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Author Topic: Absurd DxO D800E results: Are low pass filters a joke?  (Read 18261 times)

ErikKaffehr

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Re: Absurd DxO D800E results: Are low pass filters a joke?
« Reply #60 on: May 28, 2014, 02:09:10 pm »

Hi,

I would agree on most issues. Placebo effects may play a role. Also, sharpening very clearly plays a very major role.

Something I have noticed is that there can be very little difference in moderately small prints, like A2, between formats and megapixels. Once a format is good enough, we get diminshing returns. For instance a smaller format may give better DoF that may be preferable to the shallower DoF of the larger format.

Having more megapixels doesn't really hurt anything else, so I guess it is always a good thing, at least within reasonable limits.

Best regards
Erik

We should all know by now that expectations can result in a placebo effect, on all matters, whether it be testing the efficacy of a new drug, or the clarity and 3-dimensionality of a hi-fi or a photographic image experience.

To resolve such matters you need the double blind test. That is, a comparison in which the viewers or listeners have no knowledge of the credentials, brand, or model of the equipment being used to produce the sound or images.

In the world of hi fi, such testing has produced remarkable results. Subtleties of amplifier harmonic distortion often get drowned in the larger deficiencies of loudspeaker performance and room acoustics, often resulting in expensive amplifiers with ultra-low harmonic distortion serving no practical purpose.

Likewise, subtleties of resolution differences in images can get lost depending on print size and viewing distance.

Without a direct comparison, at very large sizes, of D800 and D800E images of the same subject using the same lens and shooting methodology, there can be no meaningful conclusion.
Such comparisons would of course have to include unsharpened images, as well as images sharpened with a variety of different techniques and programs.

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Jim Kasson

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Re: Absurd DxO D800E results: Are low pass filters a joke?
« Reply #61 on: May 28, 2014, 02:29:42 pm »

Having more megapixels doesn't really hurt anything else, so I guess it is always a good thing, at least within reasonable limits.

...assuming excellent down-resing algorithms, which is not always the case.

Jim
« Last Edit: May 28, 2014, 02:50:47 pm by Jim Kasson »
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ErikKaffehr

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Re: Absurd DxO D800E results: Are low pass filters a joke?
« Reply #62 on: May 28, 2014, 02:45:02 pm »

Jim,

Thanks for making that point! Very true, indeed.

On the other hand, I would suppose that resizing an image is always prone aliasing, except special cases, so just having more pixels would not exaggerate the problem.

Best regards
Erik

Having more megapixels doesn't really hurt anything else, so I guess it is always a good thing, at least within reasonable limits./quote]

...assuming excellent down-resing algorithms, which is not always the case.

Jim
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Jack Hogan

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Re: Absurd DxO D800E results: Are low pass filters a joke?
« Reply #63 on: May 29, 2014, 03:34:02 am »

Hi Jack

That's very interesting information you've provided.

Thanks Dave, I owe it mostly to Frans van den Bergh, Detail Man (at DPR) and The_Suede.

Quote
The AA blur in one direction only is interesting but I'm struggling to understand the rationale behind it !

In addition to Bart's suggestion, here is what The_Suede had to say about it.

Jack
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Jack Hogan

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Re: Absurd DxO D800E results: Are low pass filters a joke?
« Reply #64 on: May 29, 2014, 04:39:03 am »

It is just that I consider capture sharpening (preferably by deconvolution) as an essential part of the process, especially if there is an AA filter. I understand it is difficult to include it in a comparative test and not cause more controversy.

Hi Francisco,

I agree that capture sharpening is an essential part of the image formation process.  It's however not necessary in some situations, and it may be detrimental in others.  I think it's useful to distinguish between two categories of questions:

1) How will lens A perform compared to lens B on my one camera?; and
2) How will lens A perform on two different cameras with varying AA strengths and most other things equal?

