fix: Image.metadata() missing camera-specific Exif sub-IFD tags

Image.getexif() (the modern public Pillow API) only returns the
top-level IFD0 tags (Make, Model, Orientation, ...). Camera-specific
tags -- FocalLength, ExposureTime, FNumber, ISOSpeedRatings, LensModel,
etc. -- live in a separate "Exif" sub-IFD that getexif() does not
flatten in. metadata() never fetched that sub-IFD, so
img.metadata("FocalLength") always raised KeyError even though the
tag is genuinely present in the file (confirmed via raw PIL: it's
under Exif.get_ifd(0x8769), the fixed EXIF-spec tag id for the Exif
IFD pointer).

This is a Pillow API evolution, not a data problem: the old private
Image._getexif() used to flatten everything into one dict; the public
getexif() introduced later deliberately does not, requiring an
explicit get_ifd() call for the sub-IFD.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: petercorke

src/machinevisiontoolbox/ImageIO.py

@@ -267,6 +267,14 @@ def metadata(self, key: str | None = None) -> Any:
                 # map tag number to tag name
                 exif[TAGS[tag]] = value
 
+        # Camera-specific tags (FocalLength, ExposureTime, FNumber,
+        # ISOSpeedRatings, LensModel, ...) live in a separate "Exif" sub-IFD
+        # that Image.getexif() does not flatten into the top-level dict --
+        # 0x8769 is the fixed EXIF-spec tag id for the pointer to it.
+        for tag, value in meta.get_ifd(0x8769).items():
+            if tag in TAGS:
+                exif[TAGS[tag]] = value
+
         if key is None:
             return exif
         else:

tests/test_image_io.py

@@ -190,14 +190,23 @@ def test_disp(self):
         # im.disp(block=False)
         pass
 
-    # new test
     def test_metadata(self):
         """Test reading image metadata"""
-        # TODO: Test with image file that has metadata
-        # im = Image.Read('test_image.jpg')
-        # metadata = im.metadata()
-        # self.assertIsNotNone(metadata)
-        pass
+        im = Image.Read("walls-l.png")
+        metadata = im.metadata()
+        self.assertIsNotNone(metadata)
+
+        # top-level IFD0 tags
+        self.assertEqual(metadata["Make"], "Apple")
+        self.assertEqual(metadata["Model"], "iPhone 5s")
+        self.assertEqual(im.metadata("Make"), "Apple")
+
+        # camera-specific tags live in a separate "Exif" sub-IFD that
+        # Image.getexif() doesn't flatten into the top-level dict --
+        # regression test for that sub-IFD merge
+        self.assertIn("FocalLength", metadata)
+        self.assertAlmostEqual(im.metadata("FocalLength"), 4.15)
+        self.assertAlmostEqual(metadata["FNumber"], 2.2)
 
     # new test
     def test_showpixels(self):