diff --git a/README.md b/README.md
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-# swag
+# Image Embedding with SWAG
+
+*author: [Jael Gu](https://github.com/jaelgu*
+
+<br />
+
+## Description
+
+An image embedding operator generates a vector given an image.
+This operator extracts features for image with pretrained [SWAG](https://github.com/facebookresearch/SWAG) models from [Torch Hub](https://pytorch.org/docs/stable/hub.html).
+SWAG implements models from the paper [Revisiting Weakly Supervised Pre-Training of Visual Perception Models](https://arxiv.org/abs/2201.08371).
+To achieve higher accuracy in image classification, SWAG uses hashtags to perform weakly supervised learning instead of fully supervised pretraining with image class labels.
+
+<br />
+
+## Code Example
+
+Load an image from path './towhee.jpg'
+and use the pretrained SWAG model 'vit_b16_in1k' to generate an image embedding. 
+
+ *Write the pipeline in simplified style:*
+
+```python
+import towhee
+
+(
+    towhee.glob('./towhee.jpg')
+          .image_decode()
+          .image_embedding.swag(model_name='vit_b16_in1k')
+          .show()
+)
+```
+<img src="./result1.png" width="800px"/>
+
+*Write a same pipeline with explicit inputs/outputs name specifications:*
+
+```python
+import towhee
+
+(
+    towhee.glob['path']('./towhee.jpg')
+          .image_decode['path', 'img']()
+          .image_embedding.swag['img', 'vec'](model_name='vit_b16_in1k')
+          .select['img', 'vec']()
+          .show()
+)
+```
+<img src="./result2.png" width="800px"/>
+
+<br />
+
+## Factory Constructor
+
+Create the operator via the following factory method
+
+***image_embedding.swag(model_name='vit_b16_in1k', skip_preprocess=False)***
+
+**Parameters:**
+
+***model_name:*** *str*
+
+The model name in string. The default value is "vit_b16_in1k".
+Supported model names:
+- vit_b16_in1k
+- vit_l16_in1k 
+- vit_h14_in1k
+- regnety_16gf_in1k
+- regnety_32gf_in1k
+- regnety_128gf_in1k
+
+***skip_preprocess:*** *bool*
+
+The flag to control whether to skip image preprocess.
+The default value is False.
+If set to True, it will skip image preprocessing steps (transforms).
+In this case, input image data must be prepared in advance in order to properly fit the model.
+
+<br />
+
+## Interface
+
+An image embedding operator takes a towhee image as input.
+It uses the pre-trained model specified by model name to generate an image embedding in ndarray.
+
+**Parameters:**
+
+***img:*** *towhee.types.Image (a sub-class of numpy.ndarray)*
+
+The decoded image data in numpy.ndarray.
+
+
+
+**Returns:** *numpy.ndarray*
+
+The image embedding extracted by model.
+
+
 
diff --git a/__init__.py b/__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 .swag import Swag
+
+
+def swag(**kwargs):
+    return Swag(**kwargs)
diff --git a/requirements.txt b/requirements.txt
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+++ b/requirements.txt
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+numpy
+pillow
+towhee>=0.6.1
+torch>=1.8.0
+torchvision>=0.9.0
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diff --git a/swag.py b/swag.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 numpy
+import os
+from pathlib import Path
+
+import towhee
+from towhee.operator.base import NNOperator, OperatorFlag
+from towhee.types.arg import arg, to_image_color
+from towhee import register
+
+import torch
+from torch import nn
+from torchvision import transforms
+
+from PIL import Image as PILImage
+
+import warnings
+
+warnings.filterwarnings('ignore')
+log = logging.getLogger()
+
+
+@register(output_schema=['vec'])
+class Swag(NNOperator):
+    """
+    Pytorch image embedding operator that uses the Pytorch Image Model (timm) collection.
+    Args:
+        model_name (`str`):
+            Which model to use for the embeddings.
+        skip_preprocess (`bool = False`):
+            Whether skip image transforms.
