AA filters

[Lee Jay]

Trust me, everybody in this thread would prefer to NOT have moire and false color, they just dislike fuzzy images even more (not to mention moire is relatively rare in the average photo).

Speak for yourself. Cameras that lack AA filters produce artifacts and nastiness that I dislike far, far, far more than slightly (barely) softer shots, which I can sharpen up satisfactorily anyway.

You can't sharpen what is not there in the first place. Software sharpening only enhances edge detail. It doesn't create detail.

AA filters remove almost no detail. That's why they still allow a little moire - the corner frequency isn't set low enough to prevent it, and so it doesn't remove anything.

Proven wrong time and time again. Remember, the pro-AA crowd, you, are talking bout theory; I am talking about practice. In every instance i have seen where AA filters have been removed and then that camera is compared to another camera of the same model that still has the AA filter, the one without the AA filter is showing more resolution.

No, more contrast at the pixel level, not more resolution.

Odd, I could have sworn the pro-AA crowd has said before that AA filters do not affect contrast. Which is it?

It affects local contrast (it's a low-pass filter, so that's its job). It does not affect global contrast.

When I can see or read actual detail that where I couldn't before, then that's more resolution. Simply adding more contrast would not have achieved that on a camera with a AA filter.

You can't see or read more actual detail, unless the AA filter is crummy, or the processing is crummy.

I was also addressing your claim of sharpening in software, which you then ignored.

That's because sharpening in software works to restore that pixel-level contrast, without adding false detail.

Software sharpening adds no detail, period. That's my point. You suggested otherwise.

Aliasing doesn't add any detail either. You're just confusing false detail with real detail.

 

[gaussian blur]

I think this argument can go round and round, bc it's not really about AA filters and signal theory.

Of course it's about signal theory. That defines how digital cameras work.

It's about standards (as much of what is on DPR is about). Nobody is saying AA filters are not needed,

Some people do.

we are saying that the current resolution ceiling imposed by artificial LPF is too low, we would rather deal with occasional moire than deal with less resolution all the time.

It's not the AA filter that's limiting it. It's the sensor. All the AA filter does is band-limit what is beyond the ability of the sensor to properly resolve and would otherwise cause alias artifacts.

And yet in every example I've seen where AA filters are removed real resolution increases.

Nope. False detail is what increases. Real resolution does not, since the AA filter is limiting what can't be resolved.

The problem is that after sampling, you can't remove aliasing because it's indistinguishable from real data.

Things like moire typically only affect very small areas of images, whereas the resolution degradation caused by the AA filter, as they have been implemented, affects the entire image.

You are the type that likes blurrier images so long as moire in tiny areas of the image is reduced.

Another ad hominem of yours. Anyone who disagrees with your nonsense must only like blurry images.

Anyone who is getting blurry images is doing something wrong. It's that simple.

Most photographers are the opposite of that.

Then it's a good thing they're getting just that, amazingly sharp images, isn't it? And that's with using cameras with an AA filter. So much for your idea.

The solution is a higher resolution sensor, or oversampling. The tradeoff is that smaller pixels have more noise and there is a lot more data to move and write to a memory card. Those problems are solvable, and eventually will be.

From a practical viewpoint there are no problems since people are obviously enjoying their sharp, high resolution photos.

Almost always from cameras with AA filters.

My non-AA filter Sigmas excel at that.

You're non-AA filter Sigma excels at producing false details along with excessive sharpening and a contrast boost which fools its users into thinking it's higher resolution than it really is. The image might have some 'pop' but it's far from accurate. It also has a lot more noise, pervasive blotching and odd colour casts that are localized and can't easily be removed. That's part of many reasons why Sigma enjoys less than 1% market share and shrinking.

 

[gaussian blur]

Moire affecting most scenes is rare, and typically affects small areas.

Whether it's rare or not depends on what type of photography someone does. Some people might never see it and others will frequently see it, depending on many factors.

Rare for most people and most scenes.

You can't make any generalizations, especially without referring to a particular camera. Whether it's rare or not depends on many factors.

I can, and I have. One only has to look at the photos of cameras without blur filters.

That's an invalid comparison.

How so? Do you not view photos with your eyes?

It's not a controlled test and eyes can be very deceiving. People see what they want to see, not what's necessarily there.

An example of a proper test would be comparing photos in a double-blind test taken with a D800 and D800e of the same subject, same exposure, processing, etc., with the only difference being an AA filter or lack thereof. Only then can you attribute the differences to the filter and not something else, like a better lens or better technique.

Comparing different scenes from different cameras of different resolutions taken by different photographers is completely meaningless, especially when the viewer knows which photos are which. Add confirmation bias to your ever growing reading list.

AA filters bandlimit high frequencies that are beyond the limits of the sensor which can't be accurately resolved anyway (and this isn't only about cameras either). Not doing that will result in alias artifacts, or false details not originally in the subject. Moire patterns is just one example.

Read a book on signal theory sometime.

Look up the difference between theory and practice sometime. In every digital photographic case where the AA filters are ditched resolution of the entire image is noticeably increased.

No it isn't. What's increased are alias artifacts, or false detail that wasn't actually there.

What you're claiming is mathematically impossible and no amount of your arguing is going to change math & physics.

Right, so the manufacturers like Leica are simply fooling photographers and what photograPhers are seeing is a figment of their imagination.

Leica does not have the ability to change math and physics.

The fact is that by omitting an anti-alias filter, there will be more aliasing, which is why it's called an anti- alias filter. It's basic signal theory.

A theory that is obviously not working out in practice.

Nonsense. It without question works out in practice. The sampling theorem has not been disproven, and certainly not by you.

It's like arguing with those who believe the Earth is flat or the moon landing was a hoax. No amount of actual proof will change their mind.

As they are implemented, they serve no reasonable purpose. In practice with digital cameras they clearly reduce resolution. there's no getting that.

AA filters do not reduce resolution. They bandlimit what can't be resolved, which is a requirement for a properly implemented sampling system. Otherwise you get aliasing artifacts.

Since no perfect AA filter exists, there are tradeoffs to be made. It's just the way it is. We live in an imperfect world.

First you say "AA filters do not reduce resolution" and then you say "no perfect AA filter exists, there are tradeoffs to be made?"

If you understood signal theory, you'd not be asking that.

No, you just got caught contradicting yourself.

I didn't contradict myself.

If you think I did, then it's even more evidence you don't understand the topic.

 

[gaussian blur]

No, digital images are made up of pixels. Look close enough and you will always see stairs on the edges of diagnol elements. No getting around that.

There is when the sampling rate is high enough.