https://bugs.kde.org/show_bug.cgi?id=429219
Bug ID: 429219
Summary: MWG "Applied To" state (mwg-rs:AppliedToDimensions XMP
tag) is not included when writing Face metadata to
file
Product: digikam
Version: 7.1.0
Platform: Other
OS: Other
Status: REPORTED
Severity: normal
Priority: NOR
Component: Metadata-Xmp
Assignee: digikam-bugs-n...@kde.org
Reporter: jose_oli...@hotmail.com
Target Milestone: ---
SUMMARY
MWG mwg-rs:AppliedToDimensions XMP tag is not included when writting Face
metada to file. These values are important in determining if the face regions
are valid for the image.
STEPS TO REPRODUCE
1. Using a photo with a face, scan for face.
2. Add name details to face region.
3. Write face metadata to image file.
OBSERVED RESULT
Using a metadata extraction tool such as exiftool, extract XMP.
Example: exiftool <filename> -xmp -b > output.xml
Face data is added within mwg-rs:Regions
mwg-rs:AppliedToDimensions XMP tag with image height and width dimensions are
not included.
EXPECTED RESULT
- Per MWG (Metadata Working Group) Guidelines for Handling Image Metadata
version 2.0 page 53 - the mwg-rs:AppliedToDimensions field should contain
"Width and height of the image at the time of processing when storing image
region
metadata."
- Why is this important/useful? When an image is cropped, rotated and/or
resized using an application which does not re-adjust the MWG file regions the
regions risk being offset. An application can compare the recorded
mwg-rs:AppliedToDimensions with the actual image dimensions to determine if the
face regions are valid or not.
- In the event that the AppliedToDimensions and actual image dimensions do not
match, Digikam may choose to ignore/invalidate the face regions so they can be
re-applied.
- In the event an image is resized, cropped or rotated, Digikam should adjust
the image regions accordingly and reset the AppliedToDimensions value.
- Another risk is that an application which does read MWG regions may ignore
the face regions added by Digikam, based on the assumption that these are
invalid or do not adhere to the MWG guidelines.
Refer to Page 55:
“Applied To” State
Since the file may be modified by actors that are either non-compliant to this
guidance or choose not
to participate in image region metadata, it is critical to retain information
about what the state of the
image was when the region was specified. A Creator MUST store the region
“applied to” width and
height.
A Changer MUST update the “applied to” value upon a resize, crop, or physical
rotation in order to
ensure that the region information is still valid for the new state of the
file. In the case of a crop or
physical rotation, a Changer MUST also update the region coordinates so as to
further ensure that the
region information remains valid. A Changer SHOULD remove region information
for regions that are
no longer applicable (e.g. a region that was orphaned due to a crop or rotation
operation).
A Consumer MUST validate the current state of the image and compare this
against the “applied to”
state to ensure that the region information is up-to-date. The information
specified in the region MUST
be validated to ensure that the data is applicable to the current state of the
file. In the case where the
“applied to” size and actual image size differ, if the ratio is significantly
different a Consumer SHOULD
ignore the region. Otherwise a Consumer or Changer MAY update the region
metadata as though
the image were scaled to the new dimensions.
SOFTWARE/OS VERSIONS
Windows: 10
macOS:
Linux/KDE Plasma:
(available in About System)
KDE Plasma Version:
KDE Frameworks Version:
Qt Version:
ADDITIONAL INFORMATION
References:
https://www.exiv2.org/tags-xmp-mwg-rs.html
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