In the first case a metric to help with buying decisions should imo concentrate on the hardware only.  As a (amateur landscape) photographer I consider the job to capture the best spatial information possible at the scene so that such information can be later processed to provide the most pleasing results when viewed on the final display medium as desired. The better the information captured, the better the final result.  The best spatial information captured is obtained by using the best hardware available, so what I am interested in is the objective performance of the hardware in a camera system when selecting equipment - as opposed to subjective post processing workflow results (including demosaicing and sharpening algorithms with arbitrary parameters) which can always (and mostly will) be added later to obtain the desired effect.  Perhaps this leaves open a question of diminishing returns past a certain point, but that's one I am willing to deal with.

In the second case I can see the rationale for applying capture sharpening before spatial resolution measurements because it is true that one may be able to 'restore' some of the effects of a stronger AA filter or other subsystem through the judicious application of advanced sharpening algorithms.  On the other hand things get very fuzzy and subjective very quickly because perception enters the equation prominently.  Plus we all know that typical sharpness metrics are very sensitive to acutance, whether that be due to the real performance of the system or introduced artificially by an overzelous operator.  It doesn't take much.

Take for instance Photozone.de which opens images for MTF measurements in ACR/LR with sharpening at default, what most observers would consider mild capture sharpening.  Edge Spread Function profiles so generated show overshoots and undershoots in what in the physical world is actually a monotonically increasing S-shaped curve.  Even that is too much.  Perhaps a reasonable criterion for how much capture sharpening to apply should be that physical limits not be exceeded.  Easier to say than to do.  Or perhaps the operator should sharpen both images to the best of his subjective evaluation/abilities following a strict set of criteria.  Again...  And this says nothing of the amplified noise and introduced artifacts that such an approach would entail.

Too many balls in the air for my taste.  So while I see the rationale for the application of capture sharpening before measuring spatial resolution for some uses, I have a really hard time figuring out how such measurements can be practically useful by themselves.  That's why I tend to start at Lenstip.com (mostly hardware), move on to Photozone.de (capture sharpened) before reaching DxO (perceptual milk shake) and then drawing my own Jack-Pix purchasing conclusions :-)

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Dave Ellis

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Re: Absurd DxO D800E results: Are low pass filters a joke?
« Reply #65 on: May 29, 2014, 05:08:36 am »

Thanks for the links Jack. I have come across Frans' work before and have played with MTFMapper. He produces some good stuff.

I had a quick look at The_Suede's comments (where do they get these User Names !!). Interesting point he makes about line skipping when reading out video.

Dave

Thanks Dave, I owe it mostly to Frans van den Bergh, Detail Man (at DPR) and The_Suede.

In addition to Bart's suggestion, here is what The_Suede had to say about it.

Jack
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eronald

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Re: Absurd DxO D800E results: Are low pass filters a joke?
« Reply #66 on: May 29, 2014, 09:37:12 am »

An interesting question is whether real world images correspond to the tests. Does the fact that I can capture-sharpen a 100 ISO perfectly exposed image realistically reflect the noise explosion I will get when I do the same to a 6400 ISO shot?

And by the way, what exactly is acutance?

Edmund

Hi Francisco,

I agree that capture sharpening is an essential part of the image formation process.  It's however not necessary in some situations, and it may be detrimental in others.  I think it's useful to distinguish between two categories of questions:

1) How will lens A perform compared to lens B on my one camera?; and
2) How will lens A perform on two different cameras with varying AA strengths and most other things equal?

In the first case a metric to help with buying decisions should imo concentrate on the hardware only.  As a (amateur landscape) photographer I consider the job to capture the best spatial information possible at the scene so that such information can be later processed to provide the most pleasing results when viewed on the final display medium as desired. The better the information captured, the better the final result.  The best spatial information captured is obtained by using the best hardware available, so what I am interested in is the objective performance of the hardware in a camera system when selecting equipment - as opposed to subjective post processing workflow results (including demosaicing and sharpening algorithms with arbitrary parameters) which can always (and mostly will) be added later to obtain the desired effect.  Perhaps this leaves open a question of diminishing returns past a certain point, but that's one I am willing to deal with.

In the second case I can see the rationale for applying capture sharpening before spatial resolution measurements because it is true that one may be able to 'restore' some of the effects of a stronger AA filter or other subsystem through the judicious application of advanced sharpening algorithms.  On the other hand things get very fuzzy and subjective very quickly because perception enters the equation prominently.  Plus we all know that typical sharpness metrics are very sensitive to acutance, whether that be due to the real performance of the system or introduced artificially by an overzelous operator.  It doesn't take much.

