add md and py

tutorials/style-transfer/README.md

+# 图像风格迁移
+
+
+图像的风格迁移是卷积神经网络有趣的应用之一。那什么是风格迁移呢？下图第一列左边的图为相机拍摄的一张普通图片，右边的图为梵高的名画星空。那如何让左边的普通图片拥有星空的风格呢。神经网络的风格迁移就可以帮助你生成第二列的这样的图片。
+
+
+<div align=center>
+ <img src="images/markdown/img1.png" width = "600" height = "300"  />
+</br>
+ <img src="images/markdown/img2.png" width = "300" height = "300"  divalign=center />
+
+<div align=left>
+
+## 基本原理
+风格迁移的目标就是使得生成图片的内容与内容图片（content image）尽可能相似。由于在计算机中，我们用一个一个像素点表示图片，所以两个图片的相似程度我们可以用每个像素点的欧式距离来表示。而两个图片的风格相似度，我们采用两个图片在卷积神经网络中相同的一层特征图的gram矩阵的欧式距离来表示。对于一个特征图gram矩阵的计算如下所示：
+
+```python
+# tensor shape is [1, c, h, w]
+_, c, h, w = tensor.shape
+tensor = fluid.layers.reshape(c, h * w)
+# gram matrix with shape: [c, c]
+gram_matrix = fluid.layers.matmul(tensor, fluid.layers.transpose(tensor, [1, 0]))
+```
+
+最终风格迁移的问题转化为优化上述的两个欧式距离的问题。这里要注意的是，我们使用一个在imagenet上预训练好的模型vgg16，并且固定参数，优化器只更新输入的生成图像的值。
+
+## 风格迁移
+执行如下命令，就可以进行风格迁移。生成的图像会保存在```--save-dir```中。
+```python
+python -u style-transfer.py --content-image /path/to/your-content-image --style-image /path/to/your-content-image --save-dir /path/to/your-output-dir
+```
+
+具体的生成过程也可以参考[style-transfer.ipynb](./hapi-style-transfer.ipynb)
+
+
+## 参考文献
+
+[A Neural Algorithm of Artistic Style](https://arxiv.org/abs/1508.06576)

