Tensorflow object detection API源码分析之如何处理数据
本文旨在分析Tensorflow object detection API读取到数据之后，如何进行一系列预处理操作
整个预处理流程：
1.批量读数据前，通过 data_augmentation_options 类指定预处理操作
data_augmentation_options一系列预处理操作在samples/configs/ssd_mobilenet_v2_coco.config中指定，例如：
data_augmentation_options {
random_horizontal_flip {
}
}
data_augmentation_options {
ssd_random_crop {
}
}trainer.py 从配置文件中读入指定的预处理操作
data_augmentation_options = [
preprocessor_builder.build(step)
for step in train_config.data_augmentation_options]object_detection/builders/preprocessor_builder.py 预处理的构建
"""Builder for preprocessing steps."""
import tensorflow as tf
from object_detection.core import preprocessor
from object_detection.protos import preprocessor_pb2
def _get_step_config_from_proto(preprocessor_step_config, step_name):
"""Returns the value of a field named step_name from proto.
Args:
preprocessor_step_config: A preprocessor_pb2.PreprocessingStep object.
step_name: Name of the field to get value from.
Returns:
result_dict: a sub proto message from preprocessor_step_config which will be
later converted to a dictionary.
Raises:
ValueError: If field does not exist in proto.
"""
for field, value in preprocessor_step_config.ListFields():
if field.name == step_name:
return value
raise ValueError('Could not get field %s from proto!', step_name)
def _get_dict_from_proto(config):
"""Helper function to put all proto fields into a dictionary.
For many preprocessing steps, there's an trivial 1-1 mapping from proto fields
to function arguments. This function automatically populates a dictionary with
the arguments from the proto.
Protos that CANNOT be trivially populated include:
* nested messages.
* steps that check if an optional field is set (ie. where None != 0).
* protos that don't map 1-1 to arguments (ie. list should be reshaped).
* fields requiring additional validation (ie. repeated field has n elements).
Args:
config: A protobuf object that does not violate the conditions above.
Returns:
result_dict: |config| converted into a python dictionary.
"""
result_dict = {}
for field, value in config.ListFields():
result_dict[field.name] = value
return result_dict
# A map from a PreprocessingStep proto config field name to the preprocessing
# function that should be used. The PreprocessingStep proto should be parsable
# with _get_dict_from_proto.
PREPROCESSING_FUNCTION_MAP = {
'normalize_image': preprocessor.normalize_image,
'random_pixel_value_scale': preprocessor.random_pixel_value_scale,
'random_image_scale': preprocessor.random_image_scale,
'random_rgb_to_gray': preprocessor.random_rgb_to_gray,
'random_adjust_brightness': preprocessor.random_adjust_brightness,
'random_adjust_contrast': preprocessor.random_adjust_contrast,
'random_adjust_hue': preprocessor.random_adjust_hue,
'random_adjust_saturation': preprocessor.random_adjust_saturation,
'random_distort_color': preprocessor.random_distort_color,
'random_jitter_boxes': preprocessor.random_jitter_boxes,
'random_crop_to_aspect_ratio': preprocessor.random_crop_to_aspect_ratio,
'random_black_patches': preprocessor.random_black_patches,
'rgb_to_gray': preprocessor.rgb_to_gray,
'scale_boxes_to_pixel_coordinates': (
preprocessor.scale_boxes_to_pixel_coordinates),
'subtract_channel_mean': preprocessor.subtract_channel_mean,
}
# A map to convert from preprocessor_pb2.ResizeImage.Method enum to
# tf.image.ResizeMethod.
RESIZE_METHOD_MAP = {
preprocessor_pb2.ResizeImage.AREA: tf.image.ResizeMethod.AREA,
preprocessor_pb2.ResizeImage.BICUBIC: tf.image.ResizeMethod.BICUBIC,
preprocessor_pb2.ResizeImage.BILINEAR: tf.image.ResizeMethod.BILINEAR,
preprocessor_pb2.ResizeImage.NEAREST_NEIGHBOR: (
tf.image.ResizeMethod.NEAREST_NEIGHBOR),
}
def build(preprocessor_step_config):
"""Builds preprocessing step based on the configuration.
