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Author Topic: Is it past time to say goodbye to the AA filter?  (Read 14279 times)

David Watson

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Is it past time to say goodbye to the AA filter?
« on: September 14, 2011, 03:04:30 pm »

I really think so.

I recently decided to downsize from medium format digital back to 35mm.  I am getting older and I simply couldn't easily carry my MFD kit around any more. (for those interested I was using a Hasselblad H4D-50 and half a dozen lenses, filters, batteries etc but it could easily have been another system).  I decided to buy a Nikon D3X with a few lenses as my "serious" outfit and a Leica M9 for walkabout and holidays.  The Nikon is a nice camera, no question, but I just couldn't get to like the images.  After the Hasselblad they seemed somehow soft and lacking punch, bite whatever.  The M9 on the other hand was like a mini-Hasselblad, sharp as a tack and a joy to use.

Last year I used a Sony A900 for a month and liked the combination of the sensor and the Zeiss lenses so I sold the Nikon and bought a Sony outfit (not too bad on Ebay).  Again I found myself comparing the output from the Sony unfavourably against the M9 and indeed the Hasselblad.  It is now up for sale.

My position seems to be that once I had moved from 35mm digital (Canon and Nikon) to MFD I not only gained some megapixels (no big deal) but more importantly lost that damn AA filter and I can't go back.

If Leica can make a camera without an AA filter in 35mm format why cannot Nikon/Sony/Canon?  It seems to be that it is now redundant for cameras with 18-25 megapixel sensors.  Am I wrong, am I missing something, or what?

What do you all think?
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hjulenissen

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Re: Is it past time to say goodbye to the AA filter?
« Reply #1 on: September 14, 2011, 04:03:42 pm »

I believe that the company below will remove the AA-filter of certain cameras for a price:
http://www.maxmax.com/hot_rod_visible.htm
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Bart_van_der_Wolf

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Re: Is it past time to say goodbye to the AA filter?
« Reply #2 on: September 14, 2011, 07:14:09 pm »

What do you all think?

Hi David,

I'm not all, but I think you should have a look at deconvolution sharpening before wanting to throw out the benefits of AA-filters. Why do you think the manufacturers add a sandwich such an expensive piece of material? The reason that MF camera manufacturers leave them out is not because it increases quality (ask anybody with even half a brain in DSP), but because it would be prohibitively costly, and DOF is limited so diffraction generated by having to close down the aperture can function as a surrogate Low-pass filter. In MF the magnification factor on sensor is also larger than on (cropped) 35mm sensors, thus lowering the artifact risk a bit.

Having said that, I wish it would be possible to get rid of an optical low-pass filter (OLPF) without also increasing risk of aliasing artifacts hurting the images, especially because Bayer CFA sensors will create false color aliasing which is often only too easy to detect (depending on subject matter) but may be difficult to hide in postprocessing. Besides, wasting time in postprocessing when it can be dealt with when shooting seems unproductive to me.

Cheers,
Bart
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gss

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Re: Is it past time to say goodbye to the AA filter?
« Reply #3 on: September 14, 2011, 07:54:49 pm »

I'm not all, but I think you should have a look at deconvolution sharpening before wanting to throw out the benefits of AA-filters.
Bart,
The manufacturers know the nature of the AA filters that they use, so it strikes me that they would know the best way to deconvolve the filter.  Why is it that they don't have this sharpening automatically done in their raw conversion software?

From personal experience, I hate that the Nikon D3X always seems to overdo the AA.  I have tried a few sharpeners with deconvolution (some type of Richardson-Lucy), but some are no longer supported on current operating systems, and none have really done the trick.  I much prefer the files I get from MFDB.
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ErikKaffehr

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Re: Is it past time to say goodbye to the AA filter?
« Reply #4 on: September 15, 2011, 12:09:02 am »

Hi,

It's not clear what is depending on lens, pixel size and AA filtering. One thing that is pretty clear is that AA-filtered images require much more capture sharpening than images without AA-filters, normally small radius and high amount. I normally use Lightroom and use radius < 1, amount around 40 and detail slider fully to right. That's pretty much OK on the Alpha 900 but excessive on the Alpha SLT55 which seems to have a weaker AA-filtering.

