How to Remove Noise when Animating background-size

Question

I have a div with a background image and I'm trying to change its scale infinitely.

I changed the background-size property in the animation but as you can see, there is some noise or vibration when animating. How would I remove it?

.pre-loader {
  position: fixed;
  left: 0px;
  top: 0px;
  width: 100%;
  height: 100%;
  z-index: 9999;
  background: url('https://upload.wikimedia.org/wikipedia/commons/a/ab/Android_O_Preview_Logo.png') center no-repeat #fff;
  background-size: 50%;
  animation: loading 5s ease-in-out infinite;
}

@keyframes loading {
  0% {
    background-size: 50%
  }
  50% {
    background-size: 55%
  }
  100% {
    background-size: 50%
  }
}

<div class="pre-loader"></div>

Answer 1

Consider a scale transformation to have a better rendring:

.pre-loader {
  position: fixed;
  left: 0px;
  top: 0px;
  width: 100%;
  height: 100%;
  z-index: 9999;
  overflow:hidden;
}
.pre-loader:before {
  content:"";
  position:absolute;
  top:0;
  left:0;
  right:0;
  bottom:0;
  background: url('https://upload.wikimedia.org/wikipedia/commons/a/ab/Android_O_Preview_Logo.png') center/50% auto no-repeat #fff;
  animation: loading 5s ease-in-out infinite;
}

@keyframes loading {
  50% {
    transform:scale(1.1);
  }
}

<div class="pre-loader"></div>

You are centering the background which means applying a background-position equal to 50%. The calculation of this value is related to the background-size so the position is changing slightly when the size is changing creating this bad effect:

If you consider a position using pixel values you will not see this effect:

.pre-loader {
  position: fixed;
  left: 0px;
  top: 0px;
  width: 100%;
  height: 100%;
  z-index: 9999;
  overflow:hidden;
}
.pre-loader:before {
  content:"";
  position:absolute;
  top:0;
  left:0;
  right:0;
  bottom:0;
  background: url('https://upload.wikimedia.org/wikipedia/commons/a/ab/Android_O_Preview_Logo.png') 50px 50px/50% auto no-repeat #fff;
  animation: loading 5s ease-in-out infinite;
}

@keyframes loading {
  50% {
    background-size:55%;
  }
}

<div class="pre-loader"></div>