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Author Topic: Naked sensor  (Read 11464 times)
welder
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« Reply #20 on: February 17, 2012, 10:29:02 AM »
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I believe this is a matter of normal inquisitiveness. When we view the real world, we expect to see greater detail the closer we look at any object. If our eyesight is not up to the task, we know that we will be able to see more and more detail as the power of the magnifying glass increases.

The photograph has the reputation of 'capturing' reality, albeit in a 2-dimensional format most of the time. However, if one approaches a large print to view the fine detail and instead discovers bluriness, it's a disappointment.
For me personally, it is even more disappointing to examine a large print up close and discover jagged edges from aliasing artifacts.
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Isaac
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« Reply #21 on: February 17, 2012, 10:29:39 AM »
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I am a cynic. I expect companies to introduce those products that (according to their predictions) cost the least to manufacture, that can sell i the biggest numbers and at the highest selling price.
That isn't cynicism it's basic economics.
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theguywitha645d
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« Reply #22 on: February 17, 2012, 11:00:07 AM »
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The photograph has the reputation of 'capturing' reality, albeit in a 2-dimensional format most of the time. However, if one approaches a large print to view the fine detail and instead discovers bluriness, it's a disappointment. Have you never experienced that before, theguywitha645d?  Grin

Yes, but that is usually a result of bad technique, not specifications of the media. (And I have never thought to myself that it comes down to an AA filter.)

But I have never known anyone to expect an image not to change with viewing distance. It is a pleasant surprise when the detail is robust, but neither is it unexpected that an image does not have endless detail. And here again I would argue that the AA filter is not the determining factor.

I certainly pixel peep--it is fun and it provides some useful information. The question is what kind of information and the significance of that. I have been told that I should not stop down past f/11 with my 645D because the effects of diffraction can be seen. So one of the first things I did was to shoot a test at f/22 and make a 3 foot print. The idea that diffraction is really a function of format size rather than pixel pitch still holds true (someone ever suggested to me that blurring by diffraction at small apertures would simply offset the additional DoF, which of course is not true).

Now, every photographer is going to define acceptable image quality in their own way. Reid certainly has. My point is that an extreme view that every bit of resolution that you can wring out of your system is important is not really a very useful position nor really taking into account all the factors in image making/formation and the perception of that image. I am pretty sure that you know how to round and work with significant figures in math, I think photographers simply need to understand the equivalent process in imaging. OCD is a psychological condition, not a photographic technique.
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Rob C
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« Reply #23 on: February 17, 2012, 12:25:50 PM »
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You can imagine my disappointment when I actually read the first post! Such an inviting title, I though, news of a promising bit of new technology - but I guess I should have known about books and their covers; I'm wondering if there are grounds for misrepresentation...

; -)

Rob C
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BJL
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« Reply #24 on: February 17, 2012, 12:43:51 PM »
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Ray,

    Two comments:

1) Any discussion of the pros and cons of AA filtering that never mentions the raison d'être of the OLPFm namely the demonstrated image degradation due to aliasing (including but not limited to moiré) is rather pointless. It is like so many of the endless gear-head debates where some people declare that one single measure of virtue is of paramount importance and should always be maximized, ignoring sacrifices made in order to increase that one virtue. A famous example: arguing for the superiority of one sensor in given format size over another solely on the basis of higher resolution despite worse noise did not work out well for the Kodak 14N vs the Canon 1Ds.

Edit: another example: there is a very easy way to get improved resolution at equal or better equal ISO speed, and even to do it with no risk of moiré: switch from color to monochrome. The moral, as with the OLPF, is that getting the color right can be important too! Maybe the market for unfiltered sensors will be comparable to that for the monochrome sensors that are repeatedly called for.


2) The filmic equivalent of 100% viewing is examining the negative/transparency under a microscope, enlarged enough to see the individual grains or dye clouds. Both are extreme magnification, beyond what viewers will see at any same print size/viewing combination, and though both might possibly have some technical value in comparisons where all other relevant factors are roughly equal, say when comparing two lenses on the same camera, they are mostly rather remote from any worthwhile judgement of image quality as will be perceived in end usage.
« Last Edit: February 17, 2012, 12:49:04 PM by BJL » Logged
Ray
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« Reply #25 on: February 17, 2012, 11:50:06 PM »
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Any discussion of the pros and cons of AA filtering that never mentions the raison d'être of the OLPFm namely the demonstrated image degradation due to aliasing (including but not limited to moiré) is rather pointless.

