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Author Topic: removing the AA filter  (Read 104790 times)

Graeme Nattress

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removing the AA filter
« Reply #40 on: October 19, 2007, 06:22:56 pm »

Even for landscape shots you can need a good AA - grass, in a field as it heads off into the distance will alias quite badly without one.

Graeme
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John Sheehy

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« Reply #41 on: October 19, 2007, 07:13:32 pm »

Quote
Even for landscape shots you can need a good AA - grass, in a field as it heads off into the distance will alias quite badly without one.
[a href=\"index.php?act=findpost&pid=147288\"][{POST_SNAPBACK}][/a]

What's the problem?  You don't like blades of grass that come in integer widths, and look like Tetris pieces?
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marcmccalmont

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removing the AA filter
« Reply #42 on: October 19, 2007, 09:21:54 pm »

FYI attached are 3 in-camera Jpegs with no post processing just size reduction in PS. 5D (no AA filter) 70-200mm2.8 IS. Nothing special just thought you might want to see.
Marc

[attachment=3614:attachment][attachment=3613:attachment][attachment=3615:attachm
ent]
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Marc McCalmont

John Sheehy

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removing the AA filter
« Reply #43 on: October 19, 2007, 11:42:53 pm »

Quote
FYI attached are 3 in-camera Jpegs with no post processing just size reduction in PS. 5D (no AA filter) 70-200mm2.8 IS. Nothing special just thought you might want to see.
[a href=\"index.php?act=findpost&pid=147304\"][{POST_SNAPBACK}][/a]

Downsized images only distinguish between aliased and non-aliased images by the low-frequency aliasing which may be present, but isn't in this image.

The aliasing obvious in the focused grass area could be obtained *with* an AA filter, and poor downsizing.  Do you think that the emphasis on the 45 degree aspects of the grass in the focused area is a good thing?  I find it quite annoying, myself.
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marcmccalmont

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removing the AA filter
« Reply #44 on: October 19, 2007, 11:55:02 pm »

An artifact of bicubic sharper?
Marc
[attachment=3619:attachment]
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Marc McCalmont

ErikKaffehr

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removing the AA filter
« Reply #45 on: October 20, 2007, 02:33:03 am »

Hi,

There are quite few answers.

1) MF backs do suffer from moire effects
2) Stopping down acts like a AA-filter, because of diffraction
3) High resolution backs have less problems with moire than low resolution backs
4) Lens resolving power does matter, I would suggest that MF-format lenses have less resolving power than premium class 135 lenses. You can check this comparing the "Photodo MTF ratings on:
http://www.photodo.com/products.html?mount...e=Hasselblad+CF
and
http://www.photodo.com/products.html?mount...me=Canon+EF+USM
5) What you photograph does matter
6) How much time you spend on each image in Photoshop matters.

Unfortunately I don't possess an MF digital back, even if I have MF equipment for film, so I don't talk from own experience. Generally speaking you get aliasing when the resolution of the lens exceeds the resolution of the sensor. So what the AA filter does is to reduce resolution. The same can be achieved by stopping down or defocusing. The only situation when you can get problem with moiré is if you are shooting at optimum (medium or large) aperture, have some material having regular structure  in the focus plane and using an excellent lens.

Another effect caused by aliasing is that thin branches or twigs on trees can show pixelation or colored pixels. With the APS-C cameras I'm shooting with I have never seen any moire in real life pictures, but they do have AA-filters.


Best regards
Erik


Quote
You may want to look at this thread for more discussion on this topic

http://luminous-landscape.com/forum/index....opic=20081&st=0

Would someone like to perhaps enlighten me on why most medium format backs seem to forgo the AA filter?
and medium format backs are held up as the holy grail of image quality
[a href=\"index.php?act=findpost&pid=145765\"][{POST_SNAPBACK}][/a]
« Last Edit: October 20, 2007, 02:47:05 am by ErikKaffehr »
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jing q

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removing the AA filter
« Reply #46 on: October 20, 2007, 02:39:01 am »

Quote
FYI attached are 3 in-camera Jpegs with no post processing just size reduction in PS. 5D (no AA filter) 70-200mm2.8 IS. Nothing special just thought you might want to see.
Marc

[attachment=3614:attachment][attachment=3613:attachment][attachment=3615:attachm
ent]
[a href=\"index.php?act=findpost&pid=147304\"][{POST_SNAPBACK}][/a]

goddammit stop tempting me!
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Ray

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removing the AA filter
« Reply #47 on: October 20, 2007, 05:13:55 am »

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That's a perfect image to show how the aliases fold back to a lower spatial frequency, and hence cannot now be removed by a blur, other than a blur so large that ruins the image and removes all the detail in it. There's no way known to repair an image like that and remove it's aliases.

