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Expression efficiency (sampleImage)
An RGB value from one layer needs to affect another layer’s Opacity and Scale. So there are two options – use the sampleImage function in both scale and opacity OR reference scale in opacity:
Scale
target = thisComp.layer(“Layer1”);
value = target.sampleImage([x,y],[5,5])[0]*100;Opacity
target = thisComp.layer(“Layer1”);
target.sampleImage([x,y],[5,5])[0]*50;—–OR——
Scale
target = thisComp.layer(“Layer1”);
value = target.sampleImage([x,y],[5,5])[0]*100;Opacity
transform.scale[0]*0.5Is on of these options more efficient/faster/will cause me less trouble?
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2 Replies
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I’m not sure about performance–I suspect that sampleImage() gets run twice per frame either way, but I’d say try it both ways and find out.
Style-wise, I like the second way because it lets you tweak the sampleImage() parameters in one place.
Dan
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I agree with Dan. I’d also add that if one is going to be faster it’d be the 2nd one, but if there is a speedup it may not be noticeable.
Reducing the sample size should add a little to any speed gains.
Also note that sampleImage() expressions disable ‘Render Multiple Frames Simultaneously.’ For this reason I almost always convert the expression to keyframes before I kick out my final render. This can be a pain if you need to adjust the expression later, so I only recommend it once you’re happy with the results. This command is run with the properties you want to bake selected and is located here:
Animation > Keyframe Assistant > Convert Expression to Keyframes
Darby Edelen
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