BJL,
Any discussion of the pros and cons of AA filtering would have to mention the cons of image degradation, otherwise it wouldn't be a discussion of pros and cons. (Although, in the case of the D800E the cons could relate to non-image factors such as price.)  Grin

However, my post wasn't specifically about the pros and cons of an AA filter but the significance of small improvements in some aspect of technical performance, such as resolution, which may be given undue attention by people who only judge image quality at 100% size on their monitor, a size which is usually representative of a much, much larger print than such people may ever produce from their images.

For example, if one compares 100% crops of D800 and D800E images on an average 24" monitor with HD resolution of 1920x1080 pixels, and one sees a minor degree of extra crispness in the D800E image, one should be aware that such differences would only be apparent (hopefully) on a print from the same crop that one sees on the monitor, and at least the same size as the crop one sees on the monitor. If one were to make a print of the entire uncropped image it would be approximately 7ft wide and 4ft 7" high, and to see the same differences one noticed on the monitor at 100% one would need to view the 7ft wide print from the same distance one views a monitor.

(I think my maths is correct here. I'm working on the basis that the D800 image after conversion is about 109Mb in 8 bit mode, that a 24" monitor is about 20-21" wide, and that the resolution of such a monitor, if it's HD, is about 90 ppi.)

So far, the differences I've seen in the few comparison crops that are available, in respect of the D800 and D800E (refer Erik's example in reply #15), are not a cause for excitement, especially when one considers the disadvantages of more frequent and more severe aliasing artifacts.

I can understand a manufacturer of expensive MFDBs omitting the AA filters to keep costs down. The customer can then be positive about the slight advantage of a lack of AA filter, as MFDB owners generally are, and downplay the disadvantages of moire. But it doesn't make the same sense for a manufacturer to charge extra for the privilege of not having an AA filter when the advantages are so slight and the disadvantages sometimes significant.

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ErikKaffehr
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« Reply #26 on: February 18, 2012, 01:25:37 AM »
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Hi,

I actually think it is OK to pixel peep at 1:1. Those are the pixels that actually go into the image.

On the other hand, it is seldom intended that we look at an image at actual pixels, unless we have a 60" wide screen at 100PPI. That would be nice, by the way.

So we discuss prints. When we print the image, consisting of all the pixels we see at 1:1, is converted by a smart rescaling algorithm to either 360 PPI, 720 PPI or what happens to your native resolution. In the next step output sharpening will be applied. The image driver will translate the RGB pixels to a CMYK dithered pattern that will be sprayed on the ink receiving layer of the paper. Finally the ink droplets may diffuse and dry. So the actual pixels image is going trough a lot of processing before it ends up on paper.

Another factor is that human vision is very sensitive to contrast, essentially, a contrasty image is perceived more sharp. That is a very good reason to include a color checker in all tests. If we assert that grey fields match between compared samples the probability that tonal differences would affect our comparison is greatly reduced.

Regarding the D800/D800E we will see. I guess that it takes careful work to take those systems to the limit, although we have been at the same limit with 16MP APS-C for a relatively long time.

Best regards
Erik






I think Reid is making a fundamental error in his evaluation. He is evaluating images at 100% on a monitor view. That is not a real world conditions. And as the pixel count goes up, that condition moves further and further away from a real viewing condition. The variability in the photographic process going to be far more significant than an AA filter--having an AA filter does not result in a soft image, just some loss to frequencies at the Nyquist limit. Reid's own argument suggests he really does not know, he is simply making an argument that because he thinks he sees detail at 100% more clearly without an AA filter, that that is significant detail. I have never read that is true nor do I have experience that that is true--my experience fits the theories I have studied. Reid himself does not really offer any support to his claim.
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ErikKaffehr
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« Reply #27 on: February 18, 2012, 01:53:44 AM »
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Hi,

Although color moiré is the most obvious artifact, there also is monochrome moiré and that cannot be filtered out.

