Compositing Over Operation in VOP

[kiko]

Hello everyone. I'm truing to replicate composting operation Over which I believe A+B(1-a). Instead I and up multiplying each layer by opposite alpha. It is work fine with constant colors, but it doesn't work with a texture. It turn texture (A) in opposite color. What wrong with that and what I missed?

 

composite_test_01.hip

[magneto]

Privet,

 

It has to be 1-$a, not $a-1, that's why it looks like that So:

$out = $A*(1-$a) + $B*($a);

[anim]

don't forget there is Composite VOP node which does that for you

[kiko]

anim, Composting node give unpredictable result for me. I cannot understand what it actually doing. 

 

magneto, I tried your suggestion but it didn't solve the problem. The texture A in this example is grey-scale and B constant red.

 

 

 

Edit: Composite node basically create the same result.

Edited April 3, 2014 by kiko

[anim]

first of all make sure your a is 0-1 so clamp it before plugging in as noise can easily produce values outside of that range

then magneto's advise should work

 

or easier, for your case you can just use Mix VOP as you are literally mixing 2 colors with a mask (still clamp it though)

 

Composite VOP expects premultiplied color, so if you multiply your red color with clamped noise and plug into A then clamped noise into Aa and your texture into B it will work

 

but just use Mix VOP for this

Edited April 3, 2014 by anim

[kiko]

Haha! Than you anim! It was a clam issue. Now I get this 3 nodes to work as I expected. Mix VOP is exactly what I need. 

I thought that aptitude 1 means that turbulent noise produce value from 0 to 1.

composite_test_01.hipnc