Make center_crop_and_resize support non-quadratics

Make the function center_crop_and_resize() support non-quadratic
output shapes and crop padding shapes. The arguments image_size and
crop_padding should be able to either be scalars (like they currently
are) or lists or tuples containing both a height and a width.

Author: krikru

efficientnet/preprocessing.py

@@ -27,21 +27,37 @@ def center_crop_and_resize(image, image_size, crop_padding=32, interpolation="bi
     assert image.ndim in {2, 3}
     assert interpolation in MAP_INTERPOLATION_TO_ORDER.keys()
 
-    h, w = image.shape[:2]
+    in_h, in_w = image.shape[:2]
 
-    padded_center_crop_size = int(
-        (image_size / (image_size + crop_padding)) * min(h, w)
-    )
-    offset_height = ((h - padded_center_crop_size) + 1) // 2
-    offset_width = ((w - padded_center_crop_size) + 1) // 2
+    if isinstance(image_size, (int, float)):
+        out_h = out_w = image_size
+    else:
+        out_h, out_w = image_size
+
+    if isinstance(crop_padding, (int, float)):
+        crop_padding_h = crop_padding_w = crop_padding
+    else:
+        crop_padding_h, crop_padding_w = crop_padding
+
+    padded_center_crop_shape_post_scaling = (out_h + crop_padding_h,
+                                             out_w + crop_padding_w)
+
+    inv_scale = min(in_h / padded_center_crop_shape_post_scaling[0],
+                in_w / padded_center_crop_shape_post_scaling[1])
+
+    unpadded_center_crop_size_pre_scaling = (round(out_h * inv_scale),
+                                             round(out_w * inv_scale))
+
+    offset_h = ((in_h - unpadded_center_crop_size_pre_scaling[0]) + 1) // 2
+    offset_w = ((in_w - unpadded_center_crop_size_pre_scaling[1]) + 1) // 2
 
     image_crop = image[
-                 offset_height: padded_center_crop_size + offset_height,
-                 offset_width: padded_center_crop_size + offset_width,
+                 offset_h : unpadded_center_crop_size_pre_scaling[0] + offset_h,
+                 offset_w : unpadded_center_crop_size_pre_scaling[1] + offset_w,
                  ]
     resized_image = resize(
         image_crop,
-        (image_size, image_size),
+        (out_h, out_w),
         order=MAP_INTERPOLATION_TO_ORDER[interpolation],
         preserve_range=True,
     )