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

(bugzilla.mozilla.org)
94 points justin-reeves | 2 comments | 21 Nov 25 13:29 UTC | HN request time: 0.4s | source
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postalcoder ◴[21 Nov 25 14:50 UTC] No.46005113[source]▶
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 almost every file I throw at it. But reading its output can be unsettling. It’s like getting a glimpse of eudaimonia, only to have it rudely interrupted by the reality of Apple Photos misreading every lens in your collection.

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1. netsharc ◴[21 Nov 25 15:50 UTC] No.46005609[source]▶
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...".

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2. pavlov ◴[21 Nov 25 15:54 UTC] No.46005647[source]▶
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.