Graeme
[a href=\"index.php?act=findpost&pid=147088\"][{POST_SNAPBACK}][/a]

I don't believe the image shows specifically how the aliasing folds back to a lower spatial frequency, just that it has in this example.

I presume that for best results, moire effects should be tackled at the RAW image stage if possible.
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John Sheehy

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removing the AA filter
« Reply #48 on: October 20, 2007, 08:19:49 am »

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I don't believe the image shows specifically how the aliasing folds back to a lower spatial frequency, just that it has in this example.

I presume that for best results, moire effects should be tackled at the RAW image stage if possible.
[a href=\"index.php?act=findpost&pid=147345\"][{POST_SNAPBACK}][/a]

They are best tackled at the optical state.
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John Sheehy

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removing the AA filter
« Reply #49 on: October 20, 2007, 08:20:57 am »

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goddammit stop tempting me!
[a href=\"index.php?act=findpost&pid=147332\"][{POST_SNAPBACK}][/a]

Any camera can give that so-called "3D pop" in a downsized image like that, with the "right" method.
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Graeme Nattress

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removing the AA filter
« Reply #50 on: October 20, 2007, 09:22:10 am »

I don't think bicubic is a good downsampling filter. Gaussian is "safe" in terms of aliasing, usually, but if you want some visuals on it, http://www.cambridgeincolour.com/tutorials...ize-for-web.htm shows a few examples.

Graeme

Quote
An artifact of bicubic sharper?
Marc
[attachment=3619:attachment]
[a href=\"index.php?act=findpost&pid=147320\"][{POST_SNAPBACK}][/a]
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Tim Gray

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removing the AA filter
« Reply #51 on: October 20, 2007, 10:21:51 am »

Quote
I don't think bicubic is a good downsampling filter. Gaussian is "safe" in terms of aliasing, usually, but if you want some visuals on it, http://www.cambridgeincolour.com/tutorials...ize-for-web.htm shows a few examples.

Graeme
[a href=\"index.php?act=findpost&pid=147378\"][{POST_SNAPBACK}][/a]


It's sometimes tough to figure out what folks are really trying to say.  When I saw the post from marcmccalmont and looked at the attached crop, I naturally figured that he was being a bit tongue in cheek with his "bicubic" comment, since (at least to me) the shoe was a clear moire example in a shot posted to demonstrate how having no filter wasn't a problem (forgive the double negative)
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marcmccalmont

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removing the AA filter
« Reply #52 on: October 20, 2007, 02:24:18 pm »

Don't read anything into my posts.  I'm not smart enough to send hidden messages. The pictures were not intended to be an endorsement to remove your AA filter or not. Just information for those who do not have a camera without a AA filter or experience with one. I believe that for nature and landscapes (random patterns) a AA filter is a hindrance to sharpness. For fashion photography the moiré would be unlivable. For everything in between the camera manufacturers have decided to install one (I think a conservative approach). I personally feel that theory is great but empirical data is more relevant. Practical use has a lot of validity. It is also hard to judge things with low resolution and Jpeg artifacts. The un-compressed 16 bit Tiffs printed on my iPF5000 look much better but I can't show you those. BTW in the crop I don't see the 45 degree moiré in the grass or moiré in Coaches shoes, the pattern is the stitching, the socks look pretty good to me too. What I do like is the 3D pop that the camera has that was not as apparent with the AA filter and the increased sharpness. I would like to see DSLR’s with replaceable AA filters so you can have your cake and eat it too, maybe even IR photography as an option.
Marc
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Marc McCalmont

marcmccalmont

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« Reply #53 on: October 20, 2007, 02:37:16 pm »

Quote
I don't think bicubic is a good downsampling filter. Gaussian is "safe" in terms of aliasing, usually, but if you want some visuals on it, http://www.cambridgeincolour.com/tutorials...ize-for-web.htm shows a few examples.

