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EXIF orientation info in PNGs isn't used for image-orientation: from-image

bugzilla.mozilla.org

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Re: EXIF orientation info in PNGs isn't used for image-orientation: from-image

#41

Post by netsharc »

postalcoder wrote: post #14

As a former metadata completionist, my mind starts to dissociate when I think about my battles with EXIF metadata, vendor-specific metadata, and the way different software supports, or refuses to support, any of it. It gets even worse when ingesting images into Apple Photos, where you have to confront papercut bugs that you know will never be fixed. I love ExifTool. It’s one of the great utilities. It works for almos…

I guess orientation isn't even metadata any more, but data: the RGB(A) value of each pixel is data, and the location of this pixel is also data. But the location of the pixel changes depending on the orientation. Of course absent of any orientation it can be understood as "information of the image is stored in the file describing the image" in left-to-right, top-to-bottom order (but with BMPs it's bottom to top!), but with orientation "metadata", it's whatever is defined there.

So yeah, I think "Stripping all EXIF metadata doesn't change an image" deserves an entry as a "falsehood programmers believe about...".

Re: EXIF orientation info in PNGs isn't used for image-orientation: from-image

#42

Post by stackedinserter »

mzur wrote: post #26

Browsers starting to rotate images based on EXIF is such a pain. I maintain an image annotation tool and all of a sudden images were shown differently to users depending on the browser they used. Then you have to jump through all sorts of hoops to ignore the EXIF orientation again. In some cases you are not allowed to see if the orientation was changed for security reasons. And then the only way to control this is th…

I maintain a photo library project, I feel your pain. JPEG format is so crooked in so many ways.

It's shame that after so many years of development we ended up with such horrible formats like jpeg and mp4.

Re: EXIF orientation info in PNGs isn't used for image-orientation: from-image

#43

Post by justincormack »

circuit10 wrote: post #37
coldpie wrote: post #35

Earlier quoted context omitted.

Yes. I wrote a little image uploader script to easily upload images from my phone for embedding in web forums etc, and it strips out all the EXIF orientation and just converts it to the correct orientation. Aside from that I'm always having to fiddle with it in my image tools and hope every software I use supports it. It's such a crap feature. Just rotate the damn image, phones!

Wouldn’t that degrade the quality for a lossy format, especially if done repeatedly? I see why people would not want their phone to do that. If you’re uploading it somewhere that might not be supported it would be worth it but I don’t want my phone to silently degrade images that are just sitting in my gallery

JPEG allows for lossless 90 degree rotation, not sure about other formats

Re: EXIF orientation info in PNGs isn't used for image-orientation: from-image

#44

Post by lukan »

moron4hire wrote: post #4
LiamPowell wrote: post #2

See also: The VLC bug that incorrectly applies right crops as left crops [1]. This bug report is from 2023, however the bug has existed as long as VLC has as far as I know. I'm always surprised to see bugs like this where an extremely easy to test part of the spec just seemingly isn't tested and ends up as a bug that never gets fixed until many years later. [0]: https://code.videolan.org/videolan/vlc/-/issues/28279

I firmly believe every product team needs to be split in two: one half works on the issue of highest importance, the other works on the easiest issues. If only to avoid the embarrassment of easy to fix bugs that were passed over for eons just because they weren't priority-high.

That will be great popcorn stuff to watch from the outside I think.

Or tragic, but I rather see drama than joy with this approach. The main thing with bugfixing is, that it can affect a whole lot of other areas, or introduce completely new bugs. So both teams then fighting over changes ..

Now a really trivial bug with no side effects, sure thing, no issue, but like a sibling commentor has said, the really trivial bugs are usually fixed already. And quick fixes of seemingly trivial things can induce a world of pain for someone else.

In other words, I think project management and prioritising things remain hard, with no magic bullets solutions avaiable. (But I wpuld also prefer a stronger emphasis on quality control in general, vs new feature)

Re: EXIF orientation info in PNGs isn't used for image-orientation: from-image

#45

Post by pavlov »

netsharc wrote: post #41
postalcoder wrote: post #14

As a former metadata completionist, my mind starts to dissociate when I think about my battles with EXIF metadata, vendor-specific metadata, and the way different software supports, or refuses to support, any of it. It gets even worse when ingesting images into Apple Photos, where you have to confront papercut bugs that you know will never be fixed. I love ExifTool. It’s one of the great utilities. It works for almos…

I guess orientation isn't even metadata any more, but data: the RGB(A) value of each pixel is data, and the location of this pixel is also data. But the location of the pixel changes depending on the orientation. Of course absent of any orientation it can be understood as "information of the image is stored in the file describing the image" in left-to-right, top-to-bottom order (but with BMPs it's bottom to top!), bu…

The same applies to color space. You can’t interpret the pixel data without knowing the color space. If it’s not in the metadata, you just have to assume sRGB and hope for the best.

It’s the same with rotation. Both are essential information on how to interpret the pixel data for display, but we’re so very used to assuming certain defaults that it’s easy to forget about this.

Re: EXIF orientation info in PNGs isn't used for image-orientation: from-image

#49

Post by Aardwolf »

alexdbird wrote: post #23

I personally like the status quo that PNGs don't encode orientation. I can dump PNGs when I'm debugging and I know I'm looking at the bits the same way up as the code is!

PNG now does - and they've been as vague as they could be in the spec about whether any exif data should affect the image display or not. The spec says:

"It is recommended that unless a decoder has independent knowledge of the validity of the Exif data, the data should be considered to be of historical value only."

Instead of either saying: "yes you must rotate it" or "no you shall not rotate it" to make everyone do the same thing. And if it were yes, they should also have made this a mandatory chunk since now they made it optional to read.

Re: EXIF orientation info in PNGs isn't used for image-orientation: from-image

#50

Post by seam_carver »

I once had to deal with an old website that ignored the orientation flag in jpg, so my iPhone portrait photos showed up landscape when I uploaded them.

Thankfully Finder in macOS has a way to remove the flag:

How to remove orientation from portrait photo from iPhone on macOS https://youtu.be/lWOlfjVyes4

I couldn’t find a way to do it in Preview, but Finder could do it.

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