TensorFlow 实战（五）—— 图像预处理

当然 tensorflow 并不是一种用于图像处理的框架，这里图像处理仅仅是一些简单的像素级操作，最终目的比如用于数据增强；

• tf.random_crop()
• tf.image.random_flip_left_right()：
• tf.image.random_hue()
  
  • random_contrast()
  • random_brightness()
  • random_saturation()

def pre_process_image(image, training):
    # This function takes a single image as input,
    # and a boolean whether to build the training or testing graph.

    if training:
        # For training, add the following to the TensorFlow graph.

        # Randomly crop the input image.
        image = tf.random_crop(image, size=[img_size_cropped, img_size_cropped, num_channels])

        # Randomly flip the image horizontally.
        image = tf.image.random_flip_left_right(image)

        # Randomly adjust hue, contrast and saturation.
        image = tf.image.random_hue(image, max_delta=0.05)
        image = tf.image.random_contrast(image, lower=0.3, upper=1.0)
        image = tf.image.random_brightness(image, max_delta=0.2)
        image = tf.image.random_saturation(image, lower=0.0, upper=2.0)

        # Some of these functions may overflow and result in pixel
        # values beyond the [0, 1] range. It is unclear from the
        # documentation of TensorFlow 0.10.0rc0 whether this is
        # intended. A simple solution is to limit the range.

        # Limit the image pixels between [0, 1] in case of overflow.
        image = tf.minimum(image, 1.0)
        image = tf.maximum(image, 0.0)
    else:
        # For training, add the following to the TensorFlow graph.

        # Crop the input image around the centre so it is the same
        # size as images that are randomly cropped during training.
        image = tf.image.resize_image_with_crop_or_pad(image,
                                                       target_height=img_size_cropped,
                                                       target_width=img_size_cropped)

    return image