Problem with preview generation on "ProPhoto RGB" JPEGs

[t3dc]

Hey folks,

This is a cross-post of an issue I opened over on the nextcloud support channel but I thought this might be a better place to post and get an answer.

I have a series of photos an event photographer is providing me that I would like to share with family using our family nextcloud. Here's the problem, the previews get the colors wrong:

As you can see in the example above, skin tones move from normal and healthy looking to something like the zombie apocalypse.

The source jpegs display beautifully on my computer after syncing from NextCloud, but the previews all look like they do above. I've deleted and recreated all of the previews at command-line (using previewgenerator) and I've followed the guides for changing NextCloud's default previewing behavior. The results remain as above. If I upload a jpeg from my camera, it looks fine. Only jpegs coming from the photographer have an issue. That's what got me looking at color profiles.

The photog is using "ProPhoto RGB" as her colorspace. When I create jpegs, I'm using "sRGB." I can convert her photos from "ProPhoto RGB" to "sRGB" and they preview properly -- but of course there is some generation loss.

Can anyone help me figure out how to generate proper previews from the ProPhoto RGB files? Or even manually replace previews with a batch export from some other program?

Thanks!

[ShaunCurrier]

Definitely smells like what would happen if the preview generator doesn't respect the color profile when generating the preview. Instead, it seems like it's reading the image data naively and treating it as though it is sRGB. In my experience, when non-color-space-aware apps open large color space images the result is colors that look washed-out and lack saturation. Just like what you show.

Sorry, I can't propose a solution, but thought +1'ing the problem might help eventually.

[t3dc]

Thanks. In the end, I had the photographer provide two copies, one in sRGB for display and a separate set for print. Would love to see this get fixed, though.

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Sent from my iPhone

On 1 Feb 2022, at 05:23, ShaunCurrier ***@***.***> wrote:  Definitely smells like what would happen if the preview generator doesn't respect the color profile when generating the preview. Instead, it seems like it's reading the image data naively and treating it as though it is sRGB. In my experience, when non-color-space-aware apps open large color space images the result is colors that look washed-out and lack saturation. Just like what you show. Sorry, I can't propose a solution, but thought +1'ing the problem might help eventually. — Reply to this email directly, view it on GitHub, or unsubscribe. Triage notifications on the go with GitHub Mobile for iOS or Android. You are receiving this because you authored the thread.

[st3iny]

This seems to be an issue with gd and more specifically libgd. There is already an open ticket about this issue at libgd/libgd#136.

Sadly, there is not much I can do right now. As long as the server code is using gd to generate previews we are stuck with this issue.

[t3dc]

Thanks, Richard. I appreciate your following up. Hopefully, we’ll see a fix in gd. :)

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On Feb 1, 2022, at 4:32 PM, Richard Steinmetz ***@***.***> wrote: This seems to be an issue with gd and more specifically libgd. There is already an open ticket about this issue at libgd/libgd#136 <libgd/libgd#136>. Sadly, there is not much I can do right now. As long as the server code is using gd to generate previews we are stuck with this issue. — Reply to this email directly, view it on GitHub <#201 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AMTXYKQHUF37JKERYZZL5OTUZADJJANCNFSM4PHNRAVA>. Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>. You are receiving this because you authored the thread.

[joshtrichards]

Duplicate of nextcloud/server#22951