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Author Topic: AA-filtering CCD and CMOS  (Read 19857 times)
Slough
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« Reply #120 on: October 16, 2009, 04:05:44 AM »
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Quote from: ejmartin
Speaking as a scientist, that's bullshit  

The test Erik proposes would be, "how do cameras B and C compare when their RAW data are subjected to identical manipulations", not "how do cameras B and C compare when treated in uncontrolled different ways?" as you seem to prefer.   If the converter is a potential source of bias, then it is better to use a family of converters on each camera to eliminate that bias, so long as it is known that any converter used applies the same process to any given RAW file.  However, since only dcraw is open source, that's hard to verify for any other converter.  RAW conversion is not a black art, which needs sympathetic vibes between conversion algorithm and camera.

Depends. If you are trying to analyse something inherent in each camera, then yes use the same RAW converter. That way you minimise the number of different variables. But if you want an answer that applies to the real world, such as "Which camera is capable of the best resolution and lowest artifacts", then choose the optimal RAW converter for each. After all, when someone buys camera A, will the clouds part to reveal an elderly gentleman who goes on to say in a deep voice "Though shalt only use converter X with that camera, as should have been decreed by Moses, but he missed that one off his list due to a poor retention span and forgetting to make notes, even though I warned him 11 commandments was an awful lot to remember, what with the excitement of meeting his God for the first time, oh well, now where was I, oh yes, I must get back to that game of mah jong with Beelzebub".
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bjanes
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« Reply #121 on: October 16, 2009, 07:54:40 AM »
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Quote from: telyt
Would you compare an E-6 film and a C-41 film using XTol as a developer, and then conclude anything meaningful about the films' performance?

The problem with the test Eric proposes is that different camera systems require different manipulations to get the most out of the system.  different color profiles, and different capture sharpening for example.  What's the purpose of the test?  It it to compare camera systems?  if so limiting the test to a single converter provides only scanty information, and unfortunately the unscientific voices on the internet (and there are a few of these   ) don't recognize the difference between a test limited to a single converter and a comprehensive test.

An uncontrolled test, BTW, would involve applying random converters to equally random cameras' files.  You have mis-represented my position.  What I'm suggesting is that in order to compare optimum performance of two or more camera systems, optimize each system first then compare, otherwise the test's conclusion will more than likely be erroneous.

Doug,

Have you actually used your extended optimization procedure for any two or more cameras with systematic manipulation of the raw converter settings for each of multiple raw converters? If so, I'm surprised that you have time to participate in this thread. As you know, raw converters usually have defaults that differ for each individual camera, and these may not be optimum for the given camera. Controlling all these variables would be a daunting task and you would still have uncontrolled variables. We are discussing aliasing, and the lens is an important factor: if the lens can't resolve above Nyquist, there will be no aliasing. What is the optimum f/stop for each lens? Do you use the same lens for all cameras? Some raw converters correct lens aberrations for their brand of camera with certain of their lenses. Sharpening is also critical, since cameras with blur filters require more sharpening than cameras lacking them. Different raw converters have different sharpening.

I don't know your background, and your understanding of the scientific method, but I would remind you that Emil is professor of physics at one of our best research institutions (the University of Chicago) and he knows more about the scientific method and experimental design than most of us. Personally, I give his posts a great deal of weight as compared to those by persons unknown to me.

As Emil suggests, it might be prudent to test with a number of well regarded raw converters to determine how significant this variable is. If the results are similar or can be correlated, you might decide to settle on one raw converter. This is the approach of most testers who post results on the net. If you get the best results with the camera maker's raw converter, you still do not know if these good results are due to the camera or raw converter (which does not support any other brand of camera).



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thierrylegros396
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« Reply #122 on: October 16, 2009, 08:19:31 AM »
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To make good comparisons, we need first a well accepted definition of "optimum sharpening" and means to check it.

Sometimes I'm amazed with definition graph with a lot of "moiré" and other artifacts, and people who are able to tell : 2300 LPH absolute resolution.

So yes we first need a well accepted repetitive procedure !


Have a Nice Day.

Thierry
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bjanes
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« Reply #123 on: October 16, 2009, 08:22:44 AM »
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Quote from: Slough
After all, when someone buys camera A, will the clouds part to reveal an elderly gentleman who goes on to say in a deep voice "Though shalt only use converter X with that camera, as should have been decreed by Moses, but he missed that one off his list due to a poor retention span and forgetting to make notes, even though I warned him 11 commandments was an awful lot to remember, what with the excitement of meeting his God for the first time, oh well, now where was I, oh yes, I must get back to that game of mah jong with Beelzebub".