+    """
+
+    def __init__(self, model_name: str, skip_preprocess: bool = False) -> None:
+        super().__init__()
+        self.device = 'cuda' if torch.cuda.is_available() else 'cpu'
+
+        self.skip_tfms = skip_preprocess
+        self.tfms = self.get_transforms(model_name)
+
+        self.model_name = model_name
+        self.model = torch.hub.load("facebookresearch/swag", model=model_name)
+        self.model.to(self.device)
+        self.model.eval()
+        self.extract_features = FeatureExtractor(self.model)
+
+    @arg(1, to_image_color('RGB'))
+    def __call__(self, img: towhee._types.Image) -> numpy.ndarray:
+        img = PILImage.fromarray(img.astype('uint8'), 'RGB')
+        if not self.skip_tfms:
+            img = self.tfms(img).unsqueeze(0)
+        img = img.to(self.device)
+        features, _ = self.extract_features(img)
+        if features.dim() == 4:
+            global_pool = nn.AdaptiveAvgPool2d(1)
+            features = global_pool(features)
+
+        features = features.to('cpu')
+        vec = features.flatten().detach().numpy()
+        return vec
+
+    def save_model(self, format: str = 'pytorch', path: str = 'default'):
+        if path == 'default':
+            path = str(Path(__file__).parent)
+            name = self.model_name.replace('/', '-')
+            path = os.path.join(path, name)
+        inputs = torch.ones(1, 3, 224, 224)
+        if format == 'pytorch':
+            torch.save(self.model, path)
+        elif format == 'torchscript':
+            path = path + '.pt'
+            try:
+                try:
+                    jit_model = torch.jit.script(self.model)
+                except Exception:
+                    jit_model = torch.jit.trace(self.model, inputs, strict=False)
+                torch.jit.save(jit_model, path)
+            except Exception as e:
+                log.error(f'Fail to save as torchscript: {e}.')
+                raise RuntimeError(f'Fail to save as torchscript: {e}.')
+        elif format == 'onxx':
+            pass  # todo
+        else:
+            log.error(f'Save model: unsupported format "{format}".')
+
+    @staticmethod
+    def supported_model_names(format: str = None):
+        full_list = [
+            'vit_h14_in1k',
+            'vit_l16_in1k',
+            'vit_b16_in1k',
+            'regnety_16gf_in1k',
+            'regnety_32gf_in1k',
+            'regnety_128gf_in1k',
+            ]
+        full_list.sort()
+        if format is None:
+            model_list = full_list
+        elif format == 'pytorch':
+            to_remove = []
+            assert set(to_remove).issubset(set(full_list))
+            model_list = list(set(full_list) - set(to_remove))
+        else:  # todo: format in {'torchscript', 'onnx', 'tensorrt'}
+            log.error(f'Invalid format "{format}". Currently supported formats: "pytorch".')
+        return model_list
+
+    @staticmethod
+    def get_transforms(model_name):
+        model_resolution = {
+            'vit_h14_in1k': 518,
+            'vit_l16_in1k': 512,
+            'vit_b16_in1k': 384,
+            'regnety_16gf_in1k': 384,
+            'regnety_32gf_in1k': 384,
+            'regnety_128gf_in1k': 384
+        }
+        if model_name not in model_resolution.keys():
+            log.warning('No transforms specified for model "%s", using resolution 384.', model_name)
+            resolution = 384
+        else:
+            resolution = model_resolution[model_name]
+        transform = transforms.Compose([
+            transforms.Resize(
+                resolution,
+                interpolation=transforms.InterpolationMode.BICUBIC,
+            ),
+            transforms.CenterCrop(resolution),
+            transforms.ToTensor(),
+            transforms.Normalize(
+                mean=[0.485, 0.456, 0.406], std=[0.229, 0.224, 0.225]
+            ),
+        ])
+        return transform
+
+
+class FeatureExtractor(nn.Module):
+    def __init__(self, model: nn.Module):
+        super().__init__()
+        self.model = model
+        self.features = None
+
+        for name, child in self.model.named_children():
+            if name == 'trunk_output':
+                self.handler = child.register_forward_hook(self.save_outputs_hook())
+
+    def save_outputs_hook(self):
+        def fn(_, __, output):
+            self.features = output
+        return fn
+
+    def forward(self, x):
+        outs = self.model(x)
+        self.handler.remove()
+        return self.features, outs
+
+
+if __name__ == '__main__':
+    from towhee import ops
+
+    path = '/Users/mengjiagu/Desktop/models/data/image/animals10/bird.jpg'
+
+    decoder = ops.image_decode.cv2()
+    img = decoder(path)
+    op = Swag('vit_b16_in1k')
+    # op = Swag('regnety_16gf_in1k')
+    out = op(img)
+    print(out.shape)