree, you should really use either a green screen and chroma key or a white screen and luma key.
Agreed, and confirmed. I managed to replicate the Photo Booth effect, but the result is questionable, I guess that's the reason it's not included in FCPX. It's not PRO, in the approach already. However, if you wants to try, here are the steps:
1. Put the clip on to of the background still in timeline.
2. Set the clip's Composition mode to Difference. Now you have a (probably noisy) black background with a weird colored foreground shape.
3. Create a compound clip with the still and the clip.
4. Put a new copy of the original clip underneath the new compound clip.
5. Use Luma keying effect on the compound clip to have a black background with the correct colored foreground shape.
6. Make another compound clip with these 2 clips.
7. Put your desired background underneath this second new componund clip.
8. Use Luma keying effect on it to have the final desired result.
Difference Matte in FCPX?
