Module: tf.image
这篇文章主要介绍TensorFlow处理图片这一块，这个模块和之前说过的文件I/O处理一样也是主要从python导过来的。
通过官方文档，我们了解到这个模块主要有一下这些个函数。
Functions
adjust_brightness(...): Adjust the brightness of RGB or Grayscale images.
adjust_contrast(...): Adjust contrast of RGB or grayscale images.
adjust_gamma(...): Performs Gamma Correction on the input image.
adjust_hue(...): Adjust hue of an RGB image.
adjust_saturation(...): Adjust saturation of an RGB image.
central_crop(...): Crop the central region of the image.
convert_image_dtype(...): Convertimagetodtype, scaling its values if needed.
crop_and_resize(...): Extracts crops from the input image tensor and bilinearly resizes them (possibly
crop_to_bounding_box(...): Crops an image to a specified bounding box.
decode_and_crop_jpeg(...): Decode and Crop a JPEG-encoded image to a uint8 tensor.
decode_bmp(...): Decode the first frame of a BMP-encoded image to a uint8 tensor.
decode_gif(...): Decode the first frame of a GIF-encoded image to a uint8 tensor.
decode_image(...): Convenience function fordecode_bmp,decode_gif,decode_jpeg,
decode_jpeg(...): Decode a JPEG-encoded image to a uint8 tensor.
decode_png(...): Decode a PNG-encoded image to a uint8 or uint16 tensor.
draw_bounding_boxes(...): Draw bounding boxes on a batch of images.
encode_jpeg(...): JPEG-encode an image.
encode_png(...): PNG-encode an image.
extract_glimpse(...): Extracts a glimpse from the input tensor.
extract_jpeg_shape(...): Extract the shape information of a JPEG-encoded image.
flip_left_right(...): Flip an image horizontally (left to right).
flip_up_down(...): Flip an image vertically (upside down).
grayscale_to_rgb(...): Converts one or more images from Grayscale to RGB.
hsv_to_rgb(...): Convert one or more images from HSV to RGB.
image_gradients(...): Returns image gradients (dy, dx) for each color channel.
is_jpeg(...): Convenience function to check if the 'contents' encodes a JPEG image.
non_max_suppression(...): Greedily selects a subset of bounding boxes in descending order of score.
pad_to_bounding_box(...): Padimagewith zeros to the specifiedheightandwidth.
per_image_standardization(...): Linearly scalesimageto have zero mean and unit norm.
psnr(...): Returns the Peak Signal-to-Noise Ratio between a and b.
random_brightness(...): Adjust the brightness of images by a random factor.
random_contrast(...): Adjust the contrast of an image by a random factor.
random_flip_left_right(...): Randomly flip an image horizontally (left to right).
random_flip_up_down(...): Randomly flips an image vertically (upside down).
random_hue(...): Adjust the hue of an RGB image by a random factor.
random_saturation(...): Adjust the saturation of an RGB image by a random factor.
resize_area(...): Resizeimagestosizeusing area interpolation.
resize_bicubic(...): Resizeimagestosizeusing bicubic interpolation.
resize_bilinear(...): Resizeimagestosizeusing bilinear interpolation.
resize_image_with_crop_or_pad(...): Crops and/or pads an image to a target width and height.
resize_images(...): Resizeimagestosizeusing the specifiedmethod.
resize_nearest_neighbor(...): Resizeimagestosizeusing nearest neighbor interpolation.
rgb_to_grayscale(...): Converts one or more images from RGB to Grayscale.
rgb_to_hsv(...): Converts one or more images from RGB to HSV.
rgb_to_yiq(...): Converts one or more images from RGB to YIQ.
rgb_to_yuv(...): Converts one or more images from RGB to YUV.
rot90(...): Rotate image(s) counter-clockwise by 90 degrees.
sample_distorted_bounding_box(...): Generate a single randomly distorted bounding box for an image.
sobel_edges(...): Returns a tensor holding Sobel edge maps.
ssim(...): Computes SSIM index between img1 and img2.
ssim_multiscale(...): Computes the MS-SSIM between img1 and img2.
total_variation(...): Calculate and return the total variation for one or more images.
transpose_image(...): Transpose image(s) by swapping the height and width dimension.
yiq_to_rgb(...): Converts one or more images from YIQ to RGB.
yuv_to_rgb(...): Converts one or more images from YUV to RGB.
接下来，我们从中挑一些常用的详细了解一下。
decode_jpeg函数：
tf.image.decode_jpeg(
contents,
channels=0,
ratio=1,
fancy_upscaling=True,
try_recover_truncated=False,
acceptable_fraction=1,
dct_method='',
name=None
)
相应的，tensorflow也提供解码其他图片格式如png，gif，bmp等等。
这个函数将一个jpeg格式的图片解析为一个unit8的tensor。
参数列表中的channel表示转换后想要的颜色通道的个数。接收0（使用原jpeg通道个数），1（grayscale），3（rgb)
参数列表中的ratio表示降级（downscale）图片。 接收值有1，2，4，8.
未完待续ing。。。