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:

Alphoid wrote:

An optical low-pass filter is the way to battle aliasing. The a77 does not have an OLPF (or it does not have one that would have any effect on a 2MP video; the AA filter is designed for a 24MP image).

A software low-pass filter would not solve moire. A low-pass filter, to reduce moire, has to come before the aliasing. After the aliasing comes into play, high frequency are already translated into low frequencies, and a low-pass filter will not effect low frequencies.

There are many ways of sampling (software) that can influence aliasing. That's one of the reasons why so many sampling algorithms yield different results regarding aliasing (and moire).

Correct. This contradicts nothing I said.

The Sony documentations shows there is a difference in sharpness too. And again, we're not talking about downsampling vs downsampling in your example, but downsampling vs subsampling. The latter comparison can definitely give subsantial differences.

Your definition is incorrect.

Subsampling is one form of downsampling. In most applications, downsampling is implemented as a lowpass filter followed by subsampling. Subsampling is the special case where that lowpass filter is 1. Subsampling loses no resolution -- it just results in very bad aliasing. The page includes an example image where downsampling is implemented as subsampling (as a link in the bullet list at the bottom). You can compare. The image looks very good compared to the video which comes out of the a77.

(Footnote: The definition I give is not universal. In some fields, subsampling and downsampling mean the same thing. There is, however, no definition I am aware of which makes your statement correct.)

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