Graeme
[a href=\"index.php?act=findpost&pid=147378\"][{POST_SNAPBACK}][/a]

Interesting link. Is there an easy way to use other algorithms inside of photoshop?
marc
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Marc McCalmont

juicy

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removing the AA filter
« Reply #54 on: October 21, 2007, 10:55:15 am »

Quote
An artifact of bicubic sharper?
Marc
Attached Image

I haven't yet seen bicubic-induced color-moire in black socks... So maybe it's something else.  

Cheers,
J
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juicy

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« Reply #55 on: October 21, 2007, 11:28:45 am »

Hi!

There were couple of interesting threads about mfdbs and moire issues with sharp lenses about half a year ago in LL with very good example shots. For example: http://luminous-landscape.com/forum/index....topic=13563&hl=

Cheers,
J
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Phil Indeblanc

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removing the AA filter
« Reply #56 on: January 04, 2010, 03:09:36 am »

Quote from: nma
The democarcy of these forums is that everyone's opinion is equal. But not all of them are correct.  With digital imaging, we are not entiltled to infinite resolution; the attainable resolution is limited by the sampling frequency of the sensor, not the lens.  In fact, if you ignore this inconvenient truth, you get aliasing. Aliasing of periodic elements,such as fabrics, are called Moire patterns. The image is distorted, with high frequency details in the wrong location. There is no such thing as color Moire patterns. The  sampling problem for Bayer sensors is complicated by the different sampling frequencies of the red, blue and green detector elements. Once this distortion is observed in an image, there is no sure way to remove it unless you know what the image is supposed to look like. In other words there can sometimes be mitigation of the effect but there  is no general method to remove aliasing.  

The AA fiter is there to attenuate high frequency information beyond that which can be faithfully recorded by the sensor. It is digital imaging 101 to roll off the high frequency information above the Nyquist frequency of the sensor. This is THE standard approach in digital signal processing. No amount of voting or opinion is going to change this. One goes naked at their own peril. In digital photography, the roll off of the high frequency information is done by blurring the image before it reaches the detector with an AA filter. In paractice, AA filters may not be perfect. The goldilocks effect would be not too weak to allow aliasing and not too strong to remove any detail.  With the AA filter it is generally helpful to apply a small amount of sharpening during raw conversion.  

Arguing, for example, that the Leica M8 is better because it lacks an AA filter, is a hypothesis. There is no proof. It might be some other element in their proprietary development. To prove it is the lack of an AA filter one needs to make measurements with an M8, with and without an AA filter. Measurements, not pictures shot out your porch window that are later displayed as jpegs on a computer monitor.

Sorry fot the rant, but this same subject has just been explored in Cameras, Lenses and Shooting gear.


I don't know what your theories or hypothesis mean. You sound like some informed smart scienticfic dude, but simply...you are wrong. Period. tested and proven.  lack of AA delivers sharper, more "3d" images.  AA evens things out.  Tested and done.

Only problem with the service is that they can only remove 1 of the 2 filters, so it is still not as sharp as MF, or non AA sensors.  That is likely why the compared images are not that obviouse of a difference.
« Last Edit: January 04, 2010, 03:16:30 am by Phil Indeblanc »
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nma

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removing the AA filter
« Reply #57 on: January 04, 2010, 09:11:51 pm »

Quote from: Phil Indeblanc
I don't know what your theories or hypothesis mean. You sound like some informed smart scienticfic dude, but simply...you are wrong. Period. tested and proven.  lack of AA delivers sharper, more "3d" images.  AA evens things out.  Tested and done.

Only problem with the service is that they can only remove 1 of the 2 filters, so it is still not as sharp as MF, or non AA sensors.  That is likely why the compared images are not that obviouse of a difference.


