Allow overriding "regresion weights" used in GenerateProposalsOp

Summary:
Detectron code is inconsistent about when it uses (1, 1, 1, 1) as the
regression weights vs. `cfg.MODEL.BBOX_REG_WEIGHTS` (which has a default
value of (10, 10, 5, 5)). This change allows the caller to make the call
(heh!) about what to use.

Reviewed By: rbgirshick

Differential Revision: D9981875

fbshipit-source-id: 8798408bd2592486eb1a2e40ccb70b9bedfdbf46

detectron/ops/generate_proposals.py

@@ -30,13 +30,17 @@
 class GenerateProposalsOp(object):
     """Output object detection proposals by applying estimated bounding-box
     transformations to a set of regular boxes (called "anchors").
+
+    See comment in utils/boxes:bbox_transform_inv for details abouts the
+    optional `reg_weights` parameter.
     """
 
-    def __init__(self, anchors, spatial_scale, train):
+    def __init__(self, anchors, spatial_scale, train, reg_weights=(1.0, 1.0, 1.0, 1.0)):
         self._anchors = anchors
         self._num_anchors = self._anchors.shape[0]
         self._feat_stride = 1. / spatial_scale
         self._train = train
+        self._reg_weights = reg_weights
 
     def forward(self, inputs, outputs):
         """See modeling.detector.GenerateProposals for inputs/outputs
@@ -144,8 +148,7 @@ def proposals_for_one_image(
         scores = scores[order]
 
         # Transform anchors into proposals via bbox transformations
-        proposals = box_utils.bbox_transform(
-            all_anchors, bbox_deltas, (1.0, 1.0, 1.0, 1.0))
+        proposals = box_utils.bbox_transform(all_anchors, bbox_deltas, self._reg_weights)
 
         # 2. clip proposals to image (may result in proposals with zero area
         # that will be removed in the next step)