Sony a77 appears to fake video specs!

Started Feb 26, 2013 | Discussions thread
TrojMacReady
Senior MemberPosts: 8,462
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Re: Still not line skipping
In reply to Alphoid, Feb 26, 2013

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).

Regarding specific documents:

  • Good software downsampling, as in the F65 will eliminate moire without the need for an OLPF. Bad downsampling will give moire. Both will have identical or near-identical sharpness.
  • The 5D explanation does not make sense for the a77. The a77 crops, so it is not tied to downsampling for misaligned resolutions.
  • The D800 explanation, again, leads to moire and not softness.

The original page has been updated with images with simulated binning and line skipping. In both cases, the output looks much better than the actual a77 output.

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.

The A77 crop is for IS purposes, just like with the A99 (which does allow to remove it when turning off IS). Not so much to change sampling resolution.

Debayering results in a loss of roughly 30% resolution per axis. Not so when you're downsampling from a much higher resolution as done in the F65, or with your still image from 24MP.

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