Args:
preprocessor_step_config: PreprocessingStep configuration proto.
Returns:
function, argmap: A callable function and an argument map to call function
with.
Raises:
ValueError: On invalid configuration.
"""
step_type = preprocessor_step_config.WhichOneof('preprocessing_step')
if step_type in PREPROCESSING_FUNCTION_MAP:
preprocessing_function = PREPROCESSING_FUNCTION_MAP[step_type]
step_config = _get_step_config_from_proto(preprocessor_step_config,
step_type)
function_args = _get_dict_from_proto(step_config)
return (preprocessing_function, function_args)
if step_type == 'random_horizontal_flip':
config = preprocessor_step_config.random_horizontal_flip
return (preprocessor.random_horizontal_flip,
{
'keypoint_flip_permutation': tuple(
config.keypoint_flip_permutation),
})
if step_type == 'random_vertical_flip':
config = preprocessor_step_config.random_vertical_flip
return (preprocessor.random_vertical_flip,
{
'keypoint_flip_permutation': tuple(
config.keypoint_flip_permutation),
})
if step_type == 'random_rotation90':
return (preprocessor.random_rotation90, {})
if step_type == 'random_crop_image':
config = preprocessor_step_config.random_crop_image
return (preprocessor.random_crop_image,
{
'min_object_covered': config.min_object_covered,
'aspect_ratio_range': (config.min_aspect_ratio,
config.max_aspect_ratio),
'area_range': (config.min_area, config.max_area),
'overlap_thresh': config.overlap_thresh,
'random_coef': config.random_coef,
})
if step_type == 'random_pad_image':
config = preprocessor_step_config.random_pad_image
min_image_size = None
if (config.HasField('min_image_height') !=
config.HasField('min_image_width')):
raise ValueError('min_image_height and min_image_width should be either '
'both set or both unset.')
if config.HasField('min_image_height'):
min_image_size = (config.min_image_height, config.min_image_width)
max_image_size = None
if (config.HasField('max_image_height') !=
config.HasField('max_image_width')):
raise ValueError('max_image_height and max_image_width should be either '
'both set or both unset.')
if config.HasField('max_image_height'):
max_image_size = (config.max_image_height, config.max_image_width)
pad_color = config.pad_color
if pad_color and len(pad_color) != 3:
raise ValueError('pad_color should have 3 elements (RGB) if set!')
if not pad_color:
pad_color = None
return (preprocessor.random_pad_image,
{
'min_image_size': min_image_size,
'max_image_size': max_image_size,
'pad_color': pad_color,
})
if step_type == 'random_crop_pad_image':
config = preprocessor_step_config.random_crop_pad_image
min_padded_size_ratio = config.min_padded_size_ratio
if min_padded_size_ratio and len(min_padded_size_ratio) != 2:
raise ValueError('min_padded_size_ratio should have 2 elements if set!')
max_padded_size_ratio = config.max_padded_size_ratio
if max_padded_size_ratio and len(max_padded_size_ratio) != 2:
raise ValueError('max_padded_size_ratio should have 2 elements if set!')
pad_color = config.pad_color
if pad_color and len(pad_color) != 3:
raise ValueError('pad_color should have 3 elements if set!')
