Fix scaling small images in the multi source with bicubic smoothing

We need a bigger border or some areas are zero.  Also, fix corner
computation.

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Change Log
 
+## 1.29.8
+
+### Bug Fixes
+
+- Fix scaling small images in the multi source with bicubic smoothing ([#1627](../../pull/1627))
+
 ## 1.29.7
 
 ### Improvements

sources/multi/large_image_source_multi/__init__.py

@@ -1071,7 +1071,7 @@ def _getTransformedTile(self, ts, transform, corners, scale, frame, crop=None):
         # we only need every 1/srcscale pixel.
         srcscale = int(2 ** math.log2(max(1, srcscale)))
         # Pad to reduce edge effects at tile boundaries
-        border = int(math.ceil(2 * srcscale))
+        border = int(math.ceil(4 * srcscale))
         region = {
             'left': int(max(0, minx - border) // srcscale) * srcscale,
             'top': int(max(0, miny - border) // srcscale) * srcscale,
@@ -1119,8 +1119,8 @@ def _getTransformedTile(self, ts, transform, corners, scale, frame, crop=None):
         # Recompute where the source corners will land
         destcorners = (np.dot(transform, regioncorners.T).T).tolist()
         destShape = [
-            max(max(math.ceil(c[1]) for c in destcorners), srcImage.shape[0]),
             max(max(math.ceil(c[0]) for c in destcorners), srcImage.shape[1]),
+            max(max(math.ceil(c[1]) for c in destcorners), srcImage.shape[0]),
         ]
         if max(0, -x) or max(0, -y):
             transform[0][2] -= max(0, -x)

test/test_source_multi.py

@@ -274,13 +274,13 @@ def testMultiAffineTransform():
     source = large_image_source_multi.open(imagePath)
     frameval = [
         [243, 243, 49065],
-        [3920, 3920, 47672],
-        [13, 13, 49149],
-        [3943, 3943, 47695],
-        [246, 246, 49063],
-        [972, 972, 48785],
-        [1455, 1455, 48597],
-        [204, 204, 49059],
+        [3924, 3924, 47676],
+        [13, 13, 49148],
+        [2592, 2592, 48093],
+        [235, 235, 49062],
+        [942, 942, 48785],
+        [1014, 1014, 48872],
+        [198, 198, 49063],
     ]
     for frame in range(8):
         thumbs = {}
@@ -292,9 +292,9 @@ def testMultiAffineTransform():
             r = np.sum(img[:, :, 0] >= 128)
             g = np.sum(img[:, :, 1] >= 128)
             b = np.sum(img[:, :, 2] >= 128)
-            assert abs(r - frameval[frame][0]) < 200
-            assert abs(g - frameval[frame][1]) < 200
-            assert abs(b - frameval[frame][2]) < 200
+            assert abs(r - frameval[frame][0]) < 250
+            assert abs(g - frameval[frame][1]) < 250
+            assert abs(b - frameval[frame][2]) < 250
         assert abs(np.average(thumbs[2048] - thumbs[256])) < 7
         assert abs(np.average(thumbs[1024] - thumbs[256])) < 7
         assert abs(np.average(thumbs[512] - thumbs[256])) < 7