Saturday, December 26, 2015

JPG Surprise: Rotation might not be real

Today I was working with a Micca M703, a digital picture frame that does slideshows from JPG files on flash drives. It gave me some problems with image rotation; some images displayed sideways on the Micca but correctly on my computer. Research indicated that the Micca doesn't do any auto-rotation to fit the screen, so I was quite confused.

It turns out that I when I rotated the images on my computer (using the convenient context menu items Windows provides for pictures), the image data wasn't transformed, but some bit was set somewhere that causes well-behaved programs to treat the image as if it had actually been rearranged. The Micca doesn't, apparently, respect that option.

So, I had to open each such picture and resave it with Paint.NET to actually rotate the image in its data.

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