kwargs = {
'min_object_covered': config.min_object_covered,
'aspect_ratio_range': (config.min_aspect_ratio,
config.max_aspect_ratio),
'area_range': (config.min_area, config.max_area),
'overlap_thresh': config.overlap_thresh,
'random_coef': config.random_coef,
}
if min_padded_size_ratio:
kwargs['min_padded_size_ratio'] = tuple(min_padded_size_ratio)
if max_padded_size_ratio:
kwargs['max_padded_size_ratio'] = tuple(max_padded_size_ratio)
if pad_color:
kwargs['pad_color'] = tuple(pad_color)
return (preprocessor.random_crop_pad_image, kwargs)
if step_type == 'random_resize_method':
config = preprocessor_step_config.random_resize_method
return (preprocessor.random_resize_method,
{
'target_size': [config.target_height, config.target_width],
})
if step_type == 'resize_image':
config = preprocessor_step_config.resize_image
method = RESIZE_METHOD_MAP[config.method]
return (preprocessor.resize_image,
{
'new_height': config.new_height,
'new_width': config.new_width,
'method': method
})
if step_type == 'ssd_random_crop':
config = preprocessor_step_config.ssd_random_crop
if config.operations:
min_object_covered = [op.min_object_covered for op in config.operations]
aspect_ratio_range = [(op.min_aspect_ratio, op.max_aspect_ratio)
for op in config.operations]
area_range = [(op.min_area, op.max_area) for op in config.operations]
overlap_thresh = [op.overlap_thresh for op in config.operations]
random_coef = [op.random_coef for op in config.operations]
return (preprocessor.ssd_random_crop,
{
'min_object_covered': min_object_covered,
'aspect_ratio_range': aspect_ratio_range,
'area_range': area_range,
'overlap_thresh': overlap_thresh,
'random_coef': random_coef,
})
return (preprocessor.ssd_random_crop, {})
if step_type == 'ssd_random_crop_pad':
config = preprocessor_step_config.ssd_random_crop_pad
if config.operations:
min_object_covered = [op.min_object_covered for op in config.operations]
aspect_ratio_range = [(op.min_aspect_ratio, op.max_aspect_ratio)
for op in config.operations]
area_range = [(op.min_area, op.max_area) for op in config.operations]
overlap_thresh = [op.overlap_thresh for op in config.operations]
random_coef = [op.random_coef for op in config.operations]
min_padded_size_ratio = [tuple(op.min_padded_size_ratio)
for op in config.operations]
max_padded_size_ratio = [tuple(op.max_padded_size_ratio)
for op in config.operations]
pad_color = [(op.pad_color_r, op.pad_color_g, op.pad_color_b)
for op in config.operations]
return (preprocessor.ssd_random_crop_pad,
{
'min_object_covered': min_object_covered,
'aspect_ratio_range': aspect_ratio_range,
'area_range': area_range,
'overlap_thresh': overlap_thresh,
'random_coef': random_coef,
'min_padded_size_ratio': min_padded_size_ratio,
'max_padded_size_ratio': max_padded_size_ratio,
'pad_color': pad_color,
})
return (preprocessor.ssd_random_crop_pad, {})
if step_type == 'ssd_random_crop_fixed_aspect_ratio':
config = preprocessor_step_config.ssd_random_crop_fixed_aspect_ratio
if config.operations:
min_object_covered = [op.min_object_covered for op in config.operations]
area_range = [(op.min_area, op.max_area) for op in config.operations]
overlap_thresh = [op.overlap_thresh for op in config.operations]
random_coef = [op.random_coef for op in config.operations]
return (preprocessor.ssd_random_crop_fixed_aspect_ratio,
{
'min_object_covered': min_object_covered,
'aspect_ratio': config.aspect_ratio,
'area_range': area_range,
'overlap_thresh': overlap_thresh,
'random_coef': random_coef,
})
return (preprocessor.ssd_random_crop_fixed_aspect_ratio, {})
if step_type == 'ssd_random_crop_pad_fixed_aspect_ratio':
config = preprocessor_step_config.ssd_random_crop_pad_fixed_aspect_ratio
kwargs = {}
aspect_ratio = config.aspect_ratio
if aspect_ratio:
kwargs['aspect_ratio'] = aspect_ratio
min_padded_size_ratio = config.min_padded_size_ratio
if min_padded_size_ratio:
if len(min_padded_size_ratio) != 2:
raise ValueError('min_padded_size_ratio should have 2 elements if set!')
