[MXNET-411] Add ROI Align

CONTRIBUTORS.md

@@ -170,4 +170,4 @@ List of Contributors
 * [Sina Afrooze](https://github.com/safrooze)
 * [Sergey Sokolov](https://github.com/Ishitori)
 * [Thomas Delteil](https://github.com/ThomasDelteil)
-
+* [Hang Zhang](http://hangzh.com)

docs/api/python/ndarray/contrib.md

@@ -45,6 +45,7 @@ In the rest of this document, we list routines provided by the `ndarray.contrib`
     MultiProposal
     PSROIPooling
     Proposal
+    ROIAlign
     count_sketch
     ctc_loss
     dequantize

docs/api/python/symbol/contrib.md

@@ -45,6 +45,7 @@ In the rest of this document, we list routines provided by the `symbol.contrib`
     MultiProposal
     PSROIPooling
     Proposal
+    ROIAlign
     count_sketch
     ctc_loss
     dequantize

src/operator/contrib/roi_align-inl.h

@@ -0,0 +1,63 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+/*!
+ * Copyright (c) 2018 by Contributors
+ * \file roi_align-inl.h
+ * \brief roi align operator and symbol
+ * \author Hang Zhang
+ * modified from Caffe2
+*/
+#ifndef MXNET_OPERATOR_CONTRIB_ROI_ALIGN_INL_H_
+#define MXNET_OPERATOR_CONTRIB_ROI_ALIGN_INL_H_
+
+#include <vector>
+#include <utility>
+#include "../mshadow_op.h"
+#include "../tensor/init_op.h"
+
+
+namespace mxnet {
+namespace op {
+
+
+// Declare enumeration of input order to make code more intuitive.
+// These enums are only visible within this header
+namespace roialign {
+enum ROIAlignOpInputs {kData, kBox};
+enum ROIAlignOpOutputs {kOut};
+}  // roialign
+
+
+struct ROIAlignParam : public dmlc::Parameter<ROIAlignParam> {
+  TShape pooled_size;
+  float spatial_scale;
+  DMLC_DECLARE_PARAMETER(ROIAlignParam) {
+    DMLC_DECLARE_FIELD(pooled_size)
+    .set_expect_ndim(2).enforce_nonzero()
+    .describe("ROI Align output roi feature map height and width: (h, w)");
+    DMLC_DECLARE_FIELD(spatial_scale).set_range(0.0, 1.0)
+    .describe("Ratio of input feature map height (or w) to raw image height (or w). "
+    "Equals the reciprocal of total stride in convolutional layers");
+  }
+};
+
+}  // namespace op
+}  // namespace mxnet
+
+#endif  // MXNET_OPERATOR_CONTRIB_ROI_ALIGN_INL_H_