Add cv2 implementation of image decode

Signed-off-by: GuoRentong <rt.guo@outlook.com>

.gitignore

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README.md

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-# cv2
+## Image Decode Implementation with CV2
+
+*author: Kaiyuan Hu, Rentong Guo*
+
+
+
+### Desription
+
+An image decode operator implementation with OpenCV.
+
+
+
+```python
+import towhee import ops
+
+img_decode = ops.image_decode.cv2()
+img = img_decode('./dog.jpg')
+```
+
+
+
+### Factory method
+
+Create the operator via the following factory method
+
+***ops.image_decode.cv2()***
+
+
+
+### Interface
+
+An image decode operator takes an image path as input. It decodes the image back to ndarray.
+
+
+
+**Parameters:**
+
+​    ***img***: *str*
+
+​    Image file path.
+
+
+
+**Returns**: *numpy.ndarray*
+
+​    The decoded image data.
+
+
+
+### Code Example
+
+Load a image from path './dog.jpg'. 
+
+ *Write the pipeline in simplified style*:
+
+```python
+import towhee.DataCollection as dc
+
+dc.glob(./dog.jpg)
+  .image_decode.cv2()
+  .show()
+```
+
+*Write a same pipeline with explicit inputs/outputs name specifications:*
+
+```python
+import towhee.DataCollection as dc
+
+dc.glob['path'](./dog.jpg)
+  .image_decode.cv2['path', 'img']()
+  .select('img')
+  .show()
+```
 

__init__.py

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+# Copyright 2021 Zilliz. All rights reserved.
+#
+# 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.
+
+from .image_decode_cv2 import ImageDecodeCV2
+
+
+# The factory method
+def cv2():
+    return ImageDecodeCV2()

image_decode_cv2.py

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+# Copyright 2021 Zilliz. All rights reserved.
+#
+# 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.
+
+
+import logging
+import cv2
+import requests
+import numpy as np
+
+from towhee import register
+from towhee.operator import PyOperator, OperatorFlag
+from towhee._types import Image
+
+log = logging.getLogger()
+
+
+@register(output_schema=['img'],
+          flag=OperatorFlag.STATELESS | OperatorFlag.REUSEABLE)
+class ImageDecodeCV2(PyOperator):
+    def __init__(self):
+        pass
+
+    @staticmethod
+    def _load_from_remote(image_url: str) -> np.ndarray:
+        try:
+            r = requests.get(image_url, timeout=(20, 20))
+            if r.status_code // 100 != 2:
+                log.error('Download image from %s failed, error msg: %s, request code: %s ',
+                          image_url, r.text, r.status_code)
+                return None
+            arr = np.asarray(bytearray(r.content), dtype=np.uint8)
+            return cv2.imdecode(arr, -1)
+        except Exception as e:
+            log.error('Download image from %s failed, error msg: %s', image_url, str(e))
+            return False
+
+    @staticmethod
+    def _load_from_local(image_path: str) -> np.ndarray:
+        return cv2.imread(image_path)
+
+    def __call__(self, image_path: str):
+        if image_path.startswith('http'):
+            bgr_cv_image = ImageDecodeCV2._load_from_remote(image_path)
+        else:
+            bgr_cv_image = ImageDecodeCV2._load_from_local(image_path)
+        if bgr_cv_image is None:
+            err = 'Read image %s failed' % image_path
+            log.error(err)
+            raise RuntimeError(err)
+
+        return Image(bgr_cv_image, 'BGR')

requirements.txt

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+opencv-python
+requests
+numpy