kwargs['min_padded_size_ratio'] = tuple(min_padded_size_ratio)
max_padded_size_ratio = config.max_padded_size_ratio
if max_padded_size_ratio:
if len(max_padded_size_ratio) != 2:
raise ValueError('max_padded_size_ratio should have 2 elements if set!')
kwargs['max_padded_size_ratio'] = tuple(max_padded_size_ratio)
if config.operations:
kwargs['min_object_covered'] = [op.min_object_covered
for op in config.operations]
kwargs['aspect_ratio_range'] = [(op.min_aspect_ratio, op.max_aspect_ratio)
for op in config.operations]
kwargs['area_range'] = [(op.min_area, op.max_area)
for op in config.operations]
kwargs['overlap_thresh'] = [op.overlap_thresh for op in config.operations]
kwargs['random_coef'] = [op.random_coef for op in config.operations]
return (preprocessor.ssd_random_crop_pad_fixed_aspect_ratio, kwargs)
raise ValueError('Unknown preprocessing step.')
目前支持的预处理操作有如下多种，所有的预处理操作详见core/preprocessor.py：
normalize_image
random_pixel_value_scale
random_image_scale
random_rgb_to_gray
random_adjust_brightness
random_adjust_contrast
random_adjust_hue
random_adjust_saturation
random_distort_color
random_jitter_boxes 随机抖动boxes
random_crop_to_aspect_ratio
random_black_patches
rgb_to_gray
scale_boxes_to_pixel_coordinates
subtract_channel_mean
random_horizontal_flip
random_vertical_flip
random_rotation90
random_pad_image
random_crop_pad_image
random_resize_method
resize_image
ssd_random_crop
ssd_random_crop_pad
ssd_random_crop_fixed_aspect_ratio
ssd_random_crop_pad_fixed_aspect_ratio
2.批量数据读取：创建两个队列
队列1 ： 开启 N 个线程，每个线程从数据集依次读一条数据，写入队列 1。一个线程从队列 1 每次读 batch_size 条数据
队列2：将队列 1 出队列的数据写入队列 2， 当调用 dequeue 的事实，从队列 2 读取 batch_size 的数据。
批量读数据后，通过 模型的预处理函数进行预处理 detection_model.preprocess 之后，喂给模型。
trainer.py
def create_input_queue(batch_size_per_clone, create_tensor_dict_fn,
batch_queue_capacity, num_batch_queue_threads,
prefetch_queue_capacity, data_augmentation_options):
"""Sets up reader, prefetcher and returns input queue.
Args:
batch_size_per_clone: batch size to use per clone.
create_tensor_dict_fn: function to create tensor dictionary.
batch_queue_capacity: maximum number of elements to store within a queue.
num_batch_queue_threads: number of threads to use for batching.
prefetch_queue_capacity: maximum capacity of the queue used to prefetch
assembled batches.
data_augmentation_options: a list of tuples, where each tuple contains a
data augmentation function and a dictionary containing arguments and their
values (see preprocessor.py).
Returns:
input queue: a batcher.BatchQueue object holding enqueued tensor_dicts
(which hold images, boxes and targets). To get a batch of tensor_dicts,
call input_queue.Dequeue().
