Sony a77 appears to fake video specs!

Started Feb 26, 2013 | Discussions thread
OP Alphoid Veteran Member • Posts: 5,333
Re: Still not line skipping

TrojMacReady wrote:

Semantics or not, the point stands that sampling by ignoring surrounding pixels when replacing them, is far more detremantal to the quality of output including resolution. Aliasing and moire (false detail as such) shouldn't be confused with real resolution to begin with.

This is completely false and incorrect. Subsampling maintains all of the resolution possible in the original image up to the Nyquist frequency of the new image. It maintain as much detail as is possible to maintain at the new resolution. Algorithms can do worse for resolution than subsampling, but they cannot do better.

The problems with subsampling have to do with aliasing (and, in particular, aliasing of noise). In most domains, downsampling is done by first including some form of linear low-pass filter. This reduces high-frequency detail (including noise), so it cannot alias into the new image. This low-pass filter is rarely perfect, and so it often has the unfortunate side-effect of reducing resolution in the new image as well. This is what the AA filter in your camera does. Sensors without AA filters are closer to subsampling, and therefore maintain better resolution at the cost of aliasing.

In image processing, for performance reasons, instead of a linear filter, you often use some kind of non-linear hack (e.g. various spline fits), but for the purposes of this discussion, it is the moral equivalent.

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