!2165 Add image.CentralCrop.

Merge pull request !2165 from liuxiao/central_crop

mindspore/nn/layer/image.py

@@ -23,7 +23,7 @@ from mindspore._checkparam import Validator as validator
 from mindspore._checkparam import Rel
 from ..cell import Cell
 
-__all__ = ['ImageGradients', 'SSIM', 'PSNR']
+__all__ = ['ImageGradients', 'SSIM', 'PSNR', 'CentralCrop']
 
 class ImageGradients(Cell):
     r"""
@@ -259,3 +259,71 @@ class PSNR(Cell):
         psnr = 10 * P.Log()(F.square(max_val) / mse) / F.scalar_log(10.0)
 
         return psnr
+
+
+@constexpr
+def _check_input_3d_or_4d(input_shape, param_name, func_name):
+    """check input 3d or 4d"""
+    if len(input_shape) != 3 and len(input_shape) != 4:
+        raise ValueError(f"{func_name} {param_name} should be 3d or 4d, but got shape {input_shape}")
+    return True
+
+@constexpr
+def _get_bbox(rank, shape, central_fraction):
+    """get bbox start and size for slice"""
+    if rank == 3:
+        c, h, w = shape
+    else:
+        n, c, h, w = shape
+
+    bbox_h_start = int((float(h) - float(h) * central_fraction) / 2)
+    bbox_w_start = int((float(w) - float(w) * central_fraction) / 2)
+    bbox_h_size = h - bbox_h_start * 2
+    bbox_w_size = w - bbox_w_start * 2
+
+    if rank == 3:
+        bbox_begin = (0, bbox_h_start, bbox_w_start)
+        bbox_size = (c, bbox_h_size, bbox_w_size)
+    else:
+        bbox_begin = (0, 0, bbox_h_start, bbox_w_start)
+        bbox_size = (n, c, bbox_h_size, bbox_w_size)
+
+    return bbox_begin, bbox_size
+
+class CentralCrop(Cell):
+    """
+    Crop the centeral region of the images with the central_fraction.
+
+    Args:
+        central_fraction (float): Fraction of size to crop. It must be float and in range (0.0, 1.0].
+
+    Inputs:
+        - **image** (Tensor) - A 3-D tensor of shape [C, H, W], or a 4-D tensor of shape [N, C, H, W].
+
+    Outputs:
+        Tensor, 3-D or 4-D float tensor, according to the input.
+
+    Examples:
+        >>> net = nn.CentralCrop(central_fraction=0.5)
+        >>> image = Tensor(np.random.random((4, 3, 4, 4)), mindspore.float32)
+        >>> output = net(image)
+    """
+
+    def __init__(self, central_fraction):
+        super(CentralCrop, self).__init__()
+        validator.check_value_type("central_fraction", central_fraction, [float], self.cls_name)
+        self.central_fraction = validator.check_number_range('central_fraction', central_fraction,
+                                                             0.0, 1.0, Rel.INC_RIGHT, self.cls_name)
+        self.slice = P.Slice()
+
+    def construct(self, image):
+        image_shape = F.shape(image)
+        rank = len(image_shape)
+        _check_input_3d_or_4d(image_shape, "image", self.cls_name)
+        if self.central_fraction == 1.0:
+            return image
+
+        bbox_begin, bbox_size = _get_bbox(rank, image_shape, self.central_fraction)
+        image = self.slice(image, bbox_begin, bbox_size)
+
+        return image

tests/ut/python/nn/test_central_crop.py

+# Copyright 2020 Huawei Technologies Co., Ltd
+#
+# Licensed 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.
+# ============================================================================
+"""
+test CentralCrop
+"""
+import numpy as np
+import pytest
+
+import mindspore.nn as nn
+from mindspore import Tensor
+from mindspore.common import dtype as mstype
+from mindspore.common.api import _executor
+
+
+class CentralCropNet(nn.Cell):
+    def __init__(self, central_fraction):
+        super(CentralCropNet, self).__init__()
+        self.net = nn.CentralCrop(central_fraction)
+
+    def construct(self, image):
+        return self.net(image)
+
+
+def test_compile_3d_central_crop():
+    central_fraction = 0.2
+    net = CentralCropNet(central_fraction)
+    image = Tensor(np.random.random((3, 16, 16)), mstype.float32)
+    _executor.compile(net, image)
+
+
+def test_compile_4d_central_crop():
+    central_fraction = 0.5
+    net = CentralCropNet(central_fraction)
+    image = Tensor(np.random.random((8, 3, 16, 16)), mstype.float32)
+    _executor.compile(net, image)
+
+
+def test_central_fraction_bool():
+    central_fraction = True
+    with pytest.raises(TypeError):
+        _ = CentralCropNet(central_fraction)
+
+
+def test_central_crop_central_fraction_negative():
+    central_fraction = -1.0
+    with pytest.raises(ValueError):
+        _ = CentralCropNet(central_fraction)
+
+
+def test_central_fraction_zero():
+    central_fraction = 0.0
+    with pytest.raises(ValueError):
+        _ = CentralCropNet(central_fraction)
+
+
+def test_central_crop_invalid_5d_input():
+    invalid_shape = (8, 3, 16, 16, 1)
+    invalid_image = Tensor(np.random.random(invalid_shape))
+
+    net = CentralCropNet(central_fraction=0.5)
+    with pytest.raises(ValueError):
+        _executor.compile(net, invalid_image)