Fixed ROI Pooling Output Shape to Consider Multiple ROIs (keras-team#2350) (keras-team#2360)

* Fixed indentation and output shape in roi pooling to consider multiple ROIs

* Formatted code

Author: VarunS1997

keras_cv/layers/object_detection/roi_pool.py

@@ -112,11 +112,12 @@ def _pool_single_sample(self, args):
           feature_map: [H, W, C] float Tensor
           rois: [N, 4] float Tensor
         Returns:
-          pooled_feature_map: [target_size, C] float Tensor
+          pooled_feature_map: [N, target_height, target_width, C] float Tensor
         """
         feature_map, rois = args
         num_rois = rois.get_shape().as_list()[0]
         height, width, channel = feature_map.get_shape().as_list()
+        regions = []
         # TODO (consider vectorize it for better performance)
         for n in range(num_rois):
             # [4]
@@ -127,7 +128,7 @@ def _pool_single_sample(self, args):
             region_width = width * (roi[3] - roi[1])
             h_step = region_height / self.target_height
             w_step = region_width / self.target_width
-            regions = []
+            region_steps = []
             for i in range(self.target_height):
                 for j in range(self.target_width):
                     height_start = y_start + i * h_step
@@ -147,16 +148,18 @@ def _pool_single_sample(self, args):
                         1, width_end - width_start
                     )
                     # [h_step, w_step, C]
-                    region = feature_map[
+                    region_step = feature_map[
                         height_start:height_end, width_start:width_end, :
                     ]
                     # target_height * target_width * [C]
-                    regions.append(tf.reduce_max(region, axis=[0, 1]))
-            regions = tf.reshape(
-                tf.stack(regions),
-                [self.target_height, self.target_width, channel],
+                    region_steps.append(tf.reduce_max(region_step, axis=[0, 1]))
+            regions.append(
+                tf.reshape(
+                    tf.stack(region_steps),
+                    [self.target_height, self.target_width, channel],
+                )
             )
-            return regions
+        return tf.stack(regions)
 
     def get_config(self):
         config = {

keras_cv/layers/object_detection/roi_pool_test.py

@@ -43,7 +43,7 @@ def test_no_quantize(self):
         # | 56, 57, 58, 59(max) | 60, 61, 62, 63(max)   |
         # --------------------------------------------
         expected_feature_map = tf.reshape(
-            tf.constant([27, 31, 59, 63]), [1, 2, 2, 1]
+            tf.constant([27, 31, 59, 63]), [1, 1, 2, 2, 1]
         )
         self.assertAllClose(expected_feature_map, pooled_feature_map)
 
@@ -69,7 +69,7 @@ def test_roi_quantize_y(self):
         # | 56, 57, 58(max)     | 59, 60, 61, 62(max)   | 63 (removed)
         # --------------------------------------------
         expected_feature_map = tf.reshape(
-            tf.constant([26, 30, 58, 62]), [1, 2, 2, 1]
+            tf.constant([26, 30, 58, 62]), [1, 1, 2, 2, 1]
         )
         self.assertAllClose(expected_feature_map, pooled_feature_map)
 
@@ -94,7 +94,7 @@ def test_roi_quantize_x(self):
         # | 48, 49, 50, 51(max) | 52, 53, 54, 55(max)   |
         # --------------------------------------------
         expected_feature_map = tf.reshape(
-            tf.constant([19, 23, 51, 55]), [1, 2, 2, 1]
+            tf.constant([19, 23, 51, 55]), [1, 1, 2, 2, 1]
         )
         self.assertAllClose(expected_feature_map, pooled_feature_map)
 
@@ -121,7 +121,7 @@ def test_roi_quantize_h(self):
         # | 56, 57, 58, 59(max) | 60, 61, 62, 63(max)   |
         # --------------------------------------------
         expected_feature_map = tf.reshape(
-            tf.constant([11, 15, 35, 39, 59, 63]), [1, 3, 2, 1]
+            tf.constant([11, 15, 35, 39, 59, 63]), [1, 1, 3, 2, 1]
         )
         self.assertAllClose(expected_feature_map, pooled_feature_map)
 