Usually I steer clear of religion when discussing photography, but couldn't resist the following analogy. Actually, the Torah contains not 10 but 613 commands. I believe it was St. Paul who taught that trying to follow all 613 commands forced one to sin, since no human could possibly fulfill all of those commands. Accordingly, St. Paul and St. Peter condensed Mosiac law into simpler constructs. Some photographers are attempting to control all variables, but inevitably fail.
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wildlightphoto
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« Reply #124 on: October 16, 2009, 10:22:11 AM »
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Quote from: bjanes
As you know, raw converters usually have defaults that differ for each individual camera, and these may not be optimum for the given camera. Controlling all these variables would be a daunting task and you would still have uncontrolled variables. We are discussing aliasing, and the lens is an important factor: if the lens can't resolve above Nyquist, there will be no aliasing. What is the optimum f/stop for each lens? Do you use the same lens for all cameras? Some raw converters correct lens aberrations for their brand of camera with certain of their lenses. Sharpening is also critical, since cameras with blur filters require more sharpening than cameras lacking them. Different raw converters have different sharpening.

You've expressed exactly why a single raw converter should not be used to compare camera systems.

Quote from: bjanes
I don't know your background, and your understanding of the scientific method

degrees in biological sciences and engineering, working in engineering software development.  I understand all to well how a single software package can and will treat different data sources differently.  Using a single raw converter in no way eliminates any variables whatsoever, it's only value is the tester's convenience.

Quote from: bjanes
it might be prudent to test with a number of well regarded raw converters to determine how significant this variable is. If the results are similar or can be correlated, you might decide to settle on one raw converter. This is the approach of most testers who post results on the net. If you get the best results with the camera maker's raw converter, you still do not know if these good results are due to the camera or raw converter (which does not support any other brand of camera).

Does it matter whether the best results are from the software or from the hardware?  My impression is that the goal is optimum results, not optimum hardware by itself or optimum software by itself.  The two are inseparable, so if you are really interested in results, i.e., the photograph, find the optimum of each combination.  If the goal is optimal overall results, it doesn't matter that "most  testers who post results on the net" use a singe raw converter, it's a lazy suboptimal shortcut no matter how many people do it.
« Last Edit: October 16, 2009, 10:23:31 AM by telyt » Logged
bjanes
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« Reply #125 on: October 16, 2009, 10:30:48 AM »
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Quote from: telyt
Does it matter whether the best results are from the software or from the hardware?  My impression is that the goal is optimum results, not optimum hardware by itself or optimum software by itself.  The two are inseparable, so if you are really interested in results, i.e., the photograph, find the optimum of each combination.  If the goal is optimal overall results, it doesn't matter that "most  testers who post results on the net" use a singe raw converter, it's a lazy suboptimal shortcut no matter how many people do it.

I'm waiting to see your optimal set of tests.
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Slough
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« Reply #126 on: October 16, 2009, 10:42:18 AM »
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Quote from: bjanes
Usually I steer clear of religion when discussing photography, but couldn't resist the following analogy. Actually, the Torah contains not 10 but 613 commands. I believe it was St. Paul who taught that trying to follow all 613 commands forced one to sin, since no human could possibly fulfill all of those commands. Accordingly, St. Paul and St. Peter condensed Mosiac law into simpler constructs. Some photographers are attempting to control all variables, but inevitably fail.

   So Christianity is Judaism 'lite'? (And Church of England is for people who like coffee mornings, and songs, but aren't so fond of the religious bits.) I'd better stop there before I offend too many people ...
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ejmartin
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« Reply #127 on: October 16, 2009, 12:01:57 PM »
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telyt,  I'm curious to know how a demosaic algorithm can be tuned to do better with an image depending on whether it has been taken with or without an AA filter on the sensor.
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emil
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« Reply #128 on: October 16, 2009, 12:02:30 PM »
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Quote from: telyt
pardon my language, but speaking as a scientist that's bullshit.  The only reason to do that is if the one converter you're using is the only one you ever expect to use.  This test would be "how do cameras B and C compare when using only one converter?", not "how do Camera B and Camera C compare?"  The test with only one converter would transmogrify on the internet to "Tester A says Camera C sux" when it's really Camera C doesn't do as well as Camera B when files are converted with Converter D.  Are you only interested in Converter D?  If so then the test you propose is fine.  If you want to see how well each system performs, the test with one converter doesn't tell you the whole story.