The issue I see is that an unfiltered sensor creates fake detail. All detail right of the red line in the enclosed image is fake. It may show up and enhance impression of sharpness, like fake goosebumps on skin, fake details in feathers.

The enclosed image was made with an OLP-filtered camera that has a weak filter. The experiment was set up to investigate/demonstrate aliasing. The reason I made it was because I have seen a lot of issues in my images that looked as aliasing to me.


Best regards
Erik




Edit: another example: there is a very easy way to get improved resolution at equal or better equal ISO speed, and even to do it with no risk of moiré: switch from color to monochrome. The moral, as with the OLPF, is that getting the color right can be important too! Maybe the market for unfiltered sensors will be comparable to that for the monochrome sensors that are repeatedly called for.



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Ray
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« Reply #28 on: February 18, 2012, 02:10:36 AM »
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So we discuss prints. When we print the image, consisting of all the pixels we see at 1:1, is converted by a smart rescaling algorithm to either 360 PPI, 720 PPI or what happens to your native resolution. In the next step output sharpening will be applied. The image driver will translate the RGB pixels to a CMYK dithered pattern that will be sprayed on the ink receiving layer of the paper. Finally the ink droplets may diffuse and dry. So the actual pixels image is going trough a lot of processing before it ends up on paper.


Erik,
I'm assuming that what one sees on the monitor can be faithfully rendered on a print of the same size as the crop on the monitor, with the right technique. At least that's what I would consider the goal of a good printing technique. One doesn't expect to see colors and detail on a print which are invisible at 100% on the monitor. Likewise, it would be frustrating if the print could not deliver the detail one sees on the monitor, when the size of the print is large enough to accommodate the detail.

Of course, there are always distinguishing differences between a reflective medium and a transmissive medium, but I'm sure you know what I mean. If one can discern the tiny eye of an insect on a leaf in the middle of a large composition, at 100% on the monitor, one expects to be able to see that eye on a print of a crop of that portion of the image.

Whether or not the lack or presence of an AA filter would make the difference between being able to discern that eye or not, is the sort of thing that needs to be determined. Grin
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ErikKaffehr
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« Reply #29 on: February 18, 2012, 03:03:06 AM »
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Hi,

Actually I don't think it is possible, because they are very different devices. A monitor used to have around 100 PPI and a printer uses something like 360 PPI res implemented as a 1440 or 2280 DPI dither pattern. The screen is continuous tone while inkjet has only few tones. So there will be a lot of transforms on the way, and it will take quite a lot of dots in the print to represent a simple pixel.

Best regards
Erik




Erik,
I'm assuming that what one sees on the monitor can be faithfully rendered on a print of the same size as the crop on the monitor, with the right technique. At least that's what I would consider the goal of a good printing technique. One doesn't expect to see colors and detail on a print which are invisible at 100% on the monitor. Likewise, it would be frustrating if the print could not deliver the detail one sees on the monitor, when the size of the print is large enough to accommodate the detail.

Of course, there are always distinguishing differences between a reflective medium and a transmissive medium, but I'm sure you know what I mean. If one can discern the tiny eye of an insect on a leaf in the middle of a large composition, at 100% on the monitor, one expects to be able to see that eye on a print of a crop of that portion of the image.

Whether or not the lack or presence of an AA filter would make the difference between being able to discern that eye or not, is the sort of thing that needs to be determined. Grin
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Ray
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« Reply #30 on: February 18, 2012, 07:35:08 AM »
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Hi,

Actually I don't think it is possible, because they are very different devices. A monitor used to have around 100 PPI and a printer uses something like 360 PPI res implemented as a 1440 or 2280 DPI dither pattern. The screen is continuous tone while inkjet has only few tones. So there will be a lot of transforms on the way, and it will take quite a lot of dots in the print to represent a simple pixel.

Best regards
Erik


Sorry! I can't follow this, Erik. Are you saying that in your experience you actually lose detail that you see on the monitor, when you make a print? This is not my experience.