"""
#读一条数据
tensor_dict = create_tensor_dict_fn()
#增加维度
tensor_dict[fields.InputDataFields.image] = tf.expand_dims(
tensor_dict[fields.InputDataFields.image], 0)
#将图像转化为float
images = tensor_dict[fields.InputDataFields.image]
float_images = tf.to_float(images)
tensor_dict[fields.InputDataFields.image] = float_images
#是否包含 instance_masks
include_instance_masks = (fields.InputDataFields.groundtruth_instance_masks
in tensor_dict)
#是否包含关键点
include_keypoints = (fields.InputDataFields.groundtruth_keypoints
in tensor_dict)
#是否包含多标签
include_multiclass_scores = (fields.InputDataFields.multiclass_scores
in tensor_dict)
#预处理数据增强
if data_augmentation_options:
tensor_dict = preprocessor.preprocess(
tensor_dict, data_augmentation_options,
func_arg_map=preprocessor.get_default_func_arg_map(
include_label_weights=True,
include_multiclass_scores=include_multiclass_scores,
include_instance_masks=include_instance_masks,
include_keypoints=include_keypoints))
#创建两个队列
#队列1：开启num_batch_queue_threads个线程，每个线程从数据集依次读一条数据，写入队列
#一个线程从队列每次读batchisze条数据
#队列2：从队列1出队列的数据写入队列2，容量为prefetch_queue_capacity，当调用 dequeue 的时候，从队列 2 读取 batch_size 的数据。
input_queue = batcher.BatchQueue(
tensor_dict,
batch_size=batch_size_per_clone,
batch_queue_capacity=batch_queue_capacity,
num_batch_queue_threads=num_batch_queue_threads,
prefetch_queue_capacity=prefetch_queue_capacity)
return input_queue
def get_inputs(input_queue,
num_classes,
merge_multiple_label_boxes=False,
use_multiclass_scores=False):
"""Dequeues batch and constructs inputs to object detection model.
Args:
input_queue: BatchQueue object holding enqueued tensor_dicts.
num_classes: Number of classes.
merge_multiple_label_boxes: Whether to merge boxes with multiple labels
or not. Defaults to false. Merged boxes are represented with a single
box and a k-hot encoding of the multiple labels associated with the
boxes.
use_multiclass_scores: Whether to use multiclass scores instead of
groundtruth_classes.
Returns:
images: a list of 3-D float tensor of images.
image_keys: a list of string keys for the images.
locations_list: a list of tensors of shape [num_boxes, 4]
containing the corners of the groundtruth boxes.
classes_list: a list of padded one-hot (or K-hot) float32 tensors containing
target classes.
masks_list: a list of 3-D float tensors of shape [num_boxes, image_height,
image_width] containing instance masks for objects if present in the
input_queue. Else returns None.
keypoints_list: a list of 3-D float tensors of shape [num_boxes,
num_keypoints, 2] containing keypoints for objects if present in the
input queue. Else returns None.
weights_lists: a list of 1-D float32 tensors of shape [num_boxes]
containing groundtruth weight for each box.
"""
#从预提取队列中取一份数据[batchsize,height,width,3]
read_data_list = input_queue.dequeue()
label_id_offset = 1
#解析读到的数据
def extract_images_and_targets(read_data):
"""Extract images and targets from the input dict."""
image = read_data[fields.InputDataFields.image]
key = ''
if fields.InputDataFields.source_id in read_data:
key = read_data[fields.InputDataFields.source_id]
location_gt = read_data[fields.InputDataFields.groundtruth_boxes]
classes_gt = tf.cast(read_data[fields.InputDataFields.groundtruth_classes],
tf.int32)
classes_gt -= label_id_offset
if merge_multiple_label_boxes and use_multiclass_scores:
raise ValueError(
'Using both merge_multiple_label_boxes and use_multiclass_scores is'
'not supported'
)
if merge_multiple_label_boxes:
location_gt, classes_gt, _ = util_ops.merge_boxes_with_multiple_labels(
location_gt, classes_gt, num_classes)
classes_gt = tf.cast(classes_gt, tf.float32)
elif use_multiclass_scores:
classes_gt = tf.cast(read_data[fields.InputDataFields.multiclass_scores],
tf.float32)
else:
classes_gt = util_ops.padded_one_hot_encoding(
indices=classes_gt, depth=num_classes, left_pad=0)
masks_gt = read_data.get(fields.InputDataFields.groundtruth_instance_masks)
keypoints_gt = read_data.get(fields.InputDataFields.groundtruth_keypoints)
if (merge_multiple_label_boxes and (
masks_gt is not None or keypoints_gt is not None)):
raise NotImplementedError('Multi-label support is only for boxes.')