Phil,

You seem angry. Why?  What proof is there that removing the 2nd AA filter will make the images as sharp as "tested and proven?" You concede that removing one does not provide an impressive result. Showing an image on a web page is not proof. Show me measurements that demonstrate that resolution is improved without artifact.

The interesting thing is that the effect of a well  deigned AA filter should diminish as the digital sampling (more mega pixels) increases, until the system is limited by the lens. None of the discussants has observed this effect. Why? Are there other factors that are not considered?

I can imagine building a sensor which is over sampled to the extent that the lens will always be the limiting element. Then the AA filter could be removed and the image could be resampled in the camera and then stored. The highly sampled image will have more noise at each pixel but the resampled image will have the noise level consistent with the lower sampling, just no aliasing.

There is no free lunch. The ultimate resolution of the system is determined by the sampling of the sensor; there is no way to do better. If you remove the AA filter the distortions in the image will be visible when high resolution lenses are used. In fact, these distortions will be present in all images, not just those containing period structures. Details at a spatial frequencies above Nyquist will be rendered at lower frequencies. These distortions cannot be removed by software algorithms.
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Phil Indeblanc

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« Reply #58 on: January 04, 2010, 11:18:22 pm »

I don't mean to come across as angry.  I do see often in forums with people of high degree and regard in the science of optics or theories or mathmetics, ...sometimes negating statements, just because it doesn't make sense on their fact list, etc.

I have used a 1Ds Mk1, and 1DsMk2, and the Kodak SLRc with Leica glass that is sharper than all the Canon L macro lens'.  I tested them on a studio stand with the fixed lens on the mount, swapping the bodies..... and the difference is clearly in the image. I don't think I have those exact test samples as it was done for me to know what to work with.  I would be willing to do a sample for you.  

On that note...Although my Kodak file had a sense of MF quality/razor sharpness, the sensor does not handle differnt light setups well.  I would think this is something that has been addressed at some point in the 6 or 7 or so years on sensor dev. So I use a mfdb.  I recently used it knowing the lighting would work, and I do have a image from it, but nothing to compare it with.


I don't really know well this relation you explain between sensor and resolving power of the lens = needing a AA filter, but....

Maybe it is time for either Canon or Nikon to buy out the Foveon technology?
« Last Edit: January 04, 2010, 11:35:17 pm by Phil Indeblanc »
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ErikKaffehr

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« Reply #59 on: January 05, 2010, 12:26:20 am »

Hi,

The issue is always complicated by the need of sharpening. An AA-filtered image needs and can take much more sharpening than an unfiltered image.

Regarding the Foevon it would actually just make things worse. It has relatively low resolution so it really needs AA-filtering.

Check this image (from a Sigma DP2)
http://a.img-dpreview.com/reviews/SigmaDP2...res_ACR-003.JPG

You can observe several inversions of contrast, albeit it's very contrasty. But it shows black lines where they should be white and vice versa.

So the image may be pleasant to the eye but it's mostly artifacts.

The image below is correctly resolved (but much softer)

http://a.img-dpreview.com/reviews/SigmaDP2...III_ACR-003.JPG

Best regards
Erik

Quote from: Phil Indeblanc
I don't mean to come across as angry.  I do see often in forums with people of high degree and regard in the science of optics or theories or mathmetics, ...sometimes negating statements, just because it doesn't make sense on their fact list, etc.

I have used a 1Ds Mk1, and 1DsMk2, and the Kodak SLRc with Leica glass that is sharper than all the Canon L macro lens'.  I tested them on a studio stand with the fixed lens on the mount, swapping the bodies..... and the difference is clearly in the image. I don't think I have those exact test samples as it was done for me to know what to work with.  I would be willing to do a sample for you.  

On that note...Although my Kodak file had a sense of MF quality/razor sharpness, the sensor does not handle differnt light setups well.  I would think this is something that has been addressed at some point in the 6 or 7 or so years on sensor dev. So I use a mfdb.  I recently used it knowing the lighting would work, and I do have a image from it, but nothing to compare it with.


I don't really know well this relation you explain between sensor and resolving power of the lens = needing a AA filter, but....

Maybe it is time for either Canon or Nikon to buy out the Foveon technology?
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