The term "polyphase scaling" is used at least by AMD: https://docs.amd.com/r/en-US/pg325-v-multi-scaler/Polyphase- https://docs.amd.com/r/en-US/pg325-v-multi-sc

The term "polyphase scaling" is used at least by AMD: https://docs.amd.com/r/en-US/pg325-v-multi-scaler/Polyphase- https://docs.amd.com/r/en-US/pg325-v-multi-scaler/Polyphase-... , that's why I used the term. This looks likes a custom video scaler and the context is custom filtering when one image is only slightly different in dimensions to another. How does that apply here? In isolation yes it doesn't make sense, but linear downsampling is a mere implementation detail here There is no such thing as "linear downsampling". There are box filters, triangle filters and other weighted averages, then there are more sophisticated weighting schemes that take into account more than just distance. that doesn't discard any pixel of the initial input. It creates more data then discards it by sampling too sparsely, but the sparse samples get linear interpolated so you don't notice the aliasing as much. This is not a technically sound way to upscale an image, it only can seem to work if you compare it to a poor enough example. If you want to see a better example look at bilateral upscaling, which would weight similiar pixels more heavily when doing interpolation, which should keep edges sharper. You can probably see this in motion with the right settings on a recent TV.