Another issue is lenses. Leica lenses are renown for uncompromising quality comparing a Sony ZA zoom with a Leica prime having twice the price may put the Sony at disadvantage. The Leica has also larger pixels, so if we would compare the image at actual pixels the Leica would have a significant advantage in MTF, like 15% higher MTF. That advantage would go away if the images were scaled to match.

One issue with aliasing is that it results in fake detail. With the Bayer matrix, normally used on DSLRs it causes obvious colorful Moiré patterns, but the fake details may also be perceived as better contrast.

A very good example of fake resolution is here: , note that at around 18 the lines disappear but at 22 they are back, but being fewer. This is typical of images without OLP filtering where the lens has significant MTF at the Nyquist limit. The image links to the DPReview test of the Sigma DP2, a camera with Foevon sensor and not having OLP filter.

I made a comparison of sample images from the Leica S2 and the Nikon D3X by Lloyd Chambers. Lloyd is painstaking in his testing, so the images were probably as close as possible in field shoots. My findings are here: http://echophoto.dnsalias.net/ekr/index.php/photoarticles/38-observations-on-leica-s2-raw-images .

So, I would say the issue is complex. OLP filtering is technically necessary but removing it leaves more MTF at fine detail in the image. That MTF will normally results in artificial detail, which may seem to enhance the image. OLP filtering needs some aggressive extra sharpening. Sharpening would also enhance noise, so we may need extra noise reduction. Stopping down f/11 may reduce AA-effects significantly.

I have also seen really bad Moiré in a Pentax 645D sample shot . That article is here: http://echophoto.dnsalias.net/ekr/index.php/photoarticles/51-a-closer-look-at-pentax-645d-image-quality

Moiré or not I would be interested of the Pentax 645D, except that I don't really have the money to burn, but also for weight reasons. I'd need a lot of lenses to replace my 135 equipment. Flying with a significant photographic equipment is a real challenge.



Best regards
Erik

I really think so.

I recently decided to downsize from medium format digital back to 35mm.  I am getting older and I simply couldn't easily carry my MFD kit around any more. (for those interested I was using a Hasselblad H4D-50 and half a dozen lenses, filters, batteries etc but it could easily have been another system).  I decided to buy a Nikon D3X with a few lenses as my "serious" outfit and a Leica M9 for walkabout and holidays.  The Nikon is a nice camera, no question, but I just couldn't get to like the images.  After the Hasselblad they seemed somehow soft and lacking punch, bite whatever.  The M9 on the other hand was like a mini-Hasselblad, sharp as a tack and a joy to use.

Last year I used a Sony A900 for a month and liked the combination of the sensor and the Zeiss lenses so I sold the Nikon and bought a Sony outfit (not too bad on Ebay).  Again I found myself comparing the output from the Sony unfavourably against the M9 and indeed the Hasselblad.  It is now up for sale.

My position seems to be that once I had moved from 35mm digital (Canon and Nikon) to MFD I not only gained some megapixels (no big deal) but more importantly lost that damn AA filter and I can't go back.

If Leica can make a camera without an AA filter in 35mm format why cannot Nikon/Sony/Canon?  It seems to be that it is now redundant for cameras with 18-25 megapixel sensors.  Am I wrong, am I missing something, or what?

What do you all think?
« Last Edit: September 15, 2011, 01:05:38 am by ErikKaffehr »
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ErikKaffehr

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Re: Is it past time to say goodbye to the AA filter?
« Reply #5 on: September 15, 2011, 01:01:12 am »

Hi,

Here is a comparison of Pentax 645D and Nikom D3X images. The images were scanned from A2-size prints, so they went trough the full image processing pipeline:

Left Nikon D3X, "landscape sharpening", center Nikon D3X deconvolution sharpening, right Pentax 645D "landscape sharpening".