weights_gt = read_data.get(
fields.InputDataFields.groundtruth_weights)
return (image, key, location_gt, classes_gt, masks_gt, keypoints_gt,
weights_gt)
return zip(*map(extract_images_and_targets, read_data_list))"""Provides functions to batch a dictionary of input tensors."""
import collections
import tensorflow as tf
from object_detection.core import prefetcher
rt_shape_str = '_runtime_shapes'
# 创建两个对队列，
# 队列1 ： 开启 num_batch_queue_threads 个线程，每个线程从数据集依次读一条数据，写入队列。
# 一个线程从队列每次读 batch_size 条数据
# 队列2 ： 将队列 1 出队列的数据写入队列 2，容量为 prefetch_queue_capacity。当调用 dequeue 的时候，从队列 2 读取 batch_size 的数据。队列 2 中每个元素的容量为 [batch_size, height, width, 3]
class BatchQueue(object):
"""BatchQueue class.
This class creates a batch queue to asynchronously enqueue tensors_dict.
It also adds a FIFO prefetcher so that the batches are readily available
for the consumers. Dequeue ops for a BatchQueue object can be created via
the Dequeue method which evaluates to a batch of tensor_dict.
Example input pipeline with batching:
------------------------------------
key, string_tensor = slim.parallel_reader.parallel_read(...)
tensor_dict = decoder.decode(string_tensor)
tensor_dict = preprocessor.preprocess(tensor_dict, ...)
batch_queue = batcher.BatchQueue(tensor_dict,
batch_size=32,
batch_queue_capacity=2000,
num_batch_queue_threads=8,
prefetch_queue_capacity=20)
tensor_dict = batch_queue.dequeue()
outputs = Model(tensor_dict)
...
-----------------------------------
Notes:
-----
This class batches tensors of unequal sizes by zero padding and unpadding
them after generating a batch. This can be computationally expensive when
batching tensors (such as images) that are of vastly different sizes. So it is
recommended that the shapes of such tensors be fully defined in tensor_dict
while other lightweight tensors such as bounding box corners and class labels
can be of varying sizes. Use either crop or resize operations to fully define
the shape of an image in tensor_dict.
It is also recommended to perform any preprocessing operations on tensors
before passing to BatchQueue and subsequently calling the Dequeue method.
Another caveat is that this class does not read the last batch if it is not
full. The current implementation makes it hard to support that use case. So,
for evaluation, when it is critical to run all the examples through your
network use the input pipeline example mentioned in core/prefetcher.py.
"""
def __init__(self, tensor_dict, batch_size, batch_queue_capacity,
num_batch_queue_threads, prefetch_queue_capacity):
"""Constructs a batch queue holding tensor_dict.
Args:
tensor_dict: dictionary of tensors to batch.
batch_size: batch size.
batch_queue_capacity: max capacity of the queue from which the tensors are
batched.
num_batch_queue_threads: number of threads to use for batching.
prefetch_queue_capacity: max capacity of the queue used to prefetch
assembled batches.
