I have a wedding video to edit, and i really want to do this effect durring the reception. for the clips of them dancing, there are dozens of green balls hanging from the ceiling. What i want to do is have after effects select and keep the green and make that its own layer. then with the original layer underneath, make that desaturated, and the green ball layer have a glowing effect. I know i can do this with a bunch of masks, but i dont have the patience to mask them all with 2 mins worth of key-framing. so far i was able to select the green using hue/saturation, but it keeps it as one layer. any thoughts?
I would suggest that you try the Roto Brush. Create two copies of your video. On the front one, try the Roto Brush, which will create an automatic mask which will follow any movement pretty well - make sure you look over the Roto Brush tutorials first on the Adobe site, or elsewhere - it's not intuitive. Once you have the green balls roto'd, you can precomp them and add a glow.
There are numerous ways to accomplish this effect.
For a single layer with a single effect: add Hue/Saturation to the layer, then click on the drop-down menu for Channel Control. Individual select the Reds, then turn down the Red saturation. Move on to the Yellows. Repeat for Cyans, Blues, and Magentas. Finally, select the Greens and tweak the channel range as necessary to properly isolate the effect.
You can exert quite a bit of control over the tone of the desaturated image by adjusting the individual lightnesses of the reds, yellows, cyans, blues, and magentas. You'll probably want to leave the green saturation and lightness alone, to keep those tones from looking too artificial.
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