Landscape sharpening is probably:

Amount 40, radius 0.8 detail 35 masking 0

Deconvolution sharpening was probably:
Amount 45, radius 1.0, amount 100, masking 17



Full size image: http://echophoto.dnsalias.net/ekr/images/Pentax645D/A2_print_center.jpg

From the same image A0-size prints were also tested:


Full size image: http://echophoto.dnsalias.net/ekr/images/Pentax645D/A2_print_finetext.jpg
Note: the images were not actually printed in A2 or A0 but corresponding crops were made that were printed in A4 size.

« Last Edit: September 15, 2011, 01:03:14 am by ErikKaffehr »
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BernardLanguillier

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Re: Is it past time to say goodbye to the AA filter?
« Reply #6 on: September 15, 2011, 07:26:08 pm »

It is interesting how we always end up trusting our eyes better than science.  ;D

From a signal processing standpoint, it sounds clear that the lack of AA filter results in images that are intrinsically flawed in that they create information that was simply not there in the initial scene. That is regardless of the fact that these information "seem" real.

The example of the resolution chart of Erick is totally clear on this one. These images are full of fake details that seem sharp but simply are not true.

Yet, most perfectly reasonable owners of non AA filter backs will swear that their imaging device delivers images that are more true to the scene than AA filtered images. :)

I am pretty sure though that companies like Canon and Nikon who has striven very hard until now to release cameras delivering AA filtered images as truthful as possible to the actual scene will in the end give up and follow the hype with AA filterless devices.

Is the truthness of our images really important? Probably not in the end.

Cheers,
Bernard

feppe

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Re: Is it past time to say goodbye to the AA filter?
« Reply #7 on: September 15, 2011, 08:33:50 pm »

I am pretty sure though that companies like Canon and Nikon who has striven very hard until now to release cameras delivering AA filtered images as truthful as possible to the actual scene will in the end give up and follow the hype with AA filterless devices.

Is the truthness of our images really important? Probably not in the end.

I bet Canon and Nikon and others are more worried about the unwashed masses seeing ugly moire on the bride's dress than squeezing marginal amounts of sharpness. Sharpening is one slider for most people, but fixing moire in post requires more effort.

I understand moire becomes less of an issue the more resolution there is, though. Does that hold even for down-rezzed pics? As more and more photography never leaves the computer screen, moire might be an issue for years.

BernardLanguillier

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Re: Is it past time to say goodbye to the AA filter?
« Reply #8 on: September 15, 2011, 10:25:43 pm »

I bet Canon and Nikon and others are more worried about the unwashed masses seeing ugly moire on the bride's dress than squeezing marginal amounts of sharpness. Sharpening is one slider for most people, but fixing moire in post requires more effort.

I understand moire becomes less of an issue the more resolution there is, though. Does that hold even for down-rezzed pics? As more and more photography never leaves the computer screen, moire might be an issue for years.

Sure, moire is the most obvious example of what I wrote above.

I consider it as a prime example of false detail, in this case in the color domain.

Cheers,
Bernard

ErikKaffehr

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Re: Is it past time to say goodbye to the AA filter?
« Reply #9 on: September 15, 2011, 10:42:04 pm »

Hi,

Aliasing also occurs when down-rezzing an image. The correct way to down-rezz is the to blur the image slightly before resolution change and sharpen slightly after rescaling. On the other hand the image is already demosaiced, and we don't have an underlying Bayer pattern any longer, so something we will not see is color moiré.

http://bvdwolf.home.xs4all.nl/main/foto/down_sample/example1.htm

or based on test chart:

http://bvdwolf.home.xs4all.nl/main/foto/down_sample/down_sample.htm

On the other hand, according to Eric Chan, Adobe tested something like 30 different scaling methods to use in Lightroom  before coming up with the present combination of "bicubic" and "bicubic smoother".

Best regards
Erik


I bet Canon and Nikon and others are more worried about the unwashed masses seeing ugly moire on the bride's dress than squeezing marginal amounts of sharpness. Sharpening is one slider for most people, but fixing moire in post requires more effort.

