3 ms·

This is wrong. Interpolation below Nyquist (downsampling) results in a subset of the original Information (capital I information theory information).

• astrange 4y ago
  Images aren't bandlimited so the conditions don't apply for that. That's why a vector image rendered at 128x128 can look better/sharper than one rendered at 256x256 and scaled down.
  • willis936 4y ago
    They are band-limited. That's why you get aliasing when taking unfiltered photos above Nyquist without AA filters. In your example the lower res image would be using most of its bandwidth while the higher res image would be using almost none of its bandwidth. Images are 2D discrete signals. Everything you know about 1D DSP applies to them.
    • orlp 4y ago
      One interesting complication for a lot of photos is that the bandwidth of the green channel is twice as high as the red and blue channels due to the Bayer filter mosaic.
    • astrange 4y ago
      If some of the edges are infinitely sharp, and you know which ones they are by looking at them, as in my example, then it's using more than all its bandwidth at any resolution.
      • willis936 4y ago
        That's true in the 1D case as well. That requires upsampling with information generation before downsampling. Using priori to guess missing information is a task that will never be finished and is interesting. It isn't necessary for a satisfactory downsampling result.