Take for instance Photozone.de which opens images for MTF measurements in ACR/LR with sharpening at default, what most observers would consider mild capture sharpening.  Edge Spread Function profiles so generated show overshoots and undershoots in what in the physical world is actually a monotonically increasing S-shaped curve.  Even that is too much.  Perhaps a reasonable criterion for how much capture sharpening to apply should be that physical limits not be exceeded.  Easier to say than to do.  Or perhaps the operator should sharpen both images to the best of his subjective evaluation/abilities following a strict set of criteria.  Again...  And this says nothing of the amplified noise and introduced artifacts that such an approach would entail.

Too many balls in the air for my taste.  So while I see the rationale for the application of capture sharpening before measuring spatial resolution for some uses, I have a really hard time figuring out how such measurements can be practically useful by themselves.  That's why I tend to start at Lenstip.com (mostly hardware), move on to Photozone.de (capture sharpened) before reaching DxO (perceptual milk shake) and then drawing my own Jack-Pix purchasing conclusions :-)


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Manoli

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Re: Absurd DxO D800E results: Are low pass filters a joke?
« Reply #67 on: May 29, 2014, 11:27:03 am »

And by the way, what exactly is acutance?

Good to see you back, Edmund, on form and clearly fully recovered ...

M
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ErikKaffehr

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Re: Absurd DxO D800E results: Are low pass filters a joke?
« Reply #68 on: May 29, 2014, 12:42:34 pm »

+1


Regarding acutance:
http://en.wikipedia.org/wiki/Acutance

Best regards
Erik

Good to see you back, Edmund, on form and clearly fully recovered ...

M
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Manoli

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Re: Absurd DxO D800E results: Are low pass filters a joke?
« Reply #69 on: May 29, 2014, 12:55:43 pm »

Regarding acutance:
http://en.wikipedia.org/wiki/Acutance

Dear Erik,

Knowing Edmund (from his posts) ,  I don't think it was entirely a serious question ...
In fact, I wouldn't be surprised if he had written the Wikipedia entry himself !

Best,
M
« Last Edit: May 29, 2014, 01:03:56 pm by Manoli »
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ErikKaffehr

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Re: Absurd DxO D800E results: Are low pass filters a joke?
« Reply #70 on: May 29, 2014, 02:37:17 pm »

Hi,

I know Edmund from his postings…

On the other hand I feel that the definition of acutance is a bit fuzzy az are many terms used to describe the more or less esoteric qualities of imaging systems. The more esoteric the quality the more fuzzy the definition…

So I feel that Edmunds question may be a retorical one but it is still a good one!

Best regards
Erik


Dear Erik,

Knowing Edmund (from his posts) ,  I don't think it was entirely a serious question ...
In fact, I wouldn't be surprised if he had written the Wikipedia entry himself !

Best,
M
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Erik Kaffehr
 

Telecaster

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Re: Absurd DxO D800E results: Are low pass filters a joke?
« Reply #71 on: May 29, 2014, 03:42:31 pm »

IMO noise explosions can be just as creatively valid in photography as in music.  ;)

-Dave-
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eronald

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Re: Absurd DxO D800E results: Are low pass filters a joke?
« Reply #72 on: May 29, 2014, 05:59:10 pm »

Dear Erik,

 I wouldn't be surprised if he had written the Wikipedia entry himself !

Best,
M

Damning with faint praise. Just saw that, I think that entry is a nice start, but it might need some more love, even polyamory :)

Edmund
« Last Edit: May 29, 2014, 06:01:44 pm by eronald »
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dreed

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Re: Absurd DxO D800E results: Are low pass filters a joke?
« Reply #73 on: May 30, 2014, 01:09:26 pm »

The point of a low pass filter is to cut off at a certain max frequency. Instead, it seems the D800 filter just chops 25% or so off the measured resolution (whatever that means) of each lens.

This happens with every DSLR that has an AA/OLPF in front of the sensor and in some cases gets into the 30%+ range.
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