I understand moire becomes less of an issue the more resolution there is, though. Does that hold even for down-rezzed pics? As more and more photography never leaves the computer screen, moire might be an issue for years.
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hjulenissen

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Re: Is it past time to say goodbye to the AA filter?
« Reply #10 on: September 16, 2011, 04:12:15 am »

It is interesting how we always end up trusting our eyes better than science.  ;D
Perhaps it is the application of similarity measure used in scientific approaches that simply does not apply all too well when images will be viewed by humans?

Sampling theory tells us that an analog waveform can be losslessly recovered if it is prefiltered to a bandwidth < fs/2 (if the signal is bandpass, the filter can be bandpass as well, but commonly it will be lowpass). This means that for waveforms of larger bandwidth, there will be some loss of resolution (due to prefiltering). Does this mean that Nyquistian brick-wall pre/post-filtering enclosing a point-sampler is the one and only way to discretize a waveform? Perhaps some horribly complex integration of knowledge about filtering, sampling, waveform will give a more "optimal" use of resources (in e.g. the least squares sense)?

It seems that acutance or "sharpness" is really important to humans in deciding if a scene looks "pleasing" or realistic. Even to the degree that "false" acutance, or sharp edges that are misplaced by a small amount can look better than smooth, non-aliased edges. Current OLPF seems to trade some aliasing vs some loss of sharpness. That may be Canon and Nikons interpretation of how to make good images at a reasonable cost and level of user-intervention.

-h
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Bart_van_der_Wolf

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Re: Is it past time to say goodbye to the AA filter?
« Reply #11 on: September 16, 2011, 04:38:59 am »

It is interesting how we always end up trusting our eyes better than science.  ;D

From a signal processing standpoint, it sounds clear that the lack of AA filter results in images that are intrinsically flawed in that they create information that was simply not there in the initial scene. That is regardless of the fact that these information "seem" real.

The example of the resolution chart of Erick is totally clear on this one. These images are full of fake details that seem sharp but simply are not true.

Hi Bernard,

Do understand that such aliasing is an ideal manifestation of the phenomenon, because it happens to look similar to the real detail. Stairstepped edges (and hair like stuctures), corrupted tile roofs and brick roads/walls, hard to rescue fabric, false color moiré, etc., etc., are more common manifestations. Erik also showed an example of a (Samuel Smith) label on a bottle, it is very difficult to rescue. Those images are sometimes also hard to enlarge, because the artifacts become more visible.

Cheers,
Bart
« Last Edit: September 16, 2011, 04:41:31 am by BartvanderWolf »
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Bart_van_der_Wolf

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Re: Is it past time to say goodbye to the AA filter?
« Reply #12 on: September 16, 2011, 05:06:59 am »

Bart,
The manufacturers know the nature of the AA filters that they use, so it strikes me that they would know the best way to deconvolve the filter.  Why is it that they don't have this sharpening automatically done in their raw conversion software?

Probably because there is no free lunch. Deconvolution can also increase noise and it requires a bit of processing power. Therefore sharpening becomes more complicated that just using a slider. I'm not sure if the Canon DPP application does not use deconvolution of some sort, because it is quite effective when sharpening low noise Raw conversions. I don't know the Nikon offerings well enough to comment.

Quote
From personal experience, I hate that the Nikon D3X always seems to overdo the AA.  I have tried a few sharpeners with deconvolution (some type of Richardson-Lucy), but some are no longer supported on current operating systems, and none have really done the trick.  I much prefer the files I get from MFDB.

Do note that there are more differences in MFDB images than just the lack of an AA-filter. Larger magnification on the sensor due to the longer focal lengths also results in better utilization of the system MTF response. Less output magnification also allows to hide some issues. Also note that some backs, generally the lower MP count ones, are notoriously poor choices for e.g. fashion (fabric) photography. On the other hand, the potentially shallower DOF may help reduce aliasing in OOF areas, and stopping down will create more diffraction which can also do some AA-filtering. The aliasing tendencies of MFDB images cannot be directly compared to those in 35mm full frame sensors. The smaller sensors require more precautions to avoid magnified artifacts.

