1. As usual when new Leica cameras come out, I took a quick look inside a DNG from one of Leica's new Leica CL  cameras:

    1. The camera name shows as "LEICA CL"
    2. The image data is 14-bit. There is no compression used in the DNG I looked at. 
    3. The DNG version is 1.4, with a "backward version" of 1.3. There is a reason for this - DNG 1.3 allows for opcodes, which Leica use for lens correction.
    4. In the DNG I looked at, which was shot with a "Summicron TL 1:2 23 ASPH." lens, lens correction is done by a single "WarpRectilinear" operation in the DNG. 
    5. In addition to the lens correction op code, there is also a "FixBadPixelsConstant" opcode, whose function is exactly as the name states. This is the same as in the Leica Q, SL, etc.
    6. Unusually, the DNGs all contain 2 different JPEG preview images in addition to the main raw image, one of 1620x1080, and finally a full sized preview of 6000x4000. Having the full sized preview is particularly odd, as it takes up a lot of space. In the approximately 45 MB files I've seen, the full size preview typically takes up about 1.8 MB. 
    So in summary, the DNGs appear to be a bit of a hybrid of the "SL", "Q", etc style of DNG, with a single lens correction opcode, and a bad pixels correction opcode, and of the "M10" style of DNG, with a full sized preview. As I noted in my analysis of the M10 DNG, the full size preview is probably there to support viewing on mobile devices that often don't have raw decoding capability built in. 

    Finally, it's notable that the DNGs don't contain the bizarre Lightroom XMP metadata that the M10 DNGs have embedded in them. 
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  2. So finally, after many years of searching, I have an answer to the question that torments all who go down the digital color rabbit hole.

    This is from XKCD, brought to my attention via an article on the Digital Transitions website about the Phase One IQ3 100mp Trichromatic.



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  3. Back in January, when the new Leica M10 was introduced, there were claims that the improvement in dynamic range from the Leica M240 to the M10 was of the order of 1.5 to 2 stops.  At the time, I wrote that just by eyeballing the published images, I believed the improvement to be "closer to 0.5 stops than 1.5-2".

    Much to my surprise, given what I had thought to be just a basic explanation of why dynamic range is a tricky concept, the post generated a lot of push-back. And I mean a LOT.

    Well, now there is actually an independent third-party measurement available, from photonstophotos.net:


    And....(drum roll)....the improvement in DR between the M240 and the M10 is 0.55 stops. As I predicted back in January.

    You can a find whole lot more information, including a useful interactive graphing tool that allows you to compare cameras, on the photonstophotos.net site.
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  4. dcpTool has been available for quite a while as a command line application for Windows and the Mac. But now it available in the form of an easy to use Mac app, with powerful batch processing capabilities. dcpTool for the Mac is available from the App Store.

    dcpTool allows you to:

    1. Decompile DNG Camera Profile (DCP) files in XML. The XML can then be read and edited with a simple text editor.
    2. Recompile edited XML into DCP files
    3. Remove "Hue twists" from camera profiles. 
    For more information on hue twists, see these posts:
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  5. Many cameras embed lens corrections into raw the raw files that they produce. Generally, that's a good thing - straight lines stay straight, etc. For an example of lens corrections in practice, take a look at this post about the Leica SL.

    But, as the saying goes, "there is no free lunch". Lens corrections also have some downsides:

    • Lens corrections result in a small reduction in sharpness. Sean Reid, at Reid Reviews has done extensive testing on this as part of his various lens reviews, and his conclusions are clear - there is a measurable loss in sharpness.
    • Lens corrections result in some reduction in image size - the corrections inevitably result in the edges of the image curving, and the curved parts need to be trimmed off to get back to a straight edge.
    So sometimes, it's useful to be able to get an uncorrected image. Now there are some raw developer apps that allow you get to uncorrected images (AccuRaw EXR is one of them), but most mainstream apps such as Lightroom and Photoshop don't allow correction to be disabled.

    Fortunately though, there is a "simple trick" that will allow you to disable lens corrections for nearly any camera that produces raw images. What you need to do is a simple two step process:
    1. Firstly, convert the raw image to a DNG image, using Adobe's DNG converter.
    2. Then use DNG Cleaner (macOS only) to remove any opcodes.
    The resulting DNG will not have any lens correction, and you can load it into Lightroom, Photoshop, or any other app that supports DNGs.

    Why does this work? This works because whenever DNG Converter converts an image that needs lens correction, it embeds the required correction as an "opcode" into the DNG image. Lens correction opcodes as usually things like "WarpRectilinear". DNG Cleaner knows where to find these opcodes, and simply removes them, as long as you have the "Remove opcodes" checkbox selected:


    Note that in order for this to work, you need DNG converter to be using it's default settings. Specifically, Compatibility should be set to the most recent version of Camera Raw. You should definitely not be using Custom Settings with the "Linear" checkbox selected. "Linear", otherwise known as LinearRaw, bakes any corrections into the actual data in the DNG, making it impossible to remove.