I agree with this completely.  Many review sites make the mistake of using a "common converter" (invariably using Adobe based products for this purpose) with "identical settings" to process RAW images from different cameras from different makers, without realizing that there are differences "under the hood" in the way the "common converter" deals with these different RAW files.

Using a "common converter with identical settings" to determine how Camera A compares to Camera B is the commonest mistake that several review sites (even reputed ones) seem to be making, since using a "common converter with identical settings" will only prove how the 'common converter' handles files from Camera A and Camera B - not what Camera A or Camera B can do.  

Bottomline, the answer to how "Camera A compares to Camera B" can only be determined by choosing the optimum converter for Camera A (with settings appropriate for Camera A) and choosing the Optimum converter for Camera B (with settings appropriate for Camera  and then comparing the resulting outputs.   Obviouslly there is still the wiggle room that even the best RAW converters of today may be bettered by the ones available tomorrow and the results might be different tomorrow.


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nma
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« Reply #129 on: October 16, 2009, 01:13:17 PM »
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I have had a late start but I am trying to follow the twists and turns of this thread.

The virtues of the AA filter have been affirmed and denied, with religious certainty on both sides. One argument in favor of removing or omitting the AA filter in landscape photography is that the fine geometric patterns, such as in fabrics, are not present in the natural scene and thus aliasing is negligible.  However, sampling theory, as well as simulation, shows that this statement is false.  When an image is under sampled, components above the Nyquist frequency are erroneously used in forming the digital image, appearing as lower frequency information.  This is aliasing. Even if one doesn’t recognize it as such, it is a distortion of the image.  These distortions might be pleasing in some case and lead some to prefer a camera without an AA filter. But one cannot be certain that the camera without the AA filter will always yield the more pleasing result; it will depend strongly on the scene being photographed.  

I think it is fair to say that the digital sampling of the sensor puts a limit to the resolution that can be obtained. One should not be surprised to learn that it is impossible to get perfect fidelity in rendering digital images formed with a finite number of samples. The sampling frequency of the sensor and the MTF of the lens must be consistent or the results might not be acceptable. Some very high resolution lenses may not be well matched to every sensor design sans AA filter.

This argument could also  be turned around in favor of designs without an AA filter. By using a sensor with very high sampling, one could in principle, set the Nyquist frequency to some reasonable level, and filter out the information above Nyquist. Then the image could be downsampled as desired. In principal the sensor with high sampling could record the same total number of photons as one with lower sampling (that’s an engineering challenge for sure), so the ultimate IQ would not be worse.



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bjanes
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« Reply #130 on: October 16, 2009, 01:30:17 PM »
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Quote from: aaykay
Bottomline, the answer to how "Camera A compares to Camera B" can only be determined by choosing the optimum converter for Camera A (with settings appropriate for Camera A) and choosing the Optimum converter for Camera B (with settings appropriate for Camera  and then comparing the resulting outputs.   Obviouslly there is still the wiggle room that even the best RAW converters of today may be bettered by the ones available tomorrow and the results might be different tomorrow.

So now for a proper comparison of camera A to camera B we must test both with all known raw converters with all possible settings and then mark the results as tentative, awaiting the next generation of raw converters.

To get anywhere, I think that it will necessary to streamline the process so as to control the most important variables as determined by preliminary testing.
« Last Edit: October 16, 2009, 01:30:57 PM by bjanes » Logged
wildlightphoto
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« Reply #131 on: October 16, 2009, 01:42:52 PM »
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Quote from: bjanes
So now for a proper comparison of camera A to camera B we must test both with all known raw converters with all possible settings and then mark the results as tentative, awaiting the next generation of raw converters.

Yes.  It's always been that way, but most in the general population have too weak a grasp of the variables involved to understand how flawed the single-converter tests are.
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jing q
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« Reply #132 on: October 16, 2009, 03:23:44 PM »
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Quote from: nma
I have had a late start but I am trying to follow the twists and turns of this thread.

