Explicit backpressure
每轮遍历后，最大元素会"冒泡"到末尾
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While this is immediately effective, the random perturbations introduce a disturbing texture that can obfuscate details in the original image. To counter this, we can make some smart choices on where and by how much to perturb our input image in an attempt to add some structure to our dither and preserve some of the lost detail.
for each pixel in image