    There's more information on the DNG Cleaner website.
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  6. Those of you that have read the Leica M10 raw file analysis post will know that M10 DNGs have more baggage in them that is typically the case for a Leica DNG. I've put together a little app to clean them up, called DNG Cleaner (Mac only for the moment). For M10 DNGs this will remove:

    1. The full size image preview - that will save about 3MB
    2. The various Lightroom/Photoshop adjustments embedded in the XMP portion of the DNG - ISO dependent noise reduction settings, lens profiles, etc

    DNG cleaner will also optionally remove opcodes, and apply lossless compression. This isn't relevant to the M10, but in many other Leica cameras, e.g., the Q, the SL, etc, opcodes are used for lens correction. For an example of the SL's with and without lens correction, see my post on the subject. DNG Cleaner is what Sean Reid used to remove opcodes for his SL 50 review, which some of you will have seen.

    As ever, back up your files before using any app that is designed to modify them.

    For more information on DNG Cleaner, see the website.
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  7. AccuRaw users might have gotten a bit of a surprise recently - AccuRaw has turned into AccuRaw EXR, and is now at version 3.

    The reason for the name change is that the focus of the AccuRaw product has changed a bit, based on what users were actually doing with it. AccuRaw has always been focussed on having highly linear color response, with no "hue twists" or other surprises in the color rendering. As it turns out, that is a very useful feature to have if you're composting stills into video - it reduces the amount of work required for color matching.

    In the world of video, especially in the professional cinematography world, the "gold standard" is to use a format such as EXR, which is a floating point format. That allows huge flexibility in the way that post processing is done. So the new version of AccuRaw, now named AccuRaw EXR, supports EXR output.

    However, it's more than just a name change. In order to really support EXR output, AccuRaw has seen major changes internally - it now has a fully floating point, non-clipping workflow. For more on why that is important, see this post.

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  8. Good news - AccuRaw, AccuRaw Monochrome and PhotoRaw now have support for the compressed raw format that Fuji use in the new GFX 50S. Previous versions of AccuRaw/PhotoRaw had support for the regular uncompressed RAFs, but not the compressed version. That's now resolved, and any GFX 50S file should now work. This is thanks to Alexey Danilchenko and the folks over at LibRaw, who added support for Bayer compression to their previous X-Trans compression work.
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  9. Updated: AccuRaw and PhotoRaw now have support for compressed and uncompressed RAFs.

    For those that have been asking me about AccuRaw and Fuji GFX 50S support, I'm pleased to say that the version on the App Store as of today has support, although only for uncompressed RAFs. Compressed support will follow over the next few weeks. But now you can take a close look at GFX raw files using AccuRaw.

    Of course, the new support also applies to both AccuRaw Monochrome, and PhotoRaw. At the same time, the new version also adds support for other new cameras, including the Fuji X100F, the Fuji X-T20, the Nikon D5600, and the Leica M10
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  10. I've been reading various articles, posts, etc on the web that deal with Leica's new M10. Many of those suggest that the improvement in dynamic range from the Leica M240 to the M10 is of the order of 1.5 to 2 stops. But I find that difficult to agree with.

    I would guess the improvement in dynamic range between the M10 and the M240, just by eyeballing the published images, to be closer to 0.5 stops than 1.5-2.

    Which raises an interesting question - why the huge discrepancy, when everybody is looking at the same images?

    What is Dynamic Range?

    To someone like me, with seven years of engineering school, the definition of dynamic range is deceptively simple - for an image it's (in non-mathematical terms) the difference between the lightest and darkest levels in which detail is discernible. Usually, dynamic range is measured in stops, or EVs.

    So the problem is???????????

    Actually, there are two problems. Firstly, there's a major problem of definition, and then there's a minor problem of measurement.

    For simplicity, I'll deal with the minor problem first:

    The minor problem of measurement

    The minor problem of measurement is a fairly simple one - what exactly does "detail is discernible" actually mean?

    By way of example, does that mean you could recognize a black cat against a black background? Or a white cat against a black background? Well, as it happens, there is a standard, although (regrettably) it has nothing to do with cats, black or white. For engineers, the most commonly used definition is that "detail is discernible" means that the signal to noise ratio is one. Now you should note that a cat at a signal to noise ratio of one doesn't actually look much like a cat. Or anything. From the folks at Point Grey:

    Now there are a whole host of additional complications - for example:
    • Color images have red, green and blue channels that saturate at different levels - so does detail vanish when one channel is saturated, or all channels?
    • Images in cameras are digitized, and digitization creates it own noise. Are you including that or not? Also, are you including amplifier noise, etc?
    • Human perceptions of signal to noise ratios aren't too good. Notably, you can use dithering (basically, adding carefully controlled amounts of noise) to make a picture look better. Technically, this increases the perceived signal to noise ratio. So sometimes, when you see a signal to noise ratio quoted, it's "perceptual".
    On the last point about dithering, one of the reasons, although not the most important, why I called Adobe's lossy DNG compression an "engineering abomination" a few years ago was that it clips images to 8 bits, and then uses dithering to make the images look better. 

