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Opacity on/off via alpha of certain layer
I have various shape layers whose opacity I want to turn off or on based on the alpha of a layer passing under it.
So I want to have the shape layer’s opacity turn on when another layer passes the center point of the shape.so I need a sample point expression for the shape layer to drive an if/else expression for the opacity of shape layer.
Thanks
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4 Replies
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I found this expression from dan
target = thisComp.layer(“background”);
target.sampleImage(transform.position, [width, height]/2, true, time)this works for animating the color of a fill effect turning it black when there is no layer under it but how do I get it into an opacity expression.
I think I need the sample to reduce down to a 1 element array for opacity.
Can anyone help me in this train of thought?Thank You
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I figured it out for myself and this is what I used
target = thisComp.layer(“Audio_PC”);
rgb = target.sampleImage(transform.position, [5, .5], true, time);
hsl = rgbToHsl(rgb);
if (hsl[2] > 0) 100 else 0I’m sure there is a way to skip the rgb to hsl conversion but I found that in another post and then just added the if else.
I’m happy
Now if some one could tell me how to ad a 10 frame fade out from 100% opacity (on) to off : )
Thank You
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Hi Riccardo,
using hsl doesn’t really make sense, because in your example you’re actually looking at the brightness of the pixel, not the alpha. They may be the same, but not necessarily when your layer has asoft edge for example
However, sampleimage actually returns a 4 number array: rgba,
so you can just use:rgb[3] to get the fourth value.
Also this expression didn’t take into account layerspace transform, so I’m not sure how it could work if the layers are not compsized and moving.
I came up with this:
fd=thisComp.frameDuration;
fade=10; //framestarget = thisComp.layer("Audio_PC");
alpha=0;
for (t=0;tIn the 'for'-loop it averages out the sampled alpha's in a 10 frame window, so you get a natural fade-out.
I put the last 2 lines in so, it would flash on immediately when it enters the alpha, but fade out when it leaves. If you want it to also fade in, the last 2 lines should simply be:alpha*100;
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After rereading your first post, I realised a difference in my solution: if the layer underneath has an alpha of 50%, the toplayer would also have an opacity of 50, this version should fix that:
fd=thisComp.frameDuration;
fade=10; //framestarget = thisComp.layer("Audio_PC");
alpha=0;
for (t=0;t < fade*fd; t+=fd) {
alpha += target.sampleImage(target.fromComp(toComp(anchorPoint,time-t),time-t), [1, 1], true, time-t)[3]>0 ? 1/fade : 0;
}
alpha_now=target.sampleImage(target.fromComp(toComp(anchorPoint)), [1, 1], true, time)[3]>0 ? 1 : 0;
Math.max(alpha,alpha_now)*100;
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