Data Loading API¶

Overview¶

This document summarizes supported data formats and iterator APIs to read the data including

`mxnet.io`	Data iterators for common data formats.
`mxnet.recordio`	Read and write for the RecordIO data format.
`mxnet.image`	Image Iterators and image augmentation functions

First, let’s see how to write an iterator for a new data format. The following iterator can be used to train a symbol whose input data variable has name data and input label variable has name softmax_label. The iterator also provides information about the batch, including the shapes and name.

>>> nd_iter = mx.io.NDArrayIter(data={'data':mx.nd.ones((100,10))},
...                             label={'softmax_label':mx.nd.ones((100,))},
...                             batch_size=25)
>>> print(nd_iter.provide_data)
[DataDesc[data,(25, 10L),,NCHW]]
>>> print(nd_iter.provide_label)
[DataDesc[softmax_label,(25,),,NCHW]]

Let’s see a complete example of how to use data iterator in model training.

>>> data = mx.sym.Variable('data')
>>> label = mx.sym.Variable('softmax_label')
>>> fullc = mx.sym.FullyConnected(data=data, num_hidden=1)
>>> loss = mx.sym.SoftmaxOutput(data=data, label=label)
>>> mod = mx.mod.Module(loss, data_names=['data'], label_names=['softmax_label'])
>>> mod.bind(data_shapes=nd_iter.provide_data, label_shapes=nd_iter.provide_label)
>>> mod.fit(nd_iter, num_epoch=2)

A detailed tutorial is available at Iterators - Loading data.

Data iterators¶

`io.NDArrayIter`	Returns an iterator for `mx.nd.NDArray`, `numpy.ndarray` or `h5py.Dataset`.
`io.CSVIter`	Returns the CSV file iterator.
`io.ImageRecordIter`	Iterates on image RecordIO files
`io.ImageRecordUInt8Iter`	Iterating on image RecordIO files
`io.MNISTIter`	Iterating on the MNIST dataset.
`recordio.MXRecordIO`	Reads/writes RecordIO data format, supporting sequential read and write.
`recordio.MXIndexedRecordIO`	Reads/writes RecordIO data format, supporting random access.
`image.ImageIter`	Image data iterator with a large number of augmentation choices.
`image.ImageDetIter`	Image iterator with a large number of augmentation choices for detection.

Helper classes and functions¶

Data structures and other iterators provided in the mxnet.io packages.

`io.DataDesc`	DataDesc is used to store name, shape, type and layout information of the data or the label.
`io.DataBatch`	A data batch.
`io.DataIter`	The base class for an MXNet data iterator.
`io.ResizeIter`	Resize a data iterator to a given number of batches.
`io.PrefetchingIter`	Performs pre-fetch for other data iterators.
`io.MXDataIter`	A python wrapper a C++ data iterator.

Functions to read and write RecordIO files.

`recordio.pack`	Pack a string into MXImageRecord.
`recordio.unpack`	Unpack a MXImageRecord to string.
`recordio.unpack_img`	Unpack a MXImageRecord to image.
`recordio.pack_img`	Pack an image into `MXImageRecord`.

Develop a new iterator¶

Writing a new data iterator in Python is straightforward. Most MXNet training/inference programs accept an iterable object with provide_data and provide_label properties. This tutorial explains how to write an iterator from scratch.

The following example demonstrates how to combine multiple data iterators into a single one. It can be used for multiple modality training such as image captioning, in which images are read by ImageRecordIter while documents are read by CSVIter

class MultiIter:
    def __init__(self, iter_list):
        self.iters = iter_list
    def next(self):
        batches = [i.next() for i in self.iters]
        return DataBatch(data=[*b.data for b in batches],
                         label=[*b.label for b in batches])
    def reset(self):
        for i in self.iters:
            i.reset()
    @property
    def provide_data(self):
        return [*i.provide_data for i in self.iters]
    @property
    def provide_label(self):
        return [*i.provide_label for i in self.iters]

iter = MultiIter([mx.io.ImageRecordIter('image.rec'), mx.io.CSVIter('txt.csv')])

Parsing and performing another pre-processing such as augmentation may be expensive. If performance is critical, we can implement a data iterator in C++. Refer to src/io for examples.

Change batch layout¶

By default, the backend engine treats the first dimension of each data and label variable in data iterators as the batch size (i.e. NCHW or NT layout). In order to override the axis for batch size, the provide_data (and provide_label if there is label) properties should include the layouts. This is especially useful in RNN since TNC layouts are often more efficient. For example:

@property
def provide_data(self):
    return [DataDesc(name='seq_var', shape=(seq_length, batch_size), layout='TN')]

The backend engine will recognize the index of N in the layout as the axis for batch size.

API Reference¶

Data iterators for common data formats.

class mxnet.io.DataDesc[source]¶

DataDesc is used to store name, shape, type and layout information of the data or the label.

The layout describes how the axes in shape should be interpreted, for example for image data setting layout=NCHW indicates that the first axis is number of examples in the batch(N), C is number of channels, H is the height and W is the width of the image.

For sequential data, by default layout is set to NTC, where N is number of examples in the batch, T the temporal axis representing time and C is the number of channels.

Parameters:	cls (DataDesc) – The class. name (str) – Data name. shape (tuple of int) – Data shape. dtype (np.dtype, optional) – Data type. layout (str, optional) – Data layout.

static get_batch_axis(layout)[source]¶

Get the dimension that corresponds to the batch size.

