all-a-blur

It’s all a blur, Icamtuf

But then, it’s not wrong to scratch your head. Blurring amounts to averaging the underlying pixel values. If you average two numbers, there’s no way of knowing if you’ve started with 1 + 5 or 3 + 3. In both cases, the arithmetic mean is the same and the original information appears to be lost. So, is the advice wrong?

Well, yes and no! There are ways to achieve non-reversible blurring using deterministic algorithms. That said, in some cases, blur filters can preserve far more information than would appear to the naked eye — and do so in a pretty unexpected way.