Added PyTorch to TensorFlow model conversion

Author: Anastasia

PyTorch-to-TensorFlow-Model-Conversion/FullyConvolutionalResnet18.py

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+import cv2
+import numpy as np
+import tensorflow as tf
+import torch
+from albumentations import (
+    Compose,
+    Normalize,
+)
+from pytorch2keras.converter import pytorch_to_keras
+from torch.autograd import Variable
+
+from PyTorchFullyConvolutionalResnet18 import FullyConvolutionalResnet18
+
+
+def converted_fully_convolutional_resnet18(
+    input_tensor, pretrained_resnet=True,
+):
+    # define input tensor
+    input_var = Variable(torch.FloatTensor(input_tensor))
+
+    # get PyTorch ResNet18 model
+    model_to_transfer = FullyConvolutionalResnet18(pretrained=pretrained_resnet)
+    model_to_transfer.eval()
+
+    # convert PyTorch model to Keras
+    model = pytorch_to_keras(
+        model_to_transfer,
+        input_var,
+        [input_var.shape[-3:]],
+        change_ordering=True,
+        verbose=False,
+        name_policy="keep",
+    )
+
+    return model
+
+
+if __name__ == "__main__":
+    # read ImageNet class ids to a list of labels
+    with open("imagenet_classes.txt") as f:
+        labels = [line.strip() for line in f.readlines()]
+
+    # read image
+    original_image = cv2.imread("camel.jpg")
+
+    # convert original image to RGB format
+    image = cv2.cvtColor(original_image, cv2.COLOR_BGR2RGB)
+
+    # transform input image:
+    transform = Compose(
+        [
+            Normalize(
+                # subtract mean
+                mean=(0.485, 0.456, 0.406),
+                # divide by standard deviation
+                std=(0.229, 0.224, 0.225),
+            ),
+        ],
+    )
+    # apply image transformations, (725, 1920, 3)
+    image = transform(image=image)["image"]
+
+    # NHWC: (1, 725, 1920, 3)
+    predict_image = tf.expand_dims(image, 0)
+    # NCHW: (1, 3, 725, 1920)
+    image = np.transpose(tf.expand_dims(image, 0).numpy(), [0, 3, 1, 2])
+
+    # get transferred torch ResNet18 with pre-trained ImageNet weights
+    model = converted_fully_convolutional_resnet18(
+        input_tensor=image, pretrained_resnet=True,
+    )
+
+    # Perform inference.
+    # Instead of a 1×1000 vector, we will get a
+    # 1×1000×n×m output ( i.e. a probability map
+    # of size n × m for each 1000 class,
+    # where n and m depend on the size of the image).
+    preds = model.predict(predict_image)
+    # NHWC: (1, 3, 8, 1000) back to NCHW: (1, 1000, 3, 8)
+    preds = tf.transpose(preds, (0, 3, 1, 2))
+    preds = tf.nn.softmax(preds, axis=1)
+    print("Response map shape : ", preds.shape)
+
+    # find the class with the maximum score in the n x m output map
+    pred = tf.math.reduce_max(preds, axis=1)
+    class_idx = tf.math.argmax(preds, axis=1)
+
+    row_max = tf.math.reduce_max(pred, axis=1)
+    row_idx = tf.math.argmax(pred, axis=1)
+
+    col_idx = tf.math.argmax(row_max, axis=1)
+
+    predicted_class = tf.gather_nd(
+        class_idx, (0, tf.gather_nd(row_idx, (0, col_idx[0])), col_idx[0]),
+    )
+
+    # print top predicted class
+    print("Predicted Class : ", labels[predicted_class], predicted_class)
+
+    # find the n × m score map for the predicted class
+    score_map = tf.expand_dims(preds[0, predicted_class, :, :], 0).numpy()
+    score_map = score_map[0]
+
+    # resize score map to the original image size
+    score_map = cv2.resize(
+        score_map, (original_image.shape[1], original_image.shape[0]),
+    )
+
+    # binarize score map
+    _, score_map_for_contours = cv2.threshold(
+        score_map, 0.25, 1, type=cv2.THRESH_BINARY,
+    )
+
+    score_map_for_contours = score_map_for_contours.astype(np.uint8).copy()
+
+    # Find the contour of the binary blob
+    contours, _ = cv2.findContours(
+        score_map_for_contours, mode=cv2.RETR_EXTERNAL, method=cv2.CHAIN_APPROX_SIMPLE,
+    )
+
+    # find bounding box around the object.
+    rect = cv2.boundingRect(contours[0])
+
+    # apply score map as a mask to original image
+    score_map = score_map - np.min(score_map[:])
+    score_map = score_map / np.max(score_map[:])
+
+    score_map = cv2.cvtColor(score_map, cv2.COLOR_GRAY2BGR)
+    masked_image = (original_image * score_map).astype(np.uint8)
+
+    # display bounding box
+    cv2.rectangle(
+        masked_image, rect[:2], (rect[0] + rect[2], rect[1] + rect[3]), (0, 0, 255), 2,
+    )
+
+    # display images
+    cv2.imshow("Original Image", original_image)
+    cv2.imshow("scaled_score_map", score_map)
+    cv2.imshow("activations_and_bbox", masked_image)
+    cv2.waitKey(0)