When data parallelism is used, the data will be automatically split and concatenated along the batch-size dimension. Axis can be -1, which means the whole array will be copied for each data-parallelism device.

Parameters:	layout (str) – layout string. For example, “NCHW”.
Returns:	An axis indicating the batch_size dimension.
Return type:	int

static get_list(shapes, types)[source]¶

Get DataDesc list from attribute lists.

Parameters:	shapes (a tuple of (name, shape)) – types (a tuple of (name, type)) –

class mxnet.io.DataBatch(data, label=None, pad=None, index=None, bucket_key=None, provide_data=None, provide_label=None)[source]¶

A data batch.

MXNet’s data iterator returns a batch of data for each next call. This data contains batch_size number of examples.

If the input data consists of images, then shape of these images depend on the layout attribute of DataDesc object in provide_data parameter.

If layout is set to ‘NCHW’ then, images should be stored in a 4-D matrix of shape (batch_size, num_channel, height, width). If layout is set to ‘NHWC’ then, images should be stored in a 4-D matrix of shape (batch_size, height, width, num_channel). The channels are often in RGB order.

Parameters:

data (list of NDArray, each array containing batch_size examples.) – A list of input data.
label (list of NDArray, each array often containing a 1-dimensional array. optional) – A list of input labels.
pad (int, optional) – The number of examples padded at the end of a batch. It is used when the total number of examples read is not divisible by the batch_size. These extra padded examples are ignored in prediction.
index (numpy.array, optional) – The example indices in this batch.
bucket_key (int, optional) – The bucket key, used for bucketing module.
provide_data (list of DataDesc, optional) – A list of DataDesc objects. DataDesc is used to store name, shape, type and layout information of the data. The i-th element describes the name and shape of data[i].
provide_label (list of DataDesc, optional) – A list of DataDesc objects. DataDesc is used to store name, shape, type and layout information of the label. The i-th element describes the name and shape of label[i].

class mxnet.io.DataIter(batch_size=0)[source]¶

The base class for an MXNet data iterator.

All I/O in MXNet is handled by specializations of this class. Data iterators in MXNet are similar to standard-iterators in Python. On each call to next they return a DataBatch which represents the next batch of data. When there is no more data to return, it raises a StopIteration exception.

Parameters:	batch_size (int, optional) – The batch size, namely the number of items in the batch.

See also

src/io : The underlying C++ data iterator implementation, e.g., CSVIter.

mxnet.io.CSVIter(*args, **kwargs)¶

Returns the CSV file iterator.

In this function, the data_shape parameter is used to set the shape of each line of the input data. If a row in an input file is 1,2,3,4,5,6` and data_shape is (3,2), that row will be reshaped, yielding the array [[1,2],[3,4],[5,6]] of shape (3,2).

By default, the CSVIter has round_batch parameter set to True. So, if batch_size is 3 and there are 4 total rows in CSV file, 2 more examples are consumed at the first round. If reset function is called after first round, the call is ignored and remaining examples are returned in the second round.

If one wants all the instances in the second round after calling reset, make sure to set round_batch to False.

If data_csv = 'data/' is set, then all the files in this directory will be read.

Examples:

// Contents of CSV file ``data/data.csv``.
1,2,3
2,3,4
3,4,5
4,5,6

// Creates a `CSVIter` with `batch_size`=2 and default `round_batch`=True.
CSVIter = mx.io.CSVIter(data_csv = 'data/data.csv', data_shape = (3,),
batch_size = 2)

// Two batches read from the above iterator are as follows:
[[ 1.  2.  3.]
[ 2.  3.  4.]]
[[ 3.  4.  5.]
[ 4.  5.  6.]]

// Creates a `CSVIter` with default `round_batch` set to True.
CSVIter = mx.io.CSVIter(data_csv = 'data/data.csv', data_shape = (3,),
batch_size = 3)

// Two batches read from the above iterator in the first pass are as follows:
[[1.  2.  3.]
[2.  3.  4.]
[3.  4.  5.]]

[[4.  5.  6.]
[1.  2.  3.]
[2.  3.  4.]]

// Now, `reset` method is called.
CSVIter.reset()

// Batch read from the above iterator in the second pass is as follows:
[[ 3.  4.  5.]
[ 4.  5.  6.]
[ 1.  2.  3.]]

// Creates a `CSVIter` with `round_batch`=False.
CSVIter = mx.io.CSVIter(data_csv = 'data/data.csv', data_shape = (3,),
batch_size = 3, round_batch=False)

// Contents of two batches read from the above iterator in both passes, after calling
// `reset` method before second pass, is as follows:
[[1.  2.  3.]
[2.  3.  4.]
[3.  4.  5.]]

[[4.  5.  6.]
[2.  3.  4.]
[3.  4.  5.]]

Defined in src/io/iter_csv.cc:L220

Parameters:	data_csv (string, required) – The input CSV file or a directory path. data_shape (Shape(tuple), required) – The shape of one example. label_csv (string, optional, default='NULL') – The input CSV file or a directory path. If NULL, all labels will be returned as 0. label_shape (Shape(tuple), optional, default=(1,)) – The shape of one label. batch_size (int (non-negative), required) – Batch size. round_batch (boolean, optional, default=True) – Whether to use round robin to handle overflow batch or not. prefetch_buffer (long (non-negative), optional, default=4) – Maximum number of batches to prefetch. dtype ({None, 'float16', 'float32', 'float64', 'int32', 'uint8'},optional, default='None') – Output data type. `None` means no change.
Returns:	The result iterator.
Return type:	MXDataIter

mxnet.io.ImageDetRecordIter(*args, **kwargs)¶

Create iterator for image detection dataset packed in recordio.

