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Channel Boolean Basics


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#1 alexudell

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Posted 11 September 2013 - 09:31 PM

hi all

if I have an image with an alpha channel

and I create a color background of same dimensions of solid blue...

using channel booleans I should be able to create a blue shape cut with my alpha channel, right?

I'm trying this using copy...

using the RGB from one image and Alpha from the Alpha Channel of the other and copy mode.

but I end up with something I don't expect....

And I just want to understand why....Channel booleans is a key to the fusion kingdom....and I want to understand what I am missing....

see image for example....note the blue tinting in the wholly transparent alpha potions of the image....

this makes me feel pretty dumb....and it's frustrating as heck...

clarification would be very helpful...


thanks...

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#2 Tilt

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Posted 12 September 2013 - 12:59 AM

You would need to have the blue image as your BG, your car as your FG and then multiply all 4 channels by Alpha FG. Or if you want to keep your ChannelBoolean the way it is, set the merge to be substractive.

To be honest though, channel boolean is the wrong tool for this. The easiest way would be to connect the car to the blue background's mask input (optionally using a bitmap mask in between). The second easiest way is a MatteControl, with the car connected to the foreground and "combine alpha" selected and postmultiplication (which is enabled by default). Or you can use Gringo's Fill macro on your car.

#3 ChadCapeland

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Posted 12 September 2013 - 08:16 AM

I made a fuse to do exactly this. http://research.anat...1/05/set-color/

It's very useful for motion graphics and UI elements. Also good for mattes or making displacement maps. Probably my most used fuse.

As to the blue checker, Fusion currently ships with an AMl tool, so you don't need my earlier AlphaDivideMultiply fuse, but you might find my viewshader http://research.anat...ply-viewshader/ useful. It lets you stay in "straight" color which is great for uint8 compositing, but you will still see your premultiplied colors in the viewer (and that makes the checkerboard underlay better).




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