In my example of a 109MB D800 image viewed at the pixel level on a 24" HD monitor, the full image that's viewed would be 7ft wide (or 2.1 metres) at the monitor's resolution of 90 or 91 ppi.

If one were to print such an image at that size, of course one would first upres it to at least 240 ppi, if not 300 ppi, and apply an appropriate amount of sharpening for that output size. Generally, large prints need to be more contrasty, so one would probably apply some additional 'local contrast' enhancement.

The resulting file size would be about 770MB at 240ppi and over 1GB at 300ppi. What's the problem?

Cheers!
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ErikKaffehr
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« Reply #31 on: February 18, 2012, 07:51:34 AM »
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Hi,

No, I didn't say anything like that. What I said is that is not possible to exactly reproduce a crop on screen on print media.

Best regards
Erik


Sorry! I can't follow this, Erik. Are you saying that in your experience you actually lose detail that you see on the monitor, when you make a print? This is not my experience.

In my example of a 109MB D800 image viewed at the pixel level on a 24" HD monitor, the full image that's viewed would be 7ft wide (or 2.1 metres) at the monitor's resolution of 90 or 91 ppi.

If one were to print such an image at that size, of course one would first upres it to at least 240 ppi, if not 300 ppi, and apply an appropriate amount of sharpening for that output size. Generally, large prints need to be more contrasty, so one would probably apply some additional 'local contrast' enhancement.

The resulting file size would be about 770MB at 240ppi and over 1GB at 300ppi. What's the problem?

Cheers!
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BJL
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« Reply #32 on: February 18, 2012, 09:44:51 AM »
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Ray and Erik,

I am mostly on Ray's side on the low value of 100% pixel on-screen viewing. I never felt the need to view my negatives enlarged enough to see the individual light detecting elements (silver grains, the pixels of traditional monochrome film), and see little or no need to do so in order to evaluate the image quality that can be got from a digital file. It is, as some one else said, the difference been "measurable" and "significant". This is well-known to working scientists and probably even more so to successful engineers and product designers, but is often missed by us dilettantes, who are these days faced with a flood of easily acquired data but sometime have a deficit of ability and judgement to draw practical conclusions from the data.

On the other hand, I agree that it is unclear how to use on-screen viewing as a completely reliable surrogate for print image quality: color gamuts and dynamic range differences also complicate things.
« Last Edit: February 18, 2012, 05:41:27 PM by BJL » Logged
hjulenissen
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« Reply #33 on: February 18, 2012, 05:26:05 PM »
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That isn't cynicism it's basic economics.
What is the difference? :-)

-h
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opgr
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« Reply #34 on: February 18, 2012, 05:49:17 PM »
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Hi,

Although color moiré is the most obvious artifact, there also is monochrome moiré and that cannot be filtered out.

The issue I see is that an unfiltered sensor creates fake detail. All detail right of the red line in the enclosed image is fake. It may show up and enhance impression of sharpness, like fake goosebumps on skin, fake details in feathers.

The enclosed image was made with an OLP-filtered camera that has a weak filter. The experiment was set up to investigate/demonstrate aliasing. The reason I made it was because I have seen a lot of issues in my images that looked as aliasing to me.


Best regards
Erik


This has nothing to do with unfiltered sensors. This looks more like a really really bad RAW converter, which might explain why you have seen a lot of issues. Which RAW converter did you use?
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Oscar Rysdyk
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« Reply #35 on: February 18, 2012, 06:01:03 PM »
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Sorry Erik,
I didn't make myself clear: I meant switching to a monochrome sensor with the same cell size, or from color to monochrome film. Both can increase resolution, but at an often unacceptable price. My point was only a soemwhat extreme example of why we should not fetishize resolution alone when evaluating image quality.
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nma
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« Reply #36 on: February 18, 2012, 08:42:54 PM »
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This question,  to AA or not, has been raging for a very long time. Photographers who are experts in evaluating images often argue that the camera without the AA filter makes superior images. I stipulate that these experts really know what they are looking, with respect to the popular and fine-art appeal of images. This AA argument is reminiscent of the “golden ears” of the high-fidelity audio era, who claimed that amplifiers with tubes sounded better than transistor amps and that CD's did not sound as good as analog recordings on vinyl.