Parameters:	path_imglist (string, optional, default='') – Dataset Param: Path to image list. path_imgrec (string, optional, default='./data/imgrec.rec') – Dataset Param: Path to image record file. aug_seq (string, optional, default='det_aug_default') – Augmentation Param: the augmenter names to represent sequence of augmenters to be applied, seperated by comma. Additional keyword parameters will be seen by these augmenters. Make sure you don’t use normal augmenters for detection tasks. label_width (int, optional, default='-1') – Dataset Param: How many labels for an image, -1 for variable label size. data_shape (Shape(tuple), required) – Dataset Param: Shape of each instance generated by the DataIter. preprocess_threads (int, optional, default='4') – Backend Param: Number of thread to do preprocessing. verbose (boolean, optional, default=True) – Auxiliary Param: Whether to output parser information. num_parts (int, optional, default='1') – partition the data into multiple parts part_index (int, optional, default='0') – the index of the part will read shuffle_chunk_size (long (non-negative), optional, default=0) – the size(MB) of the shuffle chunk, used with shuffle=True, it can enable global shuffling shuffle_chunk_seed (int, optional, default='0') – the seed for chunk shuffling label_pad_width (int, optional, default='0') – pad output label width if set larger than 0, -1 for auto estimate label_pad_value (float, optional, default=-1) – label padding value if enabled shuffle (boolean, optional, default=False) – Augmentation Param: Whether to shuffle data. seed (int, optional, default='0') – Augmentation Param: Random Seed. batch_size (int (non-negative), required) – Batch size. round_batch (boolean, optional, default=True) – Whether to use round robin to handle overflow batch or not. prefetch_buffer (long (non-negative), optional, default=4) – Maximum number of batches to prefetch. dtype ({None, 'float16', 'float32', 'float64', 'int32', 'uint8'},optional, default='None') – Output data type. `None` means no change. resize (int, optional, default='-1') – Augmentation Param: scale shorter edge to size before applying other augmentations, -1 to disable. rand_crop_prob (float, optional, default=0) – Augmentation Param: Probability of random cropping, <= 0 to disable min_crop_scales (, optional, default=(0,)) – Augmentation Param: Min crop scales. max_crop_scales (, optional, default=(1,)) – Augmentation Param: Max crop scales. min_crop_aspect_ratios (, optional, default=(1,)) – Augmentation Param: Min crop aspect ratios. max_crop_aspect_ratios (, optional, default=(1,)) – Augmentation Param: Max crop aspect ratios. min_crop_overlaps (, optional, default=(0,)) – Augmentation Param: Minimum crop IOU between crop_box and ground-truths. max_crop_overlaps (, optional, default=(1,)) – Augmentation Param: Maximum crop IOU between crop_box and ground-truth. min_crop_sample_coverages (, optional, default=(0,)) – Augmentation Param: Minimum ratio of intersect/crop_area between crop box and ground-truths. max_crop_sample_coverages (, optional, default=(1,)) – Augmentation Param: Maximum ratio of intersect/crop_area between crop box and ground-truths. min_crop_object_coverages (, optional, default=(0,)) – Augmentation Param: Minimum ratio of intersect/gt_area between crop box and ground-truths. max_crop_object_coverages (, optional, default=(1,)) – Augmentation Param: Maximum ratio of intersect/gt_area between crop box and ground-truths. num_crop_sampler (int, optional, default='1') – Augmentation Param: Number of crop samplers. crop_emit_mode ({'center', 'overlap'},optional, default='center') – Augmentation Param: Emition mode for invalid ground-truths after crop. center: emit if centroid of object is out of crop region; overlap: emit if overlap is less than emit_overlap_thresh. emit_overlap_thresh (float, optional, default=0.3) – Augmentation Param: Emit overlap thresh for emit mode overlap only. max_crop_trials (Shape(tuple), optional, default=(25,)) – Augmentation Param: Skip cropping if fail crop trail count exceeds this number. rand_pad_prob (float, optional, default=0) – Augmentation Param: Probability for random padding. max_pad_scale (float, optional, default=1) – Augmentation Param: Maximum padding scale. max_random_hue (int, optional, default='0') – Augmentation Param: Maximum random value of H channel in HSL color space. random_hue_prob (float, optional, default=0) – Augmentation Param: Probability to apply random hue. max_random_saturation (int, optional, default='0') – Augmentation Param: Maximum random value of S channel in HSL color space. random_saturation_prob (float, optional, default=0) – Augmentation Param: Probability to apply random saturation. max_random_illumination (int, optional, default='0') – Augmentation Param: Maximum random value of L channel in HSL color space. random_illumination_prob (float, optional, default=0) – Augmentation Param: Probability to apply random illumination. max_random_contrast (float, optional, default=0) – Augmentation Param: Maximum random value of delta contrast. random_contrast_prob (float, optional, default=0) – Augmentation Param: Probability to apply random contrast. rand_mirror_prob (float, optional, default=0) – Augmentation Param: Probability to apply horizontal flip aka. mirror. fill_value (int, optional, default='127') – Augmentation Param: Filled color value while padding. inter_method (int, optional, default='1') – Augmentation Param: 0-NN 1-bilinear 2-cubic 3-area 4-lanczos4 9-auto 10-rand. resize_mode ({'fit', 'force', 'shrink'},optional, default='force') – Augmentation Param: How image data fit in data_shape. force: force reshape to data_shape regardless of aspect ratio; shrink: ensure each side fit in data_shape, preserve aspect ratio; fit: fit image to data_shape, preserve ratio, will upscale if applicable. mean_img (string, optional, default='') – Augmentation Param: Mean Image to be subtracted. mean_r (float, optional, default=0) – Augmentation Param: Mean value on R channel. mean_g (float, optional, default=0) – Augmentation Param: Mean value on G channel. mean_b (float, optional, default=0) – Augmentation Param: Mean value on B channel. mean_a (float, optional, default=0) – Augmentation Param: Mean value on Alpha channel. std_r (float, optional, default=0) – Augmentation Param: Standard deviation on R channel. std_g (float, optional, default=0) – Augmentation Param: Standard deviation on G channel. std_b (float, optional, default=0) – Augmentation Param: Standard deviation on B channel. std_a (float, optional, default=0) – Augmentation Param: Standard deviation on Alpha channel. scale (float, optional, default=1) – Augmentation Param: Scale in color space.
Returns:	The result iterator.
Return type:	MXDataIter

