Sharpness/detail and anti-aliasing filter - why not get rid of all AA filters?

[Armanius]

It goes without saying that there is direct correlation between sharpness/detail and anti-aliasing filter. The Leica M8/9 apparently do not have AA filters, and therefore, are capable of rendering lots of detail. The recent Oly Pens are said to have weaker AA filters. My experience with the older Pens like the EP2 and the Sony NEX3 is that their images do appear to be softer than the M8/9 and my Panasonic GH2. My basic understanding of AA filters is that they prevent moire. But in looking at the images taken with my M9, I often never noticed any moire. Or at least nothing significant that jumped out at me and made me wish the M9 had a AA filter.

All of this being said, why are camera manufacturers still using AA filters?? If I'm a camera manufacturer, I want my camera to be able to capture maximum detail. So why not just get rid of it altogether?

 

[Armanius]

I guess AA filters is a boring topic!

 

[Djarum]

Armanius,

Antialiasing is somewhat complex, so I'll try to give you the simple version.

Basically, a sensor is trying to record an image with both low and high frequency spatial information. What I mean by high frequency is that the information has really fine detail, for example. If the sensor is recording part of an image that has higher detail than the sensor can really resolve, nasty things start to creap into that part of the image. That part of the image is undersampled. An AA filter is a low-pass filter for resolution. The stronger the AA filter, finer detail gets smoothly blurred out at the cost of losing maxiumum resolution. On the other hand, the weaker the AA filter, the greater the resolution, but the higher chance that artifacts such as Moire will creep in.

For example, weak AA filter:

Olympus E-PL1 Review: 7. Resolution Test: Digital Photography Review

Stronger AA filter:

Olympus E-P1 Review: 17. Photographic tests (RAW): Digital Photography Review

As you can see, the E-PL1 starts to show moire artifacts at around 2400 lph, but it has overall greater absolute resolution vs the E-P1. Looking at the E-P1, which has less overall absolute resolution, doesn't have the nasty moire as resolution increases. Instead, the lines smoothly blurr together.

 

[Travisennis]

Djarum, thanks for that explanation. I think it was the first time I really understand the advantages and tradeoffs of an anti-aliasing filter.

 

[Promit]

There are cameras that exclude the AA filter entirely. Leica X1 comes to mind.

 

[RT_Panther]

Then there's the film option....

 

[Armanius]

There are cameras that exclude the AA filter entirely. Leica X1 comes to mind.

I guess that's my point. It sure seems like most users tend to rave about the details a sensor is capable of on cameras that have weak (or no) AA filter. It sure seems logical then that manufacturers would lean towards that direction. In had a M8 briefly, and that camera yielded some of the sharpest photos I've seen, more so than the M9.

Thanks for the great explanation DJ!

 

[Amin Sabet]

Oversampling prevents aliasing, so the cameras with the highest pixel densities have less need of AA filters. I think that 24MP for APS-C and 16MP for Micro 4/3 are in the range where I'd rather get rid of the AA filter and deal with aliasing when it pops up, but this is a matter of personal preference.

 

[Djarum]

I guess that's my point. It sure seems like most users tend to rave about the details a sensor is capable of on cameras that have weak (or no) AA filter. It sure seems logical then that manufacturers would lean towards that direction. In had a M8 briefly, and that camera yielded some of the sharpest photos I've seen, more so than the M9.

Thanks for the great explanation DJ!

I haven't seen images from that camera specifically, but I wouldn't take pictures of anyone wearing certain ties or shirts that would give a moire effect. It's all about balance. I think the E-PL1, for example, gives a good balance.

 

[Djarum]

Oversampling prevents aliasing, so the cameras with the highest pixel densities have less need of AA filters. I think that 24MP for APS-C and 16MP for Micro 4/3 are in the range where I'd rather get rid of the AA filter and deal with aliasing when it pops up, but this is a matter of personal preference.

Well, then we can get into under sampling because of the lenses. But yes, if the lens is up to it, removing the AA on higher megapixel cameras would be the way to go.