Some “experts” say things like the per pixel sharpness of the AA-less sensor is superior. There are many statements like that, offered with religious certainty but no scientific basis. How, for example, can a term like per pixel sharpness have any meaning when it takes more than one digital sample to represent a line-width? Put another way, the line intensity has a characteristic width in any imaging system and it takes at least two digital samples to represent that variation.  If you had higher digital sampling the image fidelity should improve, but these experts would see that as lower per pixel sharpness. 

The question is are experts like Reid, Reichman and others religiously sure, or do they really understand the mathematics and engineering of digital imaging? Are we sure that the differences they see are due solely to the lack of an AA filter? Are we sure that the images without AA filters exhibit higher spatial resolution? We know there are some distortions in the images with AA-less sensors. Of course the AA-filtered images are not perfect either. They have different distortions, due to the imperfect roll-off of the AA filter and the properties of real lenses.

Understanding the formation and sampling of the Bayer-array sensor is very complicated. The reason it is so complicated is that the blue and red elements have different sampling (lower Nyquist frequency) than the green elements. If the RGB elements were considered independently and the resolution was set by the blue and red, it would be easier to analyze. But in order to wring the last drop of image quality out of the Bayer array, the Nyquist sampling theory is replaced with more aggressive algorithms that exploit the spatial correlations in the images. But as a general rule, I would say that when you push a system like that and remove the AA filter, you are asking for trouble. There will be situations where removing the AA filter will have higher apparent sharpness. But I argue that this appearance is due to aliasing.  Those “experts” who think that aliasing only occurs when there are repetitive structures in the image are wrong. On the contrary, whenever there is high frequency information above Nyquist from the lens which is not removed BEFORE image formation, it will be incorrectly rendered at lower frequency. Maybe we will like the appearance of a little aliasing, just like many liked the distortions of tube amplifiers and vinyl records.  But before we drive the field down what may very well be the wrong road, the science and engineering should be clarified. We should not be ruled by those with the biggest megaphone who are arguing on the basis of experience and intuition.
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ErikKaffehr
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« Reply #37 on: February 18, 2012, 10:42:21 PM »
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Hi,

I used Lightroom 3.6. I forgot to mention that the screen dump was made at 2:1 (twice actual pixels). The attached samples are shot at f/5.6 and f/16.

The test pattern is Norman Korens MTF test target: http://www.normankoren.com/Tutorials/MTF5.html#using

Best regards
Erik



This has nothing to do with unfiltered sensors. This looks more like a really really bad RAW converter, which might explain why you have seen a lot of issues. Which RAW converter did you use?

« Last Edit: February 18, 2012, 10:51:49 PM by ErikKaffehr » Logged

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« Reply #38 on: February 18, 2012, 11:13:00 PM »
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Hi,

I used Lightroom 3.6. I forgot to mention that the screen dump was made at 2:1 (twice actual pixels). The attached samples are shot at f/5.6 and f/16.

The test pattern is Norman Korens MTF test target: http://www.normankoren.com/Tutorials/MTF5.html#using

Best regards
Erik


From the original ACR plugin to the current LR I don't recall ever seeing the errors you show in these samples. The colorized edge errors are characteristic of a RAW converter with inadequate edge detection, such as for example Canon's DPP, Iridient Raw developer, Silkypix, to name just a few i tested recently.

Would you have the original RAW file available for us?
 
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« Reply #39 on: February 18, 2012, 11:53:31 PM »
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Hi,

http://echophoto.dnsalias.net/ekr/images/Articles/Aliasing/_DSC0963.ARW

Best regards
Erik


From the original ACR plugin to the current LR I don't recall ever seeing the errors you show in these samples. The colorized edge errors are characteristic of a RAW converter with inadequate edge detection, such as for example Canon's DPP, Iridient Raw developer, Silkypix, to name just a few i tested recently.

Would you have the original RAW file available for us?
 

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