mxnet.io.ImageRecordIter(*args, **kwargs)¶

Iterates on image RecordIO files

Reads batches of images from .rec RecordIO files. One can use im2rec.py tool (in tools/) to pack raw image files into RecordIO files. This iterator is less flexible to customization but is fast and has lot of language bindings. To iterate over raw images directly use ImageIter instead (in Python).

Example:

data_iter = mx.io.ImageRecordIter(
  path_imgrec="./sample.rec", # The target record file.
  data_shape=(3, 227, 227), # Output data shape; 227x227 region will be cropped from the original image.
  batch_size=4, # Number of items per batch.
  resize=256 # Resize the shorter edge to 256 before cropping.
  # You can specify more augmentation options. Use help(mx.io.ImageRecordIter) to see all the options.
  )
# You can now use the data_iter to access batches of images.
batch = data_iter.next() # first batch.
images = batch.data[0] # This will contain 4 (=batch_size) images each of 3x227x227.
# process the images
...
data_iter.reset() # To restart the iterator from the beginning.

Defined in src/io/iter_image_recordio_2.cc:L601

Parameters:	path_imglist (string, optional, default='') – Path to the image list (.lst) file. Generally created with tools/im2rec.py. Format (Tab separated): . path_imgrec (string, optional, default='') – Path to the image RecordIO (.rec) file or a directory path. Created with tools/im2rec.py. aug_seq (string, optional, default='aug_default') – The augmenter names to represent sequence of augmenters to be applied, seperated by comma. Additional keyword parameters will be seen by these augmenters. label_width (int, optional, default='1') – The number of labels per image. data_shape (Shape(tuple), required) – The shape of one output image in (channels, height, width) format. preprocess_threads (int, optional, default='4') – The number of threads to do preprocessing. verbose (boolean, optional, default=True) – If or not output verbose information. num_parts (int, optional, default='1') – Virtually partition the data into these many parts. part_index (int, optional, default='0') – The i-th virtual partition to be read. shuffle_chunk_size (long (non-negative), optional, default=0) – The data shuffle buffer size in MB. Only valid if shuffle is true. shuffle_chunk_seed (int, optional, default='0') – The random seed for shuffling shuffle (boolean, optional, default=False) – Whether to shuffle data randomly or not. seed (int, optional, default='0') – The random seed. batch_size (int (non-negative), required) – Batch size. round_batch (boolean, optional, default=True) – Whether to use round robin to handle overflow batch or not. prefetch_buffer (long (non-negative), optional, default=4) – Maximum number of batches to prefetch. dtype ({None, 'float16', 'float32', 'float64', 'int32', 'uint8'},optional, default='None') – Output data type. `None` means no change. resize (int, optional, default='-1') – Down scale the shorter edge to a new size before applying other augmentations. rand_crop (boolean, optional, default=False) – If or not randomly crop the image max_rotate_angle (int, optional, default='0') – Rotate by a random degree in `[-v, v]` max_aspect_ratio (float, optional, default=0) – Change the aspect (namely width/height) to a random value in `[1 - max_aspect_ratio, 1 + max_aspect_ratio]` max_shear_ratio (float, optional, default=0) – Apply a shear transformation (namely `(x,y)->(x+my,y)`) with `m` randomly chose from `[-max_shear_ratio, max_shear_ratio]` max_crop_size (int, optional, default='-1') – Crop both width and height into a random size in `[min_crop_size, max_crop_size]` min_crop_size (int, optional, default='-1') – Crop both width and height into a random size in `[min_crop_size, max_crop_size]` max_random_scale (float, optional, default=1) – Resize into `[widths, heights]` with `s` randomly chosen from `[min_random_scale, max_random_scale]` min_random_scale (float, optional, default=1) – Resize into `[widths, heights]` with `s` randomly chosen from `[min_random_scale, max_random_scale]` max_img_size (float, optional, default=1e+10) – Set the maximal width and height after all resize and rotate argumentation are applied min_img_size (float, optional, default=0) – Set the minimal width and height after all resize and rotate argumentation are applied random_h (int, optional, default='0') – Add a random value in `[-random_h, random_h]` to the H channel in HSL color space. random_s (int, optional, default='0') – Add a random value in `[-random_s, random_s]` to the S channel in HSL color space. random_l (int, optional, default='0') – Add a random value in `[-random_l, random_l]` to the L channel in HSL color space. rotate (int, optional, default='-1') – Rotate by an angle. If set, it overwrites the `max_rotate_angle` option. fill_value (int, optional, default='255') – Set the padding pixes value into `fill_value`. inter_method (int, optional, default='1') – The interpolation method: 0-NN 1-bilinear 2-cubic 3-area 4-lanczos4 9-auto 10-rand. pad (int, optional, default='0') – Change size from `[width, height]` into `[pad + width + pad, pad + height + pad]` by padding pixes mirror (boolean, optional, default=False) – Whether to mirror the image or not. If true, images are flipped along the horizontal axis. rand_mirror (boolean, optional, default=False) – Whether to randomly mirror images or not. If true, 50% of the images will be randomly mirrored (flipped along the horizontal axis) mean_img (string, optional, default='') – Filename of the mean image. mean_r (float, optional, default=0) – The mean value to be subtracted on the R channel mean_g (float, optional, default=0) – The mean value to be subtracted on the G channel mean_b (float, optional, default=0) – The mean value to be subtracted on the B channel mean_a (float, optional, default=0) – The mean value to be subtracted on the alpha channel scale (float, optional, default=1) – Multiply the image with a scale value. max_random_contrast (float, optional, default=0) – Change the contrast with a value randomly chosen from `[-max_random_contrast, max_random_contrast]` max_random_illumination (float, optional, default=0) – Change the illumination with a value randomly chosen from `[-max_random_illumination, max_random_illumination]`
Returns:	The result iterator.
Return type:	MXDataIter

