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I am currently re-designing by photo-workflow and my plan so far is to convert the RAW-files from my Sony camera (which produces Sony's RAW, ARW) to DNG-format (which is Adobe's RAW). I use Adobe's "Digital Negative Converter" tool for that.

I am now testing my new workflow, using Darktable as the tool to generate the JPGs out from the RAWs. While testing, I found one distinction between the original RAW-files from my Sony and the DNG-files which surprised me a lot and keeps confusing me - I couldn't find a proper explanation for it.

--> It seems that all my pictures I generate from the converted DNG-files are slightly cropped. Just slightly, but visible. To test and verify that, I exported JPGs from the different RAW formats with darktable. I did not apply any modules to them (so not cropping, changing parameters etc, just exporting JPGs from the RAW data). The JPGs from DNG are slightly cropped.

From what I read, the original RAW-data should be untouched by the conversion tool. It's just the format of the file itself, storage of metadata etc which changes.

Testfiles:
https://web.fp.ong.at/FPS08962.ARW
https://web.fp.ong.at/FPS08962.DNG

Disclaimer: I am fully aware that the embedded preview-JPG is no benchmark for evaluating the content of the file. I did proper exports from RAW to JPG, and compared those, to evaluate this effect.
This question is not whether it is a good idea or not to convert to DNG. I want to do it because Sony does not offer lossless compression of their RAW files. I am aware of arguments against it (there were already a few questions/discussions here about that).

  • When viewing both images in the standard Mac Preview Window, the ARW file cuts off the right edge of the sign(Feuerwehr) and seems slightly copped compared to the DNG file which shows full sign and also some stonework after the sign. When imported in Lightroom, they both show the same as the ARW file, with the extra detail of the .DNG file missing. When exported to jpegs from Lightroom, they are both showing as identical, but still with the extra detail of the .DNG missing. – Abdul Quraishi Mar 11 at 15:24
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    What I am seeing to what you are describing, doesn't make sense. specially what I am witnessing! if anything, it is possible that DarkTable is utilising the full sensor pixels including the border pixels which generally are supposed to be cropped. whereas the DNG is by default copping the edges as its supposed to. Thats the only explanation I can think of. – Abdul Quraishi Mar 11 at 15:41
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I took a look at your raw files. It seems there is extra data from the Sony sensor that is present in the ARW and DNG files but which is not designed to be part of the standard image size (6000x4000 in your case). This is likely the extra pixels around the edge of the sensor that help make in-body image stabilization work in your particular Sony camera.

I can see the effect you describe in Mac OS "Preview", which shows the extra pixels in the DNG image but not the ARW image (for me, anyway). However, when both DNG and ARW are loaded into Adobe Camera Raw, ACR crops the image to 6000x4000 per the metadata in the RAW file. So both DNG and sony ARW look the same in Lightroom and Photoshop -- 6000x4000 pixel images.

When I load both ARW and DNG into Darktable, it shows the image dimensions as 6048x4024. So the extra pixels appear to be an artifact of Darktable. It's processing the images differently and showing you the additional pixels.

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    Thank you for your investigation! I will do further research if darktable for some reason does not crop areas of the raw-file which actually should be cropped. Perhaps implementation of meta-data of ARW-files is not complete (while for DNG it is). I will also compare it with the out-of-camera JPGs. If I find something interesting, I will post it here. – sephiroth Mar 13 at 21:47
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There's an Adobe help article about a similar issue, although it refers to old versions of LR and ACR, and other cameras: Images cropped unexpectedly in Lightroom.

In this, they recommend the use of the Adobe DNG Recover Edge plug-in. You can try if this will reveal the missing edge pixels in your DNG's.

I'm aware you're using Darktable, but you can try with a trial version of Lightroom. There used to be a standalone DNG Recover Edges tool (https://luminous-landscape.com/dng-recover-edges/) but the d/l link is dead. I found it on the waybackmachine: https://web.archive.org/web/20071215115308/http://www.luminous-landscape.com:80/recover_edges/ but no guarantees whether it will still work with current DNG versions...

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