Question to various rotate

[herb]

Hello,

I work with XnViewMP 0.80.
Customizing my toolbars I have seen that for rotate90/180/270 XnViewMP has the possibility to select 2 (different) commands:
- cmd_rotate90/180/270 and
- cmd_lrotate90/180/270 (with a "l" before rotate)

Can someone explain to me what is the difference between the 2 commands?
Which command is used by menu in browser mode and which command is used by menu in view mode?

Thanks in advance
Best regards
Herb

[XnTriq]

Hello Herb

While cmd_rotate* can be used on all image formats, the cmd_lrotate* commands (Tools » JPEG lossless transformations) only work for JPEG files.

The behavior of the “regular” rotate commands is customizable:

• Tools » Settings...
  • General » File operations » Keep original date/time
    • Lossless transformations
  • Browser » Misc. » Rotation
    • Change EXIF orientation ONLY (if possible)
    • Use lossless rotation (if possible)

[herb]

Hello XnTriq,

thanks for quick reply.

My interpretation of "lossless rotation" is as follows:
- pixels of the *.jpg file are rearranged
- exif tag orientation remains unchanged
- tags image-width and image-height are exchanged ( in case of rotate +90/-90)

Taking this as the criteria I do not agree to your info:
Tools » Settings... -> General » File operations » Keep original date/time: (always) Lossless transformations

I have checked all (3) checkboxes for these settings and
I performed a rotation-"change EXIF orientation only" with cmd_rotate (without l).

So I suggest the date/time change does not depend on the rotate method.

Best regards
Herb

[XnTriq]

My interpretation of "lossless rotation" is as follows:
- pixels of the *.jpg file are rearranged
- exif tag orientation remains unchanged
- tags image-width and image-height are exchanged ( in case of rotate +90/-90)

Yes, the EXIF orientation tag should only be reset to 1 (top/left), if we use cmd_lrotateExif (Rotate based on EXIF orientation field = rearranging of pixels = “transcoding”) or cmd_lresetExif (pixels are not rearranged).

Taking this as the criteria I do not agree to your info:
Tools » Settings... -> General » File operations » Keep original date/time: (always) Lossless transformations

I have checked all (3) checkboxes for these settings and
I performed a rotation-"change EXIF orientation only" with cmd_rotate (without l).

So I suggest the date/time change does not depend on the rotate method.

Sorry, I'm not sure if I understand correctly. Do you mean that the info isn't correct or that there's a bug?

XnView Classic (for comparison):

There are actually three settings:

1. Tools » Options... » General » File Operations » Keep date/time for saving
2. Tools » Options... » Browser » Misc. » Rotation » Keep original date/time attributes
3. Tools » Batch Processing... » Output » Keep original date/time attributes

Related topics:

• Lossless JPEG cropping doesn't change date/time stamp
• File date not updating

- 'Keep original date/time attributes' is unnecessary, IMO, as already available in GENERAL>File Operations ('keep date/time for saving').
- What is 'Use Lossless rotation when possible (JPEG)' for?

[XnTriq]

1. Download Karl02's suite of test images (exif-orientation-testimages-v2.rar).
2. Extract F2_5.jpg (EXIF orientation: 5 = left/top).
3. Remove the write protection attribute from F2_5.jpg.
4. Make a copy of F2_5.jpg.
5. Rename F2_5.jpg to cmd_rotate90.jpg,
   and Copy of F2_5.jpg to cmd_lrotate90.jpg.
6. Start XnViewMP.
7. Make sure the following settings are activated:
   • General » File operations » Keep original date/time
     • Lossless transformations
   • Browser » Misc. » Rotation
     • Change EXIF orientation ONLY (if possible)
     • Use lossless rotation (if possible)
8. Select the thumbnail of cmd_lrotate90.jpg in the browser and hit Ctrl+Shift+R (= cmd_lrotate90).
   1. Warning message: “JPEG lossless operation will modify original file(s), and may remove some unused pixels (width and height must be multiple of 8 pixels)! Do you want to continue?”
   2. The image is rotated 90° clockwise.
   3. The dimensions are changed from W255×H239 to W224×H255.
   4. The EXIF orientation flag is reset to 1 (top/left).
   5. The file's timestamp remains the same.
9. Select the thumbnail of cmd_rotate90.jpg in the browser and click the Rotate clockwise (= cmd_rotate) button on the main toolbar.
   • No changes are made to the file
     Expected behavior: Steps 8a through 8e

[herb]

Hello XnTriq,

again thanks for your detailed answers.
And Yes I performed some more tests as you described in your last post.

Also the following part of your first answer is now clear to me:

Tools » Settings... » General » File operations » Keep original date/time
Lossless transformations

I works as expected:
- In case of "keep date/time" is unchecked, XnViewMP does not perform a lossless rotation by itself.
- You can also perform a rotation with only exif:orientation changed.

But the problem is the following reading of metadata:
Because file creation-date of file in filesystem and "exif:data/time original" is different,
XnViewMP always displays exif:date taken with value 1=normal=topleft
(Exiftool display the correct value after a rotation)

So I agree: in this case alsways a lossless rotation should be performed by user.
Question: Is the above described problem a known issue or do we have to open another topic?

Thanks again and
Best regards
Herb

[XnTriq]

Sorry for the delay, Herb

Also the following part of your first answer is now clear to me:

Tools » Settings... » General » File operations » Keep original date/time
Lossless transformations

I works as expected:
- In case of "keep date/time" is unchecked, XnViewMP does not perform a lossless rotation by itself.
- You can also perform a rotation with only exif:orientation changed.

Thanks for confirming!

But the problem is the following reading of metadata:
Because file creation-date of file in filesystem and "exif:data/time original" is different,
XnViewMP always displays exif:date taken with value 1=normal=topleft
(Exiftool display the correct value after a rotation)

I see you've posted a bug report (EXIF:orientation is always top-left(1)), …

Question: Is the above described problem a known issue or do we have to open another topic?

… and so did I ("cmd_rotate" & "Change EXIF orientation ONLY")