mxnet.io.ImageRecordIter_v1(*args, **kwargs)¶

Iterating on image RecordIO files

Read images batches from RecordIO files with a rich of data augmentation options.

One can use tools/im2rec.py to pack individual image files into RecordIO files.

Defined in src/io/iter_image_recordio.cc:L346

Parameters:	path_imglist (string, optional, default='') – Path to the image list (.lst) file. Generally created with tools/im2rec.py. Format (Tab separated): . path_imgrec (string, optional, default='') – Path to the image RecordIO (.rec) file or a directory path. Created with tools/im2rec.py. aug_seq (string, optional, default='aug_default') – The augmenter names to represent sequence of augmenters to be applied, seperated by comma. Additional keyword parameters will be seen by these augmenters. label_width (int, optional, default='1') – The number of labels per image. data_shape (Shape(tuple), required) – The shape of one output image in (channels, height, width) format. preprocess_threads (int, optional, default='4') – The number of threads to do preprocessing. verbose (boolean, optional, default=True) – If or not output verbose information. num_parts (int, optional, default='1') – Virtually partition the data into these many parts. part_index (int, optional, default='0') – The i-th virtual partition to be read. shuffle_chunk_size (long (non-negative), optional, default=0) – The data shuffle buffer size in MB. Only valid if shuffle is true. shuffle_chunk_seed (int, optional, default='0') – The random seed for shuffling shuffle (boolean, optional, default=False) – Whether to shuffle data randomly or not. seed (int, optional, default='0') – The random seed. batch_size (int (non-negative), required) – Batch size. round_batch (boolean, optional, default=True) – Whether to use round robin to handle overflow batch or not. prefetch_buffer (long (non-negative), optional, default=4) – Maximum number of batches to prefetch. dtype ({None, 'float16', 'float32', 'float64', 'int32', 'uint8'},optional, default='None') – Output data type. `None` means no change. resize (int, optional, default='-1') – Down scale the shorter edge to a new size before applying other augmentations. rand_crop (boolean, optional, default=False) – If or not randomly crop the image max_rotate_angle (int, optional, default='0') – Rotate by a random degree in `[-v, v]` max_aspect_ratio (float, optional, default=0) – Change the aspect (namely width/height) to a random value in `[1 - max_aspect_ratio, 1 + max_aspect_ratio]` max_shear_ratio (float, optional, default=0) – Apply a shear transformation (namely `(x,y)->(x+my,y)`) with `m` randomly chose from `[-max_shear_ratio, max_shear_ratio]` max_crop_size (int, optional, default='-1') – Crop both width and height into a random size in `[min_crop_size, max_crop_size]` min_crop_size (int, optional, default='-1') – Crop both width and height into a random size in `[min_crop_size, max_crop_size]` max_random_scale (float, optional, default=1) – Resize into `[widths, heights]` with `s` randomly chosen from `[min_random_scale, max_random_scale]` min_random_scale (float, optional, default=1) – Resize into `[widths, heights]` with `s` randomly chosen from `[min_random_scale, max_random_scale]` max_img_size (float, optional, default=1e+10) – Set the maximal width and height after all resize and rotate argumentation are applied min_img_size (float, optional, default=0) – Set the minimal width and height after all resize and rotate argumentation are applied random_h (int, optional, default='0') – Add a random value in `[-random_h, random_h]` to the H channel in HSL color space. random_s (int, optional, default='0') – Add a random value in `[-random_s, random_s]` to the S channel in HSL color space. random_l (int, optional, default='0') – Add a random value in `[-random_l, random_l]` to the L channel in HSL color space. rotate (int, optional, default='-1') – Rotate by an angle. If set, it overwrites the `max_rotate_angle` option. fill_value (int, optional, default='255') – Set the padding pixes value into `fill_value`. inter_method (int, optional, default='1') – The interpolation method: 0-NN 1-bilinear 2-cubic 3-area 4-lanczos4 9-auto 10-rand. pad (int, optional, default='0') – Change size from `[width, height]` into `[pad + width + pad, pad + height + pad]` by padding pixes mirror (boolean, optional, default=False) – Whether to mirror the image or not. If true, images are flipped along the horizontal axis. rand_mirror (boolean, optional, default=False) – Whether to randomly mirror images or not. If true, 50% of the images will be randomly mirrored (flipped along the horizontal axis) mean_img (string, optional, default='') – Filename of the mean image. mean_r (float, optional, default=0) – The mean value to be subtracted on the R channel mean_g (float, optional, default=0) – The mean value to be subtracted on the G channel mean_b (float, optional, default=0) – The mean value to be subtracted on the B channel mean_a (float, optional, default=0) – The mean value to be subtracted on the alpha channel scale (float, optional, default=1) – Multiply the image with a scale value. max_random_contrast (float, optional, default=0) – Change the contrast with a value randomly chosen from `[-max_random_contrast, max_random_contrast]` max_random_illumination (float, optional, default=0) – Change the illumination with a value randomly chosen from `[-max_random_illumination, max_random_illumination]`
Returns:	The result iterator.
Return type:	MXDataIter

