train_imagenet.py 文件源码

def get_example(self, i):
        # It reads the i-th image/label pair and return a preprocessed image.
        # It applies following preprocesses:
        #     - Cropping (random or center rectangular)
        #     - Random flip
        #     - Scaling to [0, 1] value
        crop_size = self.crop_size

        image, label = self.base[i]
        _, h, w = image.shape

        if self.random:
            # Randomly crop a region and flip the image
            top = random.randint(0, h - crop_size - 1)
            left = random.randint(0, w - crop_size - 1)
            if random.randint(0, 1):
                image = image[:, :, ::-1]
        else:
            # Crop the center
            top = (h - crop_size) // 2
            left = (w - crop_size) // 2
        bottom = top + crop_size
        right = left + crop_size

        image = image[:, top:bottom, left:right]
        image -= self.mean[:, top:bottom, left:right]
        image *= (1.0 / 255.0)  # Scale to [0, 1]
        return image, label


# chainermn.create_multi_node_evaluator can be also used with user customized
# evaluator classes that inherit chainer.training.extensions.Evaluator.