I'm reading a paper on how construct isotropic laplacian filter, and perhaps because it's an old paper, the notation in it really bothers me a lot. So can someone please explain it to me? For example, the notations I have highlighted in redline in the screenshot, such as what G and U mean and how to interpret these equations. I have no idea what these equation really means and how I should go about understanding it. enter image description here

  • $\begingroup$ This appears to be a two-dimensional convolution with 3×3 matrix. Is that correct? What is this 2-D filtering supposed to accomplish? Interpolation? Something else? $\endgroup$ Aug 11, 2023 at 2:10
  • $\begingroup$ @robertbristow-johnson Yeah. This is used to build an 9 point stencil (isotropic)laplacian filter. $\endgroup$
    – Ili a
    Aug 13, 2023 at 21:34


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