mxnet.io.ImageRecordUInt8Iter(*args, **kwargs)¶

Iterating on image RecordIO files

This iterator is identical to ImageRecordIter except for using uint8 as the data type instead of float.

Defined in src/io/iter_image_recordio_2.cc:L618

Parameters:	path_imglist (string, optional, default='') – Path to the image list (.lst) file. Generally created with tools/im2rec.py. Format (Tab separated): . path_imgrec (string, optional, default='') – Path to the image RecordIO (.rec) file or a directory path. Created with tools/im2rec.py. aug_seq (string, optional, default='aug_default') – The augmenter names to represent sequence of augmenters to be applied, seperated by comma. Additional keyword parameters will be seen by these augmenters. label_width (int, optional, default='1') – The number of labels per image. data_shape (Shape(tuple), required) – The shape of one output image in (channels, height, width) format. preprocess_threads (int, optional, default='4') – The number of threads to do preprocessing. verbose (boolean, optional, default=True) – If or not output verbose information. num_parts (int, optional, default='1') – Virtually partition the data into these many parts. part_index (int, optional, default='0') – The i-th virtual partition to be read. shuffle_chunk_size (long (non-negative), optional, default=0) – The data shuffle buffer size in MB. Only valid if shuffle is true. shuffle_chunk_seed (int, optional, default='0') – The random seed for shuffling shuffle (boolean, optional, default=False) – Whether to shuffle data randomly or not. seed (int, optional, default='0') – The random seed. batch_size (int (non-negative), required) – Batch size. round_batch (boolean, optional, default=True) – Whether to use round robin to handle overflow batch or not. prefetch_buffer (long (non-negative), optional, default=4) – Maximum number of batches to prefetch. dtype ({None, 'float16', 'float32', 'float64', 'int32', 'uint8'},optional, default='None') – Output data type. `None` means no change. resize (int, optional, default='-1') – Down scale the shorter edge to a new size before applying other augmentations. rand_crop (boolean, optional, default=False) – If or not randomly crop the image max_rotate_angle (int, optional, default='0') – Rotate by a random degree in `[-v, v]` max_aspect_ratio (float, optional, default=0) – Change the aspect (namely width/height) to a random value in `[1 - max_aspect_ratio, 1 + max_aspect_ratio]` max_shear_ratio (float, optional, default=0) – Apply a shear transformation (namely `(x,y)->(x+my,y)`) with `m` randomly chose from `[-max_shear_ratio, max_shear_ratio]` max_crop_size (int, optional, default='-1') – Crop both width and height into a random size in `[min_crop_size, max_crop_size]` min_crop_size (int, optional, default='-1') – Crop both width and height into a random size in `[min_crop_size, max_crop_size]` max_random_scale (float, optional, default=1) – Resize into `[widths, heights]` with `s` randomly chosen from `[min_random_scale, max_random_scale]` min_random_scale (float, optional, default=1) – Resize into `[widths, heights]` with `s` randomly chosen from `[min_random_scale, max_random_scale]` max_img_size (float, optional, default=1e+10) – Set the maximal width and height after all resize and rotate argumentation are applied min_img_size (float, optional, default=0) – Set the minimal width and height after all resize and rotate argumentation are applied random_h (int, optional, default='0') – Add a random value in `[-random_h, random_h]` to the H channel in HSL color space. random_s (int, optional, default='0') – Add a random value in `[-random_s, random_s]` to the S channel in HSL color space. random_l (int, optional, default='0') – Add a random value in `[-random_l, random_l]` to the L channel in HSL color space. rotate (int, optional, default='-1') – Rotate by an angle. If set, it overwrites the `max_rotate_angle` option. fill_value (int, optional, default='255') – Set the padding pixes value into `fill_value`. inter_method (int, optional, default='1') – The interpolation method: 0-NN 1-bilinear 2-cubic 3-area 4-lanczos4 9-auto 10-rand. pad (int, optional, default='0') – Change size from `[width, height]` into `[pad + width + pad, pad + height + pad]` by padding pixes
Returns:	The result iterator.
Return type:	MXDataIter

mxnet.io.ImageRecordUInt8Iter_v1(*args, **kwargs)¶

Iterating on image RecordIO files

This iterator is identical to ImageRecordIter except for using uint8 as the data type instead of float.

