opacity on off expression

[gdg59535]

sorry, i am a beginner  ...

i wanted to know if  i can make the opacity of a layer going on and off  (say 10 frames on and 10 frames off) with an expression  ?

[Mylenium]

Sure. Could be as simple as

Math.floor(time%10)*100;

which creates an alternating on/off animation every ten frames when applied to the opacity.

Mylenium

[Dan Ebberts]

This should work:

Math.floor(timeToFrames(time)/10)%2 ? 0 : 100

[Mmuza]

Is there a way to randomize this across a long timeline instead of constant pulsing?

[Dan Ebberts]

Probably. Depends on what you mean though. What are you randomizing? What are the constraints?

[Mmuza]

I have a collection of the same logo repeated across the screen and the client wants the opacity to slowly pulse but wants it to occur randomly. I can get the pulse to work properly but I don't have a way to randomize the timing of when they fade and reappear.

[Dan Ebberts]

That's still pretty vague. This might be one way:

// min/max on & off times in frames
minOn = 5;
maxOn = 40;
minOff = 5;
maxOff = 40;

t = tPrev = 0;
seg = 1;
while (t <= time){
  seedRandom(seg,true);
  myOn = framesToTime(random(minOn,maxOn));
  myOff = framesToTime(random(minOff,maxOff));
  tPrev = t;
  t += myOn + myOff;
}
time - tPrev < myOn ? 100 : 0

[Mmuza]

Thank you, Dan. This is almost exactly what I was looking for. Is there a way to smooth the transition by the amount of frames? Similar to the fade duration included in this expression.

fadeDuration = thisComp.frameDuration*48;
maxDelay = .5;
seedRandom(index,true);
delay = random(maxDelay);
t = time -(inPoint + delay);
linear(t,0,fadeDuration,0,100)

[Dan Ebberts]

Something like this maybe:

// min/max on & off times in frames
minOn = 10;
maxOn = 40;
minOff = 10;
maxOff = 40;

fadeFrames = 5; // should be less than minOn and minOff

t = tPrev = 0;
seg = 1;
while (t <= time){
  seedRandom(seg,true);
  myOn = framesToTime(random(minOn,maxOn));
  myOff = framesToTime(random(minOff,maxOff));
  tPrev = t;
  t += myOn + myOff;
}
t2 = time - tPrev;
f = framesToTime(fadeFrames);
t2 < myOn ? linear(t2,0,f,0,100) : linear(t2,myOn,myOn+f,100,0)