Add DNG as a valid photo filetype

[ianrahman]

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• I have read the README and CONTRIBUTING documents
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Contributor checklist

• My commits are rebased on the latest main branch
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• [ x] My contribution is fully baked and is ready to be merged as is
• I have tested my contribution on these devices:

• iPhone 16 Pro Max, iOS 26 beta 9
• iPad Mini 2024, iPadOS 26 beta 9

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Description

Adds support for DNG as a valid image format. Resolves #4298 and #5337

Tested on two physical devices with RAW images captured on the iPhone and on a different DNG-generating camera.

[schmeat]

Nice! Current open ticket for it is #5337

[ianrahman]

@max-signal I see you self assigned the open ticket for this issue. Just wanted to point out this exists now.

[ianrahman]

@sashaweiss-signal @max-signal is there anything else I can do to help this along?

[max-signal]

@ianrahman when I investigated this last time, there were few changes we needed to make related to file sizes to resolve issues sending RAW files. The first of those was 425bf68, and there will be a few more to follow. I’ll circle back to this PR once I’ve finished the others.

[steffen-klein]

I still have this issue with DNG files on the iPhone 17 Pro for recently acquired raw photos. Older ones (maybe 1 week old) can be correctly sent as photos. But I realized that sending takes very long due to the file size. I would propose a setting to auto convert raw photos to compressed jpg before sending, this would solve all issues with raw photos. I assume most people do not want to share the raw photos anyway via signal, and if so, one could attach them as file instead of an image.

[ianrahman]

@max-signal I’m not sure you need to land those other changes prior to this PR. Aren’t the file size checks the same as those used for potentially large image types such as .tif? If you have notes from your prior investigation I’d be happy to continue to push this over the finish line.

[iceton]

Aren’t the file size checks the same as those used for potentially large image types such as .tif? If you have notes from your prior investigation I’d be happy to continue to push this over the finish line.

Any thoughts or updates @max-signal? Thanks!

[max-signal]

@max-signal I’m not sure you need to land those other changes prior to this PR. Aren’t the file size checks the same as those used for potentially large image types such as .tif? If you have notes from your prior investigation I’d be happy to continue to push this over the finish line.

Some RAW files were running into (I think, iirc) the 8 MB limit that’s imposed on certain images in certain places.