Defined in src/io/iter_image_recordio.cc:L367

Parameters:	path_imglist (string, optional, default='') – Path to the image list (.lst) file. Generally created with tools/im2rec.py. Format (Tab separated): . path_imgrec (string, optional, default='') – Path to the image RecordIO (.rec) file or a directory path. Created with tools/im2rec.py. aug_seq (string, optional, default='aug_default') – The augmenter names to represent sequence of augmenters to be applied, seperated by comma. Additional keyword parameters will be seen by these augmenters. label_width (int, optional, default='1') – The number of labels per image. data_shape (Shape(tuple), required) – The shape of one output image in (channels, height, width) format. preprocess_threads (int, optional, default='4') – The number of threads to do preprocessing. verbose (boolean, optional, default=True) – If or not output verbose information. num_parts (int, optional, default='1') – Virtually partition the data into these many parts. part_index (int, optional, default='0') – The i-th virtual partition to be read. shuffle_chunk_size (long (non-negative), optional, default=0) – The data shuffle buffer size in MB. Only valid if shuffle is true. shuffle_chunk_seed (int, optional, default='0') – The random seed for shuffling shuffle (boolean, optional, default=False) – Whether to shuffle data randomly or not. seed (int, optional, default='0') – The random seed. batch_size (int (non-negative), required) – Batch size. round_batch (boolean, optional, default=True) – Whether to use round robin to handle overflow batch or not. prefetch_buffer (long (non-negative), optional, default=4) – Maximum number of batches to prefetch. dtype ({None, 'float16', 'float32', 'float64', 'int32', 'uint8'},optional, default='None') – Output data type. `None` means no change. resize (int, optional, default='-1') – Down scale the shorter edge to a new size before applying other augmentations. rand_crop (boolean, optional, default=False) – If or not randomly crop the image max_rotate_angle (int, optional, default='0') – Rotate by a random degree in `[-v, v]` max_aspect_ratio (float, optional, default=0) – Change the aspect (namely width/height) to a random value in `[1 - max_aspect_ratio, 1 + max_aspect_ratio]` max_shear_ratio (float, optional, default=0) – Apply a shear transformation (namely `(x,y)->(x+my,y)`) with `m` randomly chose from `[-max_shear_ratio, max_shear_ratio]` max_crop_size (int, optional, default='-1') – Crop both width and height into a random size in `[min_crop_size, max_crop_size]` min_crop_size (int, optional, default='-1') – Crop both width and height into a random size in `[min_crop_size, max_crop_size]` max_random_scale (float, optional, default=1) – Resize into `[widths, heights]` with `s` randomly chosen from `[min_random_scale, max_random_scale]` min_random_scale (float, optional, default=1) – Resize into `[widths, heights]` with `s` randomly chosen from `[min_random_scale, max_random_scale]` max_img_size (float, optional, default=1e+10) – Set the maximal width and height after all resize and rotate argumentation are applied min_img_size (float, optional, default=0) – Set the minimal width and height after all resize and rotate argumentation are applied random_h (int, optional, default='0') – Add a random value in `[-random_h, random_h]` to the H channel in HSL color space. random_s (int, optional, default='0') – Add a random value in `[-random_s, random_s]` to the S channel in HSL color space. random_l (int, optional, default='0') – Add a random value in `[-random_l, random_l]` to the L channel in HSL color space. rotate (int, optional, default='-1') – Rotate by an angle. If set, it overwrites the `max_rotate_angle` option. fill_value (int, optional, default='255') – Set the padding pixes value into `fill_value`. inter_method (int, optional, default='1') – The interpolation method: 0-NN 1-bilinear 2-cubic 3-area 4-lanczos4 9-auto 10-rand. pad (int, optional, default='0') – Change size from `[width, height]` into `[pad + width + pad, pad + height + pad]` by padding pixes
Returns:	The result iterator.
Return type:	MXDataIter

mxnet.io.MNISTIter(*args, **kwargs)¶

Iterating on the MNIST dataset.

One can download the dataset from http://yann.lecun.com/exdb/mnist/

Defined in src/io/iter_mnist.cc:L264

Parameters:	image (string, optional, default='./train-images-idx3-ubyte') – Dataset Param: Mnist image path. label (string, optional, default='./train-labels-idx1-ubyte') – Dataset Param: Mnist label path. batch_size (int, optional, default='128') – Batch Param: Batch Size. shuffle (boolean, optional, default=True) – Augmentation Param: Whether to shuffle data. flat (boolean, optional, default=False) – Augmentation Param: Whether to flat the data into 1D. seed (int, optional, default='0') – Augmentation Param: Random Seed. silent (boolean, optional, default=False) – Auxiliary Param: Whether to print out data info. num_parts (int, optional, default='1') – partition the data into multiple parts part_index (int, optional, default='0') – the index of the part will read prefetch_buffer (long (non-negative), optional, default=4) – Maximum number of batches to prefetch. dtype ({None, 'float16', 'float32', 'float64', 'int32', 'uint8'},optional, default='None') – Output data type. `None` means no change.
Returns:	The result iterator.
Return type:	MXDataIter

Read and write for the RecordIO data format.

class mxnet.recordio.MXRecordIO(uri, flag)[source]¶

Reads/writes RecordIO data format, supporting sequential read and write.

>>> record = mx.recordio.MXRecordIO('tmp.rec', 'w')

>>> for i in range(5):
...    record.write('record_%d'%i)
>>> record.close()
>>> record = mx.recordio.MXRecordIO('tmp.rec', 'r')
>>> for i in range(5):
...    item = record.read()
...    print(item)
record_0
record_1
record_2
record_3
record_4
>>> record.close()

Parameters:	uri (string) – Path to the record file. flag (string) – ‘w’ for write or ‘r’ for read.

open()[source]¶: Opens the record file.

close()[source]¶: Closes the record file.

reset()[source]¶

Resets the pointer to first item.