@@ -147,7 +147,7 @@ def test_roi_quantize_w(self):
         # | 56, 57(max) | 58, 59, 60(max)   | 61, 62, 63(max)   |
         # --------------------------------------------
         expected_feature_map = tf.reshape(
-            tf.constant([25, 28, 31, 57, 60, 63]), [1, 2, 3, 1]
+            tf.constant([25, 28, 31, 57, 60, 63]), [1, 1, 2, 3, 1]
         )
         self.assertAllClose(expected_feature_map, pooled_feature_map)
 
@@ -168,7 +168,8 @@ def test_roi_feature_map_height_smaller_than_roi(self):
         # ------------------repeated----------------------
         # | 12, 13(max) | 14, 15(max)   |
         expected_feature_map = tf.reshape(
-            tf.constant([1, 3, 1, 3, 5, 7, 9, 11, 9, 11, 13, 15]), [1, 6, 2, 1]
+            tf.constant([1, 3, 1, 3, 5, 7, 9, 11, 9, 11, 13, 15]),
+            [1, 1, 6, 2, 1],
         )
         self.assertAllClose(expected_feature_map, pooled_feature_map)
 
@@ -189,7 +190,7 @@ def test_roi_feature_map_width_smaller_than_roi(self):
         # --------------------------------------------
         expected_feature_map = tf.reshape(
             tf.constant([4, 4, 5, 6, 6, 7, 12, 12, 13, 14, 14, 15]),
-            [1, 2, 6, 1],
+            [1, 1, 2, 6, 1],
         )
         self.assertAllClose(expected_feature_map, pooled_feature_map)
 
@@ -203,10 +204,43 @@ def test_roi_empty(self):
         rois = tf.reshape(tf.constant([0.0, 0.0, 0.0, 0.0]), [1, 1, 4])
         pooled_feature_map = roi_pooler(feature_map, rois)
         # all outputs should be top-left pixel
-        self.assertAllClose(tf.ones([1, 2, 2, 1]), pooled_feature_map)
+        self.assertAllClose(tf.ones([1, 1, 2, 2, 1]), pooled_feature_map)
 
     def test_invalid_image_shape(self):
         with self.assertRaisesRegex(ValueError, "dynamic shape"):
             _ = ROIPooler(
                 "rel_yxyx", target_size=[2, 2], image_shape=[None, 224, 3]
             )
+
+    def test_multiple_rois(self):
+        feature_map = tf.expand_dims(
+            tf.reshape(tf.range(0, 64), [8, 8, 1]), axis=0
+        )
+
+        roi_pooler = ROIPooler(
+            bounding_box_format="yxyx",
+            target_size=[2, 2],
+            image_shape=[224, 224, 3],
+        )
+        rois = tf.constant(
+            [[[0.0, 0.0, 112.0, 112.0], [0.0, 112.0, 224.0, 224.0]]],
+        )
+
+        pooled_feature_map = roi_pooler(feature_map, rois)
+        # the maximum value would be at bottom-right at each block, roi sharded
+        # into 2x2 blocks
+        # | 0, 1, 2, 3          | 4, 5, 6, 7            |
+        # | 8, 9, 10, 11        | 12, 13, 14, 15        |
+        # | 16, 17, 18, 19      | 20, 21, 22, 23        |
+        # | 24, 25, 26, 27(max) | 28, 29, 30, 31(max)   |
+        # --------------------------------------------
+        # | 32, 33, 34, 35      | 36, 37, 38, 39        |
+        # | 40, 41, 42, 43      | 44, 45, 46, 47        |
+        # | 48, 49, 50, 51      | 52, 53, 54, 55        |
+        # | 56, 57, 58, 59(max) | 60, 61, 62, 63(max)   |
+        # --------------------------------------------
+
+        expected_feature_map = tf.reshape(
+            tf.constant([9, 11, 25, 27, 29, 31, 61, 63]), [1, 2, 2, 2, 1]
+        )
+        self.assertAllClose(expected_feature_map, pooled_feature_map)