Lossless rotation makes incorrect change - rotate left does 180°

[calberga]

For some time now, in the Thumbnail View, when I right-click a thumbnail of a photo in portrait orientation, then hover on "JPG lossless operation" and right-click "...(to left)...", the thumbnail (and the .jpg viewed in Irfanview) rotates 180°. I then have to repeat, and right-click "..(to right).." This is happening with photos taken with a Lumix point-and-shoot camera and with an iPhone. In fact, it is stranger than that. Trying a sequence that I had never used in practice (while writing this) I would that starting with a portrait image, the first ...(to left)... command inverts the image (180°) but repeating the ...(to left)... behaves correctly the nest two times, with 3 rotations to the left acting like 4. But after that sequence ...(to left)... works correctly on that image. So, it seems (and I probably haven't tried enough cases to prove this) the first time a portrait image is losslessly rotated to the left it actually performs a 180° rotation, but from then on things work all right. What other information (I assume, from the EXIF) is needed? --- Okay, I have something: in a photo that has not been touch the EXIF orientation is "right top", but in one that has been rotated 360° (by 3 90° turns!) the orientation is "top left". Is this enough to find an explanation?

Sorry to wind up giving a blow-by-blow debugging run.

[Bhikkhu Pesala]

See Settings, JPG/PCD/GIF, Autorotate images according to EXIF info.

[calberga]

That is, and has been, checked. Are you suggesting that I uncheck it?

[Bhikkhu Pesala]

Yes, uncheck it, and see if that fixes the issue.

[calberga]

No, the initial 180° rotation still occurs on the first "...(to Left)..." command.

[calberga]

NB: I am using IrfanView Version 4.60 - 64 bit.

[Bhikkhu Pesala]

The latest version is 4.62. I cannot reproduce the issue. Can you share the image with us?

[calberga]

First: Updated to 4.62, which did not make a difference.
Second: Yes, unchecking the Autorotate option does "fix" the problem. However, it also leaves me with hundreds (at a minimum) of images which now must be re-rotated. I've rechecked the box. Is there a way to do a bulk lossless rotate of the images (with the box unchecked)? Other wise I guess I have to live with the crazy first-time LL left rotate. I don't have the energy, nor the time to go through all the affected images.

[Bhikkhu Pesala]

In the thumbnail view, the option is lossless rotation with selected images.

[calberga]

That I am aware of, but I have the images scattered into dozens, of directories and sub-directories, with at least three differently organized trees, with different file names in each. About 80,000 images in up to 3,000 directories, plus separate thumbnail files in one of the sets. So, "lossless rotation with selected images" is a bit of a non-starter.

If I use EXIFtools to extract information from the images, is there a simple algorithm to tell what, if any, rotation is needed to get the image into the state where lossless rotation works as expected? Given that, is there a way to invoke the rotation from a batch file? If so I could throw together a p program to scan all the images and applies the needed action. I really didn't want to have to delve into the EXIF tags, but perhaps I must.