On Tue, 4 Aug 2020 at 17:35:20, Mayayana
wrote:
"J. P. Gilliver (John)" wrote

| Any JPG that requires software to check the
| orientation EXIF tags is a faulty image.
|
| I'm not quite sure what you're saying the if you acknowledge the
| _existence_ of the orientation tag (I didn't know it was part of EXIF
| but that makes sense), then what would you consider its function?

Yes, it's part of EXIF. Bit EXIF is not universally supported
and it's only in JPGs. There's just no reason to need that tag.
The camera can save the image as it's taken. Instead of doing
that they create all sorts on incompatibility. I get a lot of those
sideways images. People don't know because they're seeing it
on their iPhone where they took the picture. I don't understand
why they ever would have used such an idiotic method. Whatever
edge of the camera is up should be the top of the picture.


The reason, I presume, is that it's easier to program the camera's
firmware to just save a flag (as part of a block of EXIF data that it's
saving anyway), than to actually change the order of pixels written into
the file. Originally, also, it may have reduced the need for an extra
block of RAM to hold the image to enable any such rotation to be done;
while memory is now probably cheap enough for that not to be as much of
a problem (though image sizes keep growing insanely so it might still
be!), once the practice had been established, I guess it stuck.

FWIW: when you _do_ get a "sideways image", IrfanView (might need its
plugins, but I always install those anyway) has a "lossless rotation"
function for JPEGs, in other words it can rotate the image without an
extra stage of decompression/recompression and thus degradation. (It
_doesn't_ use the orientation flag: it sets that to the top left of
whatever you rotate to.) Other image handlers can probably do it too;
it's easy in IV, just J enter. (That's shift-J - to bring up the JPEG
utilities menu - and enter to repeat whatever you did last time you
brought up that menu, which in my case is almost always a rotate.)
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

Self Test for Paranoia: You know you have it when you can't think of anything
that's your own fault. - "The Real Bev" in comp.mobile.android, 2019-1-1