JPEG lossless transformations UGLY BUG?

[Mulder]

using xnview 1.80.3 on win2000 or winXP try this:

- create an jpeg file with dimensions for instance 100x50, save it
- open it with xnview, do tools -> JPEG Losseless transformations -> Rotate 90 right (Ctrl+Shift+R)
- now the dimensions will be 48x100!
- do the same three times again, the image will return to it's previous form, but with dimensions 96x48!

I found that this is the same when using "Dialog ..." in JPEG Losseless transformations and checking "Trim image (remove unused pixels)" ... but how this function knows which pixels are unused (if this caused the problems)? In my case it removed possibly useful data from image ...
Anyway if the trim function is there with some intent, this should definitely not be the default manner when rotating using shortcut functions ... because I think everyone who uses this function excepts it just to rotate - not trim ...

[xnview]

using xnview 1.80.3 on win2000 or winXP try this:

- create an jpeg file with dimensions for instance 100x50, save it
- open it with xnview, do tools -> JPEG Losseless transformations -> Rotate 90 right (Ctrl+Shift+R)
- now the dimensions will be 48x100!
- do the same three times again, the image will return to it's previous form, but with dimensions 96x48!

I found that this is the same when using "Dialog ..." in JPEG Losseless transformations and checking "Trim image (remove unused pixels)" ... but how this function knows which pixels are unused (if this caused the problems)? In my case it removed possibly useful data from image ...
Anyway if the trim function is there with some intent, this should definitely not be the default manner when rotating using shortcut functions ... because I think everyone who uses this function excepts it just to rotate - not trim ...

It's normal, for jpeg lossless rotation picture must be multiple of 8/16

[Olivier_G]

It's normal, for jpeg lossless rotation picture must be multiple of 8/16

Well, if you select "lossless rotation" it is obviously that you care about data, and having a certain amount of the picture lost without warning is... bad.

In the rotation dialog, you should have an option "if dimensions are not multiple of 8":
A. Apply lossless rotation on the trimmed 8x8 multiple part +Append lossy rotation of the extra part
B. Fill in with a selected color to get 8x8 multiple before making lossless rotation (1 JPEG compression for the extra modified part would be necessary)
C. Trim to 8x8 multiple
D. Do Nothing
E. Ask with a dialog pop-up
...and this setting should apply when you select any Lossless JPEG operation.

Olivier

[JohnFredC]

jpeg lossless rotation picture must be multiple of 8/16

Of course something like this must be the case but...

I didn't know it before. Good to know now, though! Thanks!

[Dreamer]

It's normal, for jpeg lossless rotation picture must be multiple of 8/16

Well, if you select "lossless rotation" it is obviously that you care about data, and having a certain amount of the picture lost without warning is... bad.

In the rotation dialog, you should have an option "if dimensions are not multiple of 8":
A. Apply lossless rotation on the trimmed 8x8 multiple part +Append lossy rotation of the extra part
B. Fill in with a selected color to get 8x8 multiple before making lossless rotation (1 JPEG compression for the extra modified part would be necessary)
C. Trim to 8x8 multiple
D. Do Nothing
E. Ask with a dialog pop-up
...and this setting should apply when you select any Lossless JPEG operation.

Olivier

I agree, same with lossless crop...

E.g.: show "unusable" resolution in red (in status bar) or allow to select just "usable" resolution.