Fix aspect ratio sampling for RandomResizedCrop (apache#14585)

* added log sampling for aspect ratio

* added test

* added comments

* fix test

* remove math, fix test

python/mxnet/image/image.py

@@ -585,14 +585,12 @@ def random_size_crop(src, size, area, ratio, interp=2, **kwargs):
         area = (area, 1.0)
     for _ in range(10):
         target_area = random.uniform(area[0], area[1]) * src_area
-        new_ratio = random.uniform(*ratio)
+        log_ratio = (np.log(ratio[0]), np.log(ratio[1]))
+        new_ratio = np.exp(random.uniform(*log_ratio))
 
         new_w = int(round(np.sqrt(target_area * new_ratio)))
         new_h = int(round(np.sqrt(target_area / new_ratio)))
 
-        if random.random() < 0.5:
-            new_h, new_w = new_w, new_h
-
         if new_w <= w and new_h <= h:
             x0 = random.randint(0, w - new_w)
             y0 = random.randint(0, h - new_h)

tests/python/unittest/test_image.py

@@ -355,6 +355,19 @@ def test_det_augmenters(self):
         for batch in det_iter:
             pass
 
+    @with_seed()
+    def test_random_size_crop(self):
+        # test aspect ratio within bounds
+        width = np.random.randint(100, 500)
+        height = np.random.randint(100, 500)
+        src = np.random.rand(height, width, 3) * 255.
+        ratio = (0.75, 1)
+        out, (x0, y0, new_w, new_h) = mx.image.random_size_crop(mx.nd.array(src), size=(width, height), area=0.08, ratio=ratio)
+        _, pts = mx.image.center_crop(mx.nd.array(src), size=(width, height))
+        if (x0, y0, new_w, new_h) != pts:
+            assert ratio[0] <= float(new_w)/new_h <= ratio[1]
+
+
 if __name__ == '__main__':
     import nose
     nose.runmodule()