"""
# Remember static shapes to set shapes of batched tensors.
static_shapes = collections.OrderedDict(
{key: tensor.get_shape() for key, tensor in tensor_dict.items()})
# Remember runtime shapes to unpad tensors after batching.
runtime_shapes = collections.OrderedDict(
{(key + rt_shape_str): tf.shape(tensor)
for key, tensor in tensor_dict.items()})
all_tensors = tensor_dict
all_tensors.update(runtime_shapes)
# 创建一个 PaddingFIFOQueue 队列，容量为 batch_queue_capacity，
# 开启 num_batch_queue_threads 线程， 每个线程一次从 all_tensors 读一条数据写入，一直到队列满为止
# 从队列每次读 batch_size 条数据，并返回
batched_tensors = tf.train.batch(
all_tensors,
capacity=batch_queue_capacity,
batch_size=batch_size,
dynamic_pad=True,
num_threads=num_batch_queue_threads)
# 创建容量为 prefetch_queue_capacity 的 PaddingFIFOQueue
# 创建一个线程将 batched_tensors 加入队列。
self._queue = prefetcher.prefetch(batched_tensors,
prefetch_queue_capacity)
self._static_shapes = static_shapes
self._batch_size = batch_size
def dequeue(self):
"""Dequeues a batch of tensor_dict from the BatchQueue.
TODO: use allow_smaller_final_batch to allow running over the whole eval set
Returns:
A list of tensor_dicts of the requested batch_size.
"""
# 从 prefetch 队列取一份数据 (size 为 batch_size)
batched_tensors = self._queue.dequeue()
# Separate input tensors from tensors containing their runtime shapes.
tensors = {}
shapes = {}
for key, batched_tensor in batched_tensors.items():
unbatched_tensor_list = tf.unstack(batched_tensor)
for i, unbatched_tensor in enumerate(unbatched_tensor_list):
if rt_shape_str in key:
shapes[(key[:-len(rt_shape_str)], i)] = unbatched_tensor
else:
tensors[(key, i)] = unbatched_tensor
# Undo that padding using shapes and create a list of size `batch_size` that
# contains tensor dictionaries.
tensor_dict_list = []
batch_size = self._batch_size
for batch_id in range(batch_size):
tensor_dict = {}
for key in self._static_shapes:
tensor_dict[key] = tf.slice(tensors[(key, batch_id)],
tf.zeros_like(shapes[(key, batch_id)]),
shapes[(key, batch_id)])
tensor_dict[key].set_shape(self._static_shapes[key])
tensor_dict_list.append(tensor_dict)
return tensor_dict_list
prefetch.py
import tensorflow as tf
def prefetch(tensor_dict, capacity):
"""Creates a prefetch queue for tensors.
Creates a FIFO queue to asynchronously enqueue tensor_dicts and returns a
dequeue op that evaluates to a tensor_dict. This function is useful in
prefetching preprocessed tensors so that the data is readily available for
consumers.
Example input pipeline when you don't need batching:
----------------------------------------------------
key, string_tensor = slim.parallel_reader.parallel_read(...)
tensor_dict = decoder.decode(string_tensor)
tensor_dict = preprocessor.preprocess(tensor_dict, ...)
prefetch_queue = prefetcher.prefetch(tensor_dict, capacity=20)
tensor_dict = prefetch_queue.dequeue()
outputs = Model(tensor_dict)
...
----------------------------------------------------
For input pipelines with batching, refer to core/batcher.py
Args:
tensor_dict: a dictionary of tensors to prefetch.
capacity: the size of the prefetch queue.
Returns:
a FIFO prefetcher queue
"""
names = list(tensor_dict.keys())
dtypes = [t.dtype for t in tensor_dict.values()]
shapes = [t.get_shape() for t in tensor_dict.values()]
prefetch_queue = tf.PaddingFIFOQueue(capacity, dtypes=dtypes,
shapes=shapes,
names=names,
name='prefetch_queue')
enqueue_op = prefetch_queue.enqueue(tensor_dict)
tf.train.queue_runner.add_queue_runner(tf.train.queue_runner.QueueRunner(
prefetch_queue, [enqueue_op]))
tf.summary.scalar('queue/%s/fraction_of_%d_full' % (prefetch_queue.name,
capacity),
tf.to_float(prefetch_queue.size()) * (1. / capacity))
return prefetch_queue
参考：https://blog.csdn.net/wenxueliu/article/details/80727911