PyTorch-to-TensorFlow-Model-Conversion/PyTorchFullyConvolutionalResnet18.py

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+import torch
+import torch.nn as nn
+from torch.hub import load_state_dict_from_url
+from torchvision import models
+
+
+# Define the architecture by modifying resnet.
+# Original code is here
+# https://github.com/pytorch/vision/blob/b2e95657cd5f389e3973212ba7ddbdcc751a7878/torchvision/models/resnet.py
+class FullyConvolutionalResnet18(models.ResNet):
+    def __init__(self, num_classes=1000, pretrained=False, **kwargs):
+
+        # Start with standard resnet18 defined here
+        # https://github.com/pytorch/vision/blob/b2e95657cd5f389e3973212ba7ddbdcc751a7878/torchvision/models/resnet.py
+        super().__init__(
+            block=models.resnet.BasicBlock,
+            layers=[2, 2, 2, 2],
+            num_classes=num_classes,
+            **kwargs,
+        )
+        if pretrained:
+            state_dict = load_state_dict_from_url(
+                models.resnet.model_urls["resnet18"], progress=True,
+            )
+            self.load_state_dict(state_dict)
+
+        # Replace AdaptiveAvgPool2d with standard AvgPool2d
+        # https://github.com/pytorch/vision/blob/b2e95657cd5f389e3973212ba7ddbdcc751a7878/torchvision/models/resnet.py#L153-L154
+        self.avgpool = nn.AvgPool2d((7, 7))
+
+        # Add final Convolution Layer.
+        self.last_conv = torch.nn.Conv2d(
+            in_channels=self.fc.in_features, out_channels=num_classes, kernel_size=1,
+        )
+        self.last_conv.weight.data.copy_(
+            self.fc.weight.data.view(*self.fc.weight.data.shape, 1, 1),
+        )
+        self.last_conv.bias.data.copy_(self.fc.bias.data)
+
+    # Reimplementing forward pass.
+    # Replacing the following code
+    # https://github.com/pytorch/vision/blob/b2e95657cd5f389e3973212ba7ddbdcc751a7878/torchvision/models/resnet.py#L197-L213
+    def _forward_impl(self, x):
+        # Standard forward for resnet18
+        x = self.conv1(x)
+        x = self.bn1(x)
+        x = self.relu(x)
+        x = self.maxpool(x)
+
+        x = self.layer1(x)
+        x = self.layer2(x)
+        x = self.layer3(x)
+        x = self.layer4(x)
+        x = self.avgpool(x)
+
+        # Notice, there is no forward pass
+        # through the original fully connected layer.
+        # Instead, we forward pass through the last conv layer
+        x = self.last_conv(x)
+        return x

PyTorch-to-TensorFlow-Model-Conversion/README.md

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+This contains the code for **PyTorch to Tensorflow Model Conversion**. For more information - visit
+[**PyTorch to Tensorflow Model Conversion**](https://www.learnopencv.com/pytorch-to-tensorflow-model-conversion/)
+
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