title: What are the downsides of convolution by FFT compared to realspace convolution?
body: <p>So I am aware that a convolution by FFT has a lower computational complexity than a convolution in real space. But what are the downsides of an FFT convolution? </p>
  
  <p>Does the kernel size always have to match the image size, or are there functions that take care of this, for example in pythons numpy and scipy packages? And what about anti-aliasing effects? </p>