A580 vs A55 resolution

[pakodominguez]

It does look as if the image file has a slightly different low-pass filter treatment, and that may be all. I get a feeling that the A55 has a lower strength AA filter to enhance its sharpness a touch and compensate for any effect of the trans-mirror.

David

What is the function of the low-pass filter and how this affect image quality overall? Is there a better solution?

[David Kilpatrick]

All Bayer sensors require a low-pass filter which slightly blurs the image just before it reaches the surface of the sensor, ensuring for example that no single point of light ever reaches just a single sensel. Instead each point in the subject is received by a small cluster of RGB sensels, called a 'convolution', centred round its focus. The deBayer process involved deconvolution, or taking a calculated proportion of the values of all pixels surrounding the location of the point and adjusting the colour and brightness values according to the calculation.

Bayer sensors without a low-pass filter would allow very high frequency information (fine detail) to hit individual R G or B sensels precisely and this creates moiré, colour artefacts and jagged aliasing. It is possible to apply a strong deconvolution radius in software, as with Hasselblad Phocus software, to imitate a low-pass filter for sensors without an AA (low-pass) glass fitted.

David

[pakodominguez]

so, what is "better"?
a dense low-pass filter that correct moire or a weak low-pass that get you sharper images? can't moire be software in-camera corrected?

[agorabasta]

The correct way is not always better. A badly aliased image may still look very attractive due to perceived 'sharpness' and a lot of false detail. That false detail sits close to the real edges thus 'enhancing' them, so as long as there is no strong periodicity to cause moire, it may really look pretty good - a good example is the Nex5/3.

But the correct way is to have the total analog resolution (lens+LPF+filters...) about twice lower than the digital resolution. So ideally, the digital resolution should beat the best lens by a factor of 2. But practically a 40Mp APS Bayer would be about enough for an A3-sized image. Better yet to have an 80Mp striped layout with 1x2 format non-square sensels in RGBG columns. An FF needs twice that number of sensels...