    So there are good reasons why you could have different people measure the dynamic range of a camera, and they could come to somewhat different answers. By way of example, I'll contrast two different sources of dynamic range measurements for cameras: 
    • DxOMark. DxOMark is well known in the photographic community - basically, loved and hated by equal measure. I have my issues with what DxOMark does - mainly that they're not very transparent about how they get to their measurements, and some measurements don't make a whole lot of sense. But they do apply a consistent set of measurements that at least provide a common basis for comparison that you won't get from the camera manufacturers. Or most camera sites either.
    • Sensorgen.info. Sensorgen.info is the imaging nerd's site - it has information that people that work with image sensors want to see, such as quantum efficiency and saturation capacity.
    Here's a table of what both sites say about the dynamic range of some cameras:


    Firstly, you'll note that DxOMark is consistently 0.6 to 1 stops higher than Sensorgen. Next, those with a technical background will notice something odd - the DxOMark result for the D810 is 14.8. But, for a camera with a 14-bit A/D such as the D810, that's impossible, at least if you're using the standard definition of dynamic range, because the maximum dynamic range achievable would be 14. My guess is that one reason for the difference between the two sites is probably that DxOMark is trying to remove the effects of A/D resolution, and just look at the sensor as an analog device. They may also be trying to compensate for the presence of other sources of noise, e.g., in the amplifiers. That would remove the quantization noise element, and give a consistently higher reading for dynamic range across the board. But if anyone knows exactly how DxOMark do their measurements, I'd like to hear from them. 

    But what is reasonably consistent is the difference between cameras. So, e.g., DxOMark view the M240 as 1.6 stops better than an M9 versus Sensorgen at 1.4 stops. For what it's worth, my experience from when I've had the opportunity to test cameras in an optics lab is that Sensorgen is closer to the readings that I get. Of course, I'm measuring the whole package, not trying to isolate just the sensor.

    So, bottom line - there are legitimate technical reasons why not everyone will agree about exactly what the dynamic range of a given camera is. But those differences tend to be more about what the absolute number is, rather than the relative performance of cameras. So while DxOMark and Sensorgen disagree about whether the dynamic range of an M240 is 12.5 or 13.3, they both agree that it's dynamic range is at least a full stop better than the M9, and at least half a stop worse than a Sony A7R.

    The Big Problem of Definition 

    But the differences in measurement don't explain why my guess of the M10's dynamic range relative to the M240 was so far from many individuals with a great deal of experience of Leica's M cameras. Some additional research led me to believe that many of those individuals were concluding that the M10 was usable at 1.5-2 stops higher ISO than the M240. "Usable" here being defined as being able to produce a print that was commercial usable without extensive post-processing. Based in large part on the 1.5-2 stops higher usable ISO, they were then concluding that the M10 had 1.5-2 stops of additional dynamic range. Unfortunately, that's not a conclusion that you can safely draw.

    The reason why an increase in usable ISO doesn't necessarily imply the same increase in dynamic range goes back to the definition of how dynamic range is measured, which is based on whether detail is discernible within noise. But how "usable" an image is in the view of a photographer takes a lot more than just noise into account - it's an assessment of the entirety of image quality. In the specific case of the M240 vs. the M10 the culprit is probably banding. Now banding does contribute to noise, but perhaps less than many might think. Banding is usually lighter and darker bands across the image, usually numbers of pixels wide.  But within those bands, detail is still discernible. It's actually only on the transition between bands, the edges, that banding makes discerning detail more difficult, and contributes to noise. So the effect of banding on a noise measurement, and hence on dynamic range, is less than you might guess. But banding, even light banding, can quickly make an image unusable.

    This then is the problem of definition - there's a general assumption that improvements in dynamic range and improvements in high ISO performance are effectively the same thing. That's not the case - for a "perfectly designed camera", a camera where the only source of image quality imperfection was simple sensor noise, that would be true. But in real cameras, quite frequently there are other sources of defects in image quality. As soon as those other sources come into play, then the direct equivalence between dynamic range and improved high ISO performance is no longer valid.

    Conclusion

    So, in summary, here's the explanation:  It's probably quite reasonable to say the the M10 has a 1.5-2 stop advantage over the M240 at higher ISO. But that doesn't mean that the M10's dynamic range is 1.5-2 stops better than the M240, simply because the M240's practical usability to a photographer is mostly limited at higher ISO by banding, not by simple noise performance.

    So what should you take from all this? Given the issues with dynamic range as applied to cameras above, my best recommendation is that, unless you are actually in an optics lab, just avoiding mentioning the phrase "dynamic range" is probably the best way to go.

    Note: this post has been updated since it was first published.

    Also Note: There's an update here, with the actual measured M10 dynamic range.
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