我试图使用以下功能来裁剪大量的图像100,000。我是连续做这个操作，但是花了很多时间。有效的方法是什么？
tf.image.crop_to_bounding_box
以下是我的代码：
def crop_images(img_dir, list_images):
outlist=[]
with tf.Session() as session:
for image1 in list_images[:5]:
image = mpimg.imread(img_dir+image1)
x = tf.Variable(image, name='x')
data_t = tf.placeholder(tf.uint8)
op = tf.image.encode_jpeg(data_t, format='rgb')
model = tf.global_variables_initializer()
img_name = "img/"+image1.split("_img_0")[0] + "/img_0"+image1.split("_img_0")[1]
height = x.shape[1]
[x1,y1,x2,y2] = img_bbox_dict[img_name]
x = tf.image.crop_to_bounding_box(x, int(y1), int(x1), int(y2)-int(y1), int(x2)-int(x1))
session.run(model)
result = session.run(x)
data_np = session.run(op, feed_dict={ data_t: result })
with open(img_path+image1, 'w+') as fd:
fd.write(data_np)
我将给出Tensorflow程序员指南中关于读取数据的一个例子的简化版本，可以找到here。基本上，它使用Reader和Filename Queues使用指定数量的线程将图像数据批处理在一起。这些线程使用所谓的线程协调器进行协调。
import tensorflow as tf
import glob
images_path = "./" #RELATIVE glob pathname of current directory
images_extension = "*.png"
# Save the list of files matching pattern, so it is only computed once.
filenames = tf.train.match_filenames_once(glob.glob(images_path+images_extension))
batch_size = len(glob.glob1(images_path,images_extension))
num_epochs=1
standard_size = [500, 500]
num_channels = 3
min_after_dequeue = 10
num_preprocess_threads = 3
seed = 14131
"""
IMPORTANT: Cropping params. These are arbitrary values used only for this example.
You will have to change them according to your requirements.
"""
crop_size=[200,200]
boxes = [1,1,460,460]
"""
'WholeFileReader' is a Reader who's 'read' method outputs the next
key-value pair of the filename and the contents of the file (the image) from
the Queue, both of which are string scalar Tensors.
Note that the The QueueRunner works in a thread separate from the
Reader that pulls filenames from the queue, so the shuffling and enqueuing
process does not block the reader.
'resize_images' is used so that all images are resized to the same
size (Aspect ratios may change, so in that case use resize_image_with_crop_or_pad)
'set_shape' is used because the height and width dimensions of 'image' are
data dependent and cannot be computed without executing this operation. Without
this Op, the 'image' Tensor's shape will have None as Dimensions.
"""
def read_my_file_format(filename_queue, standard_size, num_channels):
image_reader = tf.WholeFileReader()
_, image_file = image_reader.read(filename_queue)
if "jpg" in images_extension:
image = tf.image.decode_jpeg(image_file)
elif "png" in images_extension:
image = tf.image.decode_png(image_file)
image = tf.image.resize_images(image, standard_size)
image.set_shape(standard_size+[num_channels])
print "Successfully read file!"
return image
"""
'string_input_producer' Enters matched filenames into a 'QueueRunner' FIFO Queue.
'shuffle_batch' creates batches by randomly shuffling tensors. The 'capacity'
argument controls the how long the prefetching is allowed to grow the queues.
'min_after_dequeue' defines how big a buffer we will randomly
sample from -- bigger means better shuffling but slower startup & more memory used.
'capacity' must be larger than 'min_after_dequeue' and the amount larger
determines the maximum we will prefetch.
Recommendation: min_after_dequeue + (num_threads + a small safety margin) * batch_size
"""
def input_pipeline(filenames, batch_size, num_epochs, standard_size, num_channels, min_after_dequeue, num_preprocess_threads, seed):
filename_queue = tf.train.string_input_producer(filenames, num_epochs=num_epochs, shuffle=True)
example = read_my_file_format(filename_queue, standard_size, num_channels)
capacity = min_after_dequeue + 3 * batch_size
example_batch = tf.train.shuffle_batch([example], batch_size=batch_size, capacity=capacity, min_after_dequeue=min_after_dequeue, num_threads=num_preprocess_threads, seed=seed, enqueue_many=False)
print "Batching Successful!"
return example_batch
"""
Any transformation on the image batch goes here. Refer the documentation
for the details of how the cropping is done using this function.
"""
def crop_batch(image_batch, batch_size, b_boxes, crop_size):
cropped_images = tf.image.crop_and_resize(image_batch, boxes=[b_boxes for _ in xrange(batch_size)], box_ind=[i for i in xrange(batch_size)], crop_size=crop_size)
print "Cropping Successful!"
return cropped_images
example_batch = input_pipeline(filenames, batch_size, num_epochs, standard_size, num_channels, min_after_dequeue, num_preprocess_threads, seed)
cropped_images = crop_batch(example_batch, batch_size, boxes, crop_size)
"""
if 'num_epochs' is not `None`, the 'string_input_producer' function creates local
counter `epochs`. Use `local_variables_initializer()` to initialize local variables.
'Coordinator' class implements a simple mechanism to coordinate the termination
of a set of threads. Any of the threads can call `coord.request_stop()` to ask for all
the threads to stop. To cooperate with the requests, each thread must check for
`coord.should_stop()` on a regular basis.
`coord.should_stop()` returns True` as soon as `coord.request_stop()` has been called.
A thread can report an exception to the coordinator as part of the `should_stop()`
call. The exception will be re-raised from the `coord.join()` call.
After a thread has called `coord.request_stop()` the other threads have a
fixed time to stop, this is called the 'stop grace period' and defaults to 2 minutes.
If any of the threads is still alive after the grace period expires `coord.join()`
raises a RuntimeError reporting the laggards.
IMPORTANT: 'start_queue_runners' starts threads for all queue runners collected in
the graph, & returns the list of all threads. This must be executed BEFORE running
any other training/inference/operation steps, or it will hang forever.
"""
with tf.Session() as sess:
_, _ = sess.run([tf.global_variables_initializer(), tf.local_variables_initializer()])
coord = tf.train.Coordinator()
threads = tf.train.start_queue_runners(sess=sess, coord=coord)
try:
while not coord.should_stop():
# Run training steps or whatever
cropped_images1 = sess.run(cropped_images)
print cropped_images1.shape
except tf.errors.OutOfRangeError:
print('Load and Process done -- epoch limit reached')
finally:
# When done, ask the threads to stop.
coord.request_stop()
coord.join(threads)
sess.close()