Difference between rotation and lossless rotation?

[andrea.ippo]

Can someone tell me what it is?

[marsh]

The browser option. With jpeg, Pierre uses a special method to directly rotate image without the need of re-saving it first. Avoiding a loss in content (which is the case when people re-save same jpeg over and over at 75% setting, as an example).
Normal rotation is also lossless if the format (like png) is also lossless one (unlike jpeg).

[andrea.ippo]

The browser option. With jpeg, Pierre uses a special method to directly rotate image without the need of re-saving it first. Avoiding a loss in content (which is the case when people re-save same jpeg over and over at 75% setting, as an example).
Normal rotation is also lossless if the format (like png) is also lossless one (unlike jpeg).

So please tell me if I'm right.
Assuming I'm only interested in handling JPEGs:

in browser view, the "simple" rotation is equivalent to the one accessible via the "lossless jpeg transformations" button, and immediately saves the changes to the file. Thus, in this view you can use both commands
In the other view, the "simple" rotation is not lossless, but uses the compression % set in the options for the JPEG format, and the original file is unchanged until you overwrite it by saving changes. In this view, the only way to achieve lossless rotation is by clicking the "lossless jpeg transformations" button. In this case, again, the changes are immediately applied to the original file

Can you confirm?
Thanks

[marsh]

The browser option. With jpeg, Pierre uses a special method to directly rotate image without the need of re-saving it first. Avoiding a loss in content (which is the case when people re-save same jpeg over and over at 75% setting, as an example).
Normal rotation is also lossless if the format (like png) is also lossless one (unlike jpeg).

So please tell me if I'm right.
Assuming I'm only interested in handling JPEGs:

in browser view, the "simple" rotation is equivalent to the one accessible via the "lossless jpeg transformations" button, and immediately saves the changes to the file. Thus, in this view you can use both commands
In the other view, the "simple" rotation is not lossless, but uses the compression % set in the options for the JPEG format, and the original file is unchanged until you overwrite it by saving changes. In this view, the only way to achieve lossless rotation is by clicking the "lossless jpeg transformations" button. In this case, again, the changes are immediately applied to the original file

Can you confirm?
Thanks

Yes for both. You have choice of 2 methods in browser view (which change file immediately).
Options>Browser>Misc>[x]Use Lossless rotation when possible (JPEG)

[andrea.ippo]

All right, thank you

[Dreamer]

Just a hint - you may use the (hidden) keyboard shortcut Ctrl+Right (or Left) to rotate the image in viewer and fullscreen (edit mode only) - when using together with Left/Right to go to prev./next image it's possibly the best way to quickly rotate images.

Also try the option in the "lossless jpeg transformations" button menu > "Rotate based on EXIF value". First select all files in browser (Ctrl+A), then use this option. It's not working with all pictures, in that case you'll have to do it manually.

[aussenboarder]

hello.
just to make sure i understand right:

the rotation cw/ccw buttons ...

... that are available in the browser and the viewer
both rotate any jpeg file in lossless mode when the option ...
browser / misc / use lossless rotation when possible (jpeg) is checked?

so the 2 buttons are doing the same operation as the jpeg lossless transformation ...

... would do for jpeg files.

can you please confirm or confute?!
cheers, aussenboarder

[xnview]

If you have checked browser / misc / use lossless rotation when possible (jpeg), the rotation in browser make a lossless rotation on jpeg

[aussenboarder]

@Pierre
is there a reason that the same does not apply to the viewer?

[Dreamer]

@Pierre
is there a reason that the same does not apply to the viewer?

Confirmed - but rotation doesn't work at all also in Browser - even is that option is disabled, using toolbar buttons.

[xnview]

@Pierre
is there a reason that the same does not apply to the viewer?

In Browser, you work on file, in Viewer on image data

Confirmed - but rotation doesn't work at all also in Browser - even is that option is disabled, using toolbar buttons.

???

[aussenboarder]

@Pierre
can you please explain what happens when i use the rotate commands in the viewer? the same commands can be found in both interfaces (browser, viewer).
i experience two different behaviours:
case 1: when i use the "normal" rotate commands in the viewer the program asks me whether i want to safe the changes as soon as i change to the browser.
case 2: when i use the "lossless" rotate commands in the viewer the program rotates the image and takes over the changes without asking.
what is the difference between working "on file" and "on image data"?

thank you for you fast reply! regards, aussenboarder

[xnview]

what is the difference between working "on file" and "on image data"?

If you work on the file (only jpeg), the file is changed. If you work on image data, the original file is not changed...

[aussenboarder]

hi Pierre.
i see the difference in handling the image data in the memory instead of directly reading and writing on the file. (pls correct me if i misunderstood)

but i do not understand the following:
i did an experiment rotating an image with the 4 different modes.
the result is that only the "normal" mode of the viewer keeps the original data. the other modes cut off pixels whenever the image dimension aren't a multiple of 8 (?)



why is the above described cut off happening?
what is so special about the 8 pixel multiple?
does it occur for both dimensions?
why are the rotation modes working different?

please do not take this as an offense - i just do not understand and i am curious. rgds, aussenboarder

[Dreamer]

Confirmed - but rotation doesn't work at all also in Browser - even is that option is disabled, using toolbar buttons.

???

In Browser, regardless of "use lossless rotation when possible (jpeg)" option, when I click the "Rotate clockwise" toolbar button, nothing happens, image is not rotated, preview just blinks.

In Viewer, if option "use lossless rotation when possible (jpeg)" is enabled, lossless rotation is not used when I use "Rotate clockwise" toolbar button, but image is rotated.