The virtues of the AA filter have been affirmed and denied, with religious certainty on both sides. One argument in favor of removing or omitting the AA filter in landscape photography is that the fine geometric patterns, such as in fabrics, are not present in the natural scene and thus aliasing is negligible.  However, sampling theory, as well as simulation, shows that this statement is false.  When an image is under sampled, components above the Nyquist frequency are erroneously used in forming the digital image, appearing as lower frequency information.  This is aliasing. Even if one doesn’t recognize it as such, it is a distortion of the image.  These distortions might be pleasing in some case and lead some to prefer a camera without an AA filter. But one cannot be certain that the camera without the AA filter will always yield the more pleasing result; it will depend strongly on the scene being photographed.

thank you, this could possibly sum everything up.
perhaps having no AA filter leads to "distortions", but in photography most of us never strove to capture a scene exactly as it is.
There is something to be said for the intangible sense of satisfaction one gets from seeing an image straight out of the camera looking "right" without having to post process the hell out of it.

Many people shoot not for scientific reasons, but we shoot to get images which please us, looking for the right cameras which render images the most pleasing way possible. Most people are lazy and prefer not to have to fiddle around so much with images to get them to look good.
And there is something pleasing about the way an AA filterless camera renders images.

I think the vehement disagreement regarding this topic boils down to a few things:
we have a few very scientific minded people here who regard it sacrilegious that some photographers would actually think that aliasing is acceptable and pleasing, and believe that one should strive for a theoretically perfect camera output with the best lens and raw converter possible.

there are others who simply just prefer the look of an AA filterless picture, and perhaps use scientifically inaccurate terms to describe the reason why they feel these images are better.Perhaps *shock* we don't really care for accurate photographs!

Thus the twain shall never meet. I'm happy to stay in the latter camp as long as my images look good.

I'll leave the theoretical debating to you guys  
« Last Edit: October 16, 2009, 03:25:01 PM by jing q » Logged
madmanchan
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« Reply #133 on: October 17, 2009, 10:41:05 AM »
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Even single raw converters will treat different camera models differently. For example, a given raw converter may apply different demosaic, sharpening, and NR methods to different models.
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Slough
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« Reply #134 on: October 17, 2009, 11:10:40 AM »
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Quote from: madmanchan
Even single raw converters will treat different camera models differently. For example, a given raw converter may apply different demosaic, sharpening, and NR methods to different models.

Exactly. So using one converter for all cameras is not much different from using different converters. And in any case, it seems to be, rightly or wrongly, that the difference between different RAW converters are often small as far as resolution goes. Where they differ is high ISO performance (noise), and colour rendition (which is why I use Nikon Capture despite the horrendous bugs that any self respecting software house would fix). If the differences in resolution are so small, then what size do you have to print to such that they become readily discernible to ordinary people as well as the socially challenged?

By the way, what was the question again? Or rather the point of this intellectual navel gazing?
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madmanchan
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« Reply #135 on: October 17, 2009, 03:42:34 PM »
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I think the larger point is that the whole imaging chain is complex. It is hard to isolate variables. Even when you can, it can be hard to understand how a given design point (e.g., a sensor's microlenses, or lack thereof) affect the final result. As an analogy, scientists try to attribute certain types of health benefits to specific nutrients (or types of foods) but it's very hard to understand the real effects because they are only one part of a much larger, very complex system (e.g., overall health of the individual, interaction with other foods, daily activities, etc.).
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ejmartin
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« Reply #136 on: October 17, 2009, 04:18:41 PM »
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Quote from: madmanchan
Even single raw converters will treat different camera models differently. For example, a given raw converter may apply different demosaic, sharpening, and NR methods to different models.

Yes, but there are others that don't.
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emil
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« Reply #137 on: October 17, 2009, 09:41:41 PM »
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They probably should, though, Emil. For example, I would be surprised if a demosaic method that works on a 3-channel Bayer camera works equally well on a 4-channel camera. There are also different processing requirements for Foveon, and Fuji cameras. All of these affect the initial level of quality. There's also a ton of pre-demosaic processing that needs to happen on many medium format files; otherwise the image is unusable.

In any case, the point I'm trying to make is that users conducting detailed tests are generally not able to tell (at least, not easily) whether a given raw converter treats all the models the same way ...
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JeffKohn
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« Reply #138 on: October 17, 2009, 11:32:51 PM »
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Hey Eric, when are you guys going to give us the option to disable the hidden 'basline' adjustments. ACR wouldn't get such a bad rap if it wasn't for this, IMHO. The Exposure adjustment can easily be reversed, but there's really no way to defeat the noise reduction and it hurts ACR in comparison to other converters.
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