Cheers,
Bart
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Colin4May

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Re: Is it past time to say goodbye to the AA filter?
« Reply #13 on: September 21, 2011, 06:00:35 am »

I read this thread with some trepidation!

I am a rank amateur who recently got a Lumix G3, after watching this advert.  http://www.panasonic.co.uk/html/en_GB/Products/LUMIX+Digital+Cameras/Overview/LUMIX+G+Micro+System+Cameras/4855154/index.html
 I thought it was fine, but am now worried in case i have got a camera which is a bit retro?

I guess i should just take it for what it is and what i want to use it for (macro photography of insects, flowers etc). But is this AA filter thing at all relevant to what I am using my camera for, or can i just sleep easy at night, in the knowledge that it doesn't apply to me?

Thanks! :o
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Bart_van_der_Wolf

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Re: Is it past time to say goodbye to the AA filter?
« Reply #14 on: September 21, 2011, 07:52:25 am »

I read this thread with some trepidation!

I am a rank amateur who recently got a Lumix G3, after watching this advert.  http://www.panasonic.co.uk/html/en_GB/Products/LUMIX+Digital+Cameras/Overview/LUMIX+G+Micro+System+Cameras/4855154/index.html
 I thought it was fine, but am now worried in case i have got a camera which is a bit retro?

Retro? Just because Panasonic chose to reduce the risk of aliasing related artifacts by using an AA-filter (which is therefore common practice in the industry)?

Quote
I guess i should just take it for what it is and what i want to use it for (macro photography of insects, flowers etc). But is this AA filter thing at all relevant to what I am using my camera for, or can i just sleep easy at night, in the knowledge that it doesn't apply to me?

I wouldn't let the presence of an AA-filter spoil the fun of using what seems to be a very nice camera (technical review/comparison). In general it is useful to have a decent sharpening method available for the final output, and there are a few solutions available (depending on the software one uses). For best quality it also is good to shoot Raw rather than JPEG, and that will allow to do one's own sharpening rather than depend on the camera's implementation as it will be used on JPEGs.

Cheers,
Bart
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feppe

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Re: Is it past time to say goodbye to the AA filter?
« Reply #15 on: September 21, 2011, 12:28:37 pm »

I read this thread with some trepidation!

I am a rank amateur who recently got a Lumix G3, after watching this advert.  http://www.panasonic.co.uk/html/en_GB/Products/LUMIX+Digital+Cameras/Overview/LUMIX+G+Micro+System+Cameras/4855154/index.html
 I thought it was fine, but am now worried in case i have got a camera which is a bit retro?

I guess i should just take it for what it is and what i want to use it for (macro photography of insects, flowers etc). But is this AA filter thing at all relevant to what I am using my camera for, or can i just sleep easy at night, in the knowledge that it doesn't apply to me?

It does apply, but has only a marginal impact on overall image quality, and most of it can be fixed with prudent sharpening. MFT cameras have in my experience weaker AA filter than most DSLRs, although I'm not familiar with G3 but it's supposed to be an outstanding camera. There are many threads about AA filters, which often make it sound like camera manufacturers put a "make your pictures look crappy" filter on all their cameras, which is patently false.

If you get worked up about it, soon you'll start reading the MFDB forum and realize you need at least 100 megapixels, 1000+ euro tripod, 1000+ euro geared head, several thousands of euros worth of lighting, and a camera which costs more than two new medium-sized cars. Lenses are extra. And if you think I'm joking, go there and have a look. But you've been warned :)
« Last Edit: September 21, 2011, 12:30:43 pm by feppe »
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feppe

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Re: Is it past time to say goodbye to the AA filter?
« Reply #16 on: September 21, 2011, 12:29:50 pm »

Retro? Just because Panasonic chose to reduce the risk of aliasing related artifacts by using an AA-filter (which is therefore common practice in the industry)?

Not only common practice; AA filterless cameras are a rare exception.
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