Do not attempt to resize images to dimensions larger than their polygon for thumbnails

arkindex/documents/models.py

@@ -656,9 +656,11 @@ class Element(IndexableModel):
         if self.mirrored:
             rotation_param = f"!{rotation_param}"
 
+        # Do no attempt to upsize small images for thumbnails
+        thumbnail_height = min(400, height)
         return urljoin(
             self.image.url + "/",
-            f"{x},{y},{width},{height}/,400/{rotation_param}/default.jpg"
+            f"{x},{y},{width},{height}/,{thumbnail_height}/{rotation_param}/default.jpg"
         )
 
     def __str__(self):

arkindex/documents/tests/test_element.py

@@ -38,24 +38,22 @@ class TestElement(FixtureTestCase):
 
     def test_iiif_thumbnail_url(self):
         cases = [
-            (0, False, "http://server/img1/10,20,30,40/,400/0/default.jpg"),
-            (0, True, "http://server/img1/10,20,30,40/,400/!0/default.jpg"),
-            (180, False, "http://server/img1/10,20,30,40/,400/180/default.jpg"),
-            (180, True, "http://server/img1/10,20,30,40/,400/!180/default.jpg"),
+            (0, False, [[500, 100], [650, 100], [650, 800], [500, 800], [500, 100]], "http://server/img1/500,100,150,700/,400/0/default.jpg"),
+            (0, True, [[500, 100], [650, 100], [650, 800], [500, 800], [500, 100]], "http://server/img1/500,100,150,700/,400/!0/default.jpg"),
+            (180, False, [[500, 580], [650, 580], [650, 700], [500, 700], [500, 580]], "http://server/img1/500,580,150,120/,120/180/default.jpg"),
+            (180, True, [[500, 580], [650, 580], [650, 700], [500, 700], [500, 580]], "http://server/img1/500,580,150,120/,120/!180/default.jpg"),
+            (0, False, [[10, 20], [40, 20], [40, 60], [10, 60], [10, 20]], "http://server/img1/10,20,30,40/,40/0/default.jpg"),
+            (0, True, [[10, 20], [40, 20], [40, 60], [10, 60], [10, 20]], "http://server/img1/10,20,30,40/,40/!0/default.jpg"),
+            (180, False, [[10, 20], [40, 20], [40, 60], [10, 60], [10, 20]], "http://server/img1/10,20,30,40/,40/180/default.jpg"),
+            (180, True, [[10, 20], [40, 20], [40, 60], [10, 60], [10, 20]], "http://server/img1/10,20,30,40/,40/!180/default.jpg"),
         ]
-        for rotation_angle, mirrored, expected_url in cases:
+        for rotation_angle, mirrored, polygon, expected_url in cases:
             with self.subTest(rotation_angle=rotation_angle, mirrored=mirrored):
                 element = Element(
                     name="Something",
                     type=self.element_type,
                     image=self.image,
-                    polygon=[
-                        [10, 20],
-                        [40, 20],
-                        [40, 60],
-                        [10, 60],
-                        [10, 20],
-                    ],
+                    polygon=polygon,
                     rotation_angle=rotation_angle,
                     mirrored=mirrored,
                 )