tutorials/style-transfer/style-transfer.py

+import os
+import argparse
+import numpy as np
+import matplotlib.pyplot as plt
+
+from hapi.model import Model, Loss
+
+from hapi.vision.models import vgg16
+from hapi.vision.transform import transforms
+from paddle import fluid
+from paddle.fluid.io import Dataset
+
+import cv2
+import copy
+
+
+def load_image(image_path, max_size=400, shape=None):
+    image = cv2.imread(image_path)
+    image = image.astype('float32') / 255.0
+    size = shape if shape is not None else max_size if max(
+        image.shape[:2]) > max_size else max(image.shape[:2])
+
+    transform = transforms.Compose([
+        transforms.Resize(size), transforms.Permute(),
+        transforms.Normalize([0.485, 0.456, 0.406], [0.229, 0.224, 0.225])
+    ])
+    image = transform(image)[np.newaxis, :3, :, :]
+    image = fluid.dygraph.to_variable(image)
+    return image
+
+
+def image_restore(image):
+    image = np.squeeze(image.numpy(), 0)
+    image = image.transpose(1, 2, 0)
+    image = image * np.array((0.229, 0.224, 0.225)) + np.array(
+        (0.485, 0.456, 0.406))
+
+    image = image.clip(0, 1)
+    return image
+
+
+class StyleTransferModel(Model):
+    def __init__(self):
+        super(StyleTransferModel, self).__init__()
+        # pretrained设置为true，会自动下载imagenet上的预训练权重并加载
+        vgg = vgg16(pretrained=True)
+        self.base_model = vgg.features
+        for p in self.base_model.parameters():
+            p.stop_gradient = True
+        self.layers = {
+            '0': 'conv1_1',
+            '3': 'conv2_1',
+            '6': 'conv3_1',
+            '10': 'conv4_1',
+            '11': 'conv4_2',  ## content representation
+            '14': 'conv5_1'
+        }
+
+    def forward(self, image):
+        outputs = []
+        for name, layer in self.base_model.named_sublayers():
+            image = layer(image)
+            if name in self.layers:
+                outputs.append(image)
+        return outputs
+
+
+class StyleTransferLoss(Loss):
+    def __init__(self,
+                 content_loss_weight=1,
+                 style_loss_weight=1e5,
+                 style_weights=[1.0, 0.8, 0.5, 0.3, 0.1]):
+        super(StyleTransferLoss, self).__init__()
+        self.content_loss_weight = content_loss_weight
+        self.style_loss_weight = style_loss_weight
+        self.style_weights = style_weights
+
+    def forward(self, outputs, labels):
+        content_features = labels[-1]
+        style_features = labels[:-1]
+
+        # 计算图像内容相似度的loss
+        content_loss = fluid.layers.mean((outputs[-2] - content_features)**2)
+
+        # 计算风格相似度的loss
+        style_loss = 0
+        style_grams = [self.gram_matrix(feat) for feat in style_features]
+        style_weights = self.style_weights
+        for i, weight in enumerate(style_weights):
+            target_gram = self.gram_matrix(outputs[i])
+            layer_loss = weight * fluid.layers.mean((target_gram - style_grams[
+                i])**2)
+            b, d, h, w = outputs[i].shape
+            style_loss += layer_loss / (d * h * w)
+
+        total_loss = self.content_loss_weight * content_loss + self.style_loss_weight * style_loss
+        return total_loss
+
+    def gram_matrix(self, A):
+        if len(A.shape) == 4:
+            _, c, h, w = A.shape
+            A = fluid.layers.reshape(A, (c, h * w))
+        GA = fluid.layers.matmul(A, fluid.layers.transpose(A, [1, 0]))
+
+        return GA
+
+
+def main():
+    # 启动动态图模式
+    fluid.enable_dygraph()
+
+    content = load_image(FLAGS.content_image)
+    style = load_image(FLAGS.style_image, shape=tuple(content.shape[-2:]))
+
+    model = StyleTransferModel()
+    style_loss = StyleTransferLoss()
+
+    # 使用内容图像初始化要生成的图像
+    target = Model.create_parameter(model, shape=content.shape)
+    target.set_value(content.numpy())
+
+    optimizer = fluid.optimizer.Adam(
+        parameter_list=[target], learning_rate=FLAGS.lr)
+    model.prepare(optimizer, style_loss)
+
+    content_fetures = model.test(content)
+    style_features = model.test(style)
+
+    # 将两个特征组合，作为损失函数的label传给模型
+    feats = style_features + [content_fetures[-2]]
+
+    # 训练5000个step，每500个step画一下生成的图像查看效果
+    steps = FLAGS.steps
+    for i in range(steps):
+        outs = model.train(target, feats)
+        if i % 500 == 0:
+            print('iters:', i, 'loss:', outs[0][0])
+
+    if not os.path.exists(FLAGS.save_dir):
+        os.makedirs(FLAGS.save_dir)
+
+    # 保存生成好的图像
+    name = FLAGS.content_image.split(os.sep)[-1]
+    output_path = os.path.join(FLAGS.save_dir, 'generated_' + name)
+    cv2.imwrite(output_path,
+                cv2.cvtColor((image_restore(target) * 255).astype('uint8'),
+                             cv2.COLOR_RGB2BGR))
+
+
+if __name__ == '__main__':
+    parser = argparse.ArgumentParser("Resnet Training on ImageNet")
+    parser.add_argument(
+        "--content-image",
+        type=str,
+        default='./images/chicago_cropped.jpg',
+        help="content image")
+    parser.add_argument(
+        "--style-image",
+        type=str,
+        default='./images/Starry-Night-by-Vincent-Van-Gogh-painting.jpg',
+        help="style image")
+    parser.add_argument(
+        "--save-dir", type=str, default='./output', help="output dir")
+    parser.add_argument(
+        "--steps", default=5000, type=int, help="number of steps to run")
+    parser.add_argument(
+        '--lr',
+        '--learning-rate',
+        default=1e-3,
+        type=float,
+        metavar='LR',
+        help='initial learning rate')
+    FLAGS = parser.parse_args()
+    main()