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Ignacio Serantes
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xmpmanager.py
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168
xmpmanager.py
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"""
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XMP Manager Module for Bagheera.
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This module provides a dedicated class for handling XMP metadata, specifically
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for reading and writing face region information compliant with the Metadata
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Working Group (MWG) standard. It relies on the `exiv2` library for all
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metadata operations.
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Classes:
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XmpManager: A class with static methods to interact with XMP metadata.
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Dependencies:
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- python-exiv2: The Python binding for the exiv2 library. The module will
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gracefully handle its absence by disabling its functionality.
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- utils.preserve_mtime: A utility to prevent file modification times from
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changing during metadata writes.
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"""
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import os
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import re
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from utils import preserve_mtime
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from metadatamanager import notify_baloo
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try:
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import exiv2
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except ImportError:
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exiv2 = None
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class XmpManager:
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"""
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A static class that provides methods to read and write face region data
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to and from XMP metadata in image files.
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"""
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@staticmethod
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def load_faces(path):
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"""
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Loads face regions from a file's XMP metadata (MWG Regions).
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This method parses the XMP data structure for a `mwg-rs:RegionList`,
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extracts all regions of type 'Face', and returns them as a list of
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dictionaries. Each dictionary contains the face's name and its
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normalized coordinates (center x, center y, width, height).
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Args:
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path (str): The path to the image file.
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Returns:
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list: A list of dictionaries, where each dictionary represents a face.
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Returns an empty list if exiv2 is not available or on error.
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"""
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if not exiv2 or not path or not os.path.exists(path):
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return []
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faces = []
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try:
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img = exiv2.ImageFactory.open(path)
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# readMetadata() is crucial to populate the data structures.
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img.readMetadata()
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xmp = img.xmpData()
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regions = {}
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for datum in xmp:
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key = datum.key()
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if "mwg-rs:RegionList" in key:
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# Use regex to find the index of the region in the list,
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# e.g., RegionList[1], RegionList[2], etc.
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m = re.search(r'RegionList\[(\d+)\]', key)
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if m:
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idx = int(m.group(1))
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if idx not in regions:
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regions[idx] = {}
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val = datum.toString()
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if key.endswith("/mwg-rs:Name"):
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regions[idx]['name'] = val
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elif key.endswith("/stArea:x"):
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regions[idx]['x'] = float(val)
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elif key.endswith("/stArea:y"):
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regions[idx]['y'] = float(val)
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elif key.endswith("/stArea:w"):
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regions[idx]['w'] = float(val)
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elif key.endswith("/stArea:h"):
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regions[idx]['h'] = float(val)
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elif key.endswith("/mwg-rs:Type"):
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regions[idx]['type'] = val
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# Convert the structured dictionary into a flat list of faces,
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# preserving all regions (including 'Pet', etc.) to avoid data loss.
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for idx, data in sorted(regions.items()):
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if 'x' in data and 'y' in data and 'w' in data and 'h' in data:
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faces.append(data)
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except Exception as e:
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print(f"Error loading faces from XMP: {e}")
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return faces
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@staticmethod
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def save_faces(path, faces):
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"""
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Saves a list of faces to a file's XMP metadata as MWG Regions.
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This method performs a clean write by first removing all existing
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face region metadata from the file and then writing the new data.
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This method preserves the file's original modification time.
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Args:
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path (str): The path to the image file.
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faces (list): A list of face dictionaries to save.
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Returns:
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bool: True on success, False on failure.
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"""
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if not exiv2 or not path:
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return False
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try:
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# Register required XMP namespaces to ensure they are recognized.
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exiv2.XmpProperties.registerNs(
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"http://www.metadataworkinggroup.com/schemas/regions/", "mwg-rs")
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exiv2.XmpProperties.registerNs(
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"http://ns.adobe.com/xmp/sType/Area#", "stArea")
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with preserve_mtime(path):
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img = exiv2.ImageFactory.open(path)
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img.readMetadata()
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xmp = img.xmpData()
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# 1) Remove all existing RegionList entries to prevent conflicts.
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keys_to_delete = [
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d.key() for d in xmp
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if d.key().startswith("Xmp.mwg-rs.Regions/mwg-rs:RegionList")
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]
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for key in sorted(keys_to_delete, reverse=True):
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try:
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xmp_key = exiv2.XmpKey(key)
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it = xmp.findKey(xmp_key)
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if it != xmp.end():
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xmp.erase(it)
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except Exception:
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pass
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# 2) Recreate the RegionList from the provided faces list.
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if faces:
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# To initialize an XMP list (rdf:Bag), it is necessary to
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# register the key as an array before it can be indexed.
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# Failing to do so causes the "XMP Toolkit error 102:
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# Indexing applied to non-array". A compatible way to do
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# this with the python-exiv2 binding is to assign an
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# XmpTextValue and specify its type as 'Bag', which
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# correctly creates the empty array structure.
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if exiv2 and hasattr(exiv2, 'XmpTextValue'):
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xmp["Xmp.mwg-rs.Regions/mwg-rs:RegionList"] = \
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exiv2.XmpTextValue("type=Bag")
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for i, face in enumerate(faces):
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# The index for XMP arrays is 1-based.
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base = f"Xmp.mwg-rs.Regions/mwg-rs:RegionList[{i+1}]"
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xmp[f"{base}/mwg-rs:Name"] = face.get('name', 'Unknown')
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xmp[f"{base}/mwg-rs:Type"] = face.get('type', 'Face')
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area_base = f"{base}/mwg-rs:Area"
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xmp[f"{area_base}/stArea:x"] = str(face.get('x', 0))
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xmp[f"{area_base}/stArea:y"] = str(face.get('y', 0))
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xmp[f"{area_base}/stArea:w"] = str(face.get('w', 0))
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xmp[f"{area_base}/stArea:h"] = str(face.get('h', 0))
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xmp[f"{area_base}/stArea:unit"] = 'normalized'
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img.writeMetadata()
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notify_baloo(path)
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return True
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except Exception as e:
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print(f"Error saving faces to XMP: {e}")
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return False
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