If the record is opened with ‘w’, this function will truncate the file to empty.

>>> record = mx.recordio.MXRecordIO('tmp.rec', 'r')
>>> for i in range(2):
...    item = record.read()
...    print(item)
record_0
record_1
>>> record.reset()  # Pointer is reset.
>>> print(record.read()) # Started reading from start again.
record_0
>>> record.close()

write(buf)[source]¶

Inserts a string buffer as a record.

>>> record = mx.recordio.MXRecordIO('tmp.rec', 'w')
>>> for i in range(5):
...    record.write('record_%d'%i)
>>> record.close()

Parameters:	buf (string (python2), bytes (python3)) – Buffer to write.

read()[source]¶

Returns record as a string.

>>> record = mx.recordio.MXRecordIO('tmp.rec', 'r')
>>> for i in range(5):
...    item = record.read()
...    print(item)
record_0
record_1
record_2
record_3
record_4
>>> record.close()

Returns:	buf – Buffer read.
Return type:	string

class mxnet.recordio.MXIndexedRecordIO(idx_path, uri, flag, key_type=)[source]¶

Reads/writes RecordIO data format, supporting random access.

>>> for i in range(5):
...     record.write_idx(i, 'record_%d'%i)
>>> record.close()
>>> record = mx.recordio.MXIndexedRecordIO('tmp.idx', 'tmp.rec', 'r')
>>> record.read_idx(3)
record_3

Parameters:	idx_path (str) – Path to the index file. uri (str) – Path to the record file. Only supports seekable file types. flag (str) – ‘w’ for write or ‘r’ for read. key_type (type) – Data type for keys.

close()[source]¶: Closes the record file.

seek(idx)[source]¶

Sets the current read pointer position.

This function is internally called by read_idx(idx) to find the current reader pointer position. It doesn’t return anything.

tell()[source]¶

Returns the current position of write head.

>>> record = mx.recordio.MXIndexedRecordIO('tmp.idx', 'tmp.rec', 'w')
>>> print(record.tell())
0
>>> for i in range(5):
...     record.write_idx(i, 'record_%d'%i)
...     print(record.tell())
16
32
48
64
80

read_idx(idx)[source]¶

Returns the record at given index.

>>> record = mx.recordio.MXIndexedRecordIO('tmp.idx', 'tmp.rec', 'w')
>>> for i in range(5):
...     record.write_idx(i, 'record_%d'%i)
>>> record.close()
>>> record = mx.recordio.MXIndexedRecordIO('tmp.idx', 'tmp.rec', 'r')
>>> record.read_idx(3)
record_3

write_idx(idx, buf)[source]¶

Inserts input record at given index.

>>> for i in range(5):
...     record.write_idx(i, 'record_%d'%i)
>>> record.close()

Parameters:	idx (int) – Index of a file. buf – Record to write.

mxnet.recordio.IRHeader¶

An alias for HEADER. Used to store metadata (e.g. labels) accompanying a record. See mxnet.recordio.pack and mxnet.recordio.pack_img for example uses.

Parameters:	flag (int) – Available for convenience, can be set arbitrarily. label (float or an array of float) – Typically used to store label(s) for a record. id (int) – Usually a unique id representing record. id2 (int) – Higher order bits of the unique id, should be set to 0 (in most cases).

alias of HEADER

mxnet.recordio.pack(header, s)[source]¶

Pack a string into MXImageRecord.

Parameters:	header (IRHeader) – Header of the image record. `header.label` can be a number or an array. See more detail in `IRHeader`. s (str) – Raw image string to be packed.
Returns:	s – The packed string.
Return type:	str

Examples

>>> label = 4 # label can also be a 1-D array, for example: label = [1,2,3]
>>> id = 2574
>>> header = mx.recordio.IRHeader(0, label, id, 0)
>>> with open(path, 'r') as file:
...     s = file.read()
>>> packed_s = mx.recordio.pack(header, s)

mxnet.recordio.unpack(s)[source]¶

Unpack a MXImageRecord to string.

Parameters:	s (str) – String buffer from `MXRecordIO.read`.
Returns:	header (IRHeader) – Header of the image record. s (str) – Unpacked string.

Examples

>>> record = mx.recordio.MXRecordIO('test.rec', 'r')
>>> item = record.read()
>>> header, s = mx.recordio.unpack(item)
>>> header
HEADER(flag=0, label=14.0, id=20129312, id2=0)

mxnet.recordio.unpack_img(s, iscolor=-1)[source]¶

Unpack a MXImageRecord to image.

Parameters:

s (str) – String buffer from MXRecordIO.read.
iscolor (int) – Image format option for cv2.imdecode.

Returns:

header (IRHeader) – Header of the image record.
img (numpy.ndarray) – Unpacked image.

Examples

>>> record = mx.recordio.MXRecordIO('test.rec', 'r')
>>> item = record.read()
>>> header, img = mx.recordio.unpack_img(item)
>>> header
HEADER(flag=0, label=14.0, id=20129312, id2=0)
>>> img
array([[[ 23,  27,  45],
        [ 28,  32,  50],
        ...,
        [ 36,  40,  59],
        [ 35,  39,  58]],
       ...,
       [[ 91,  92, 113],
        [ 97,  98, 119],
        ...,
        [168, 169, 167],
        [166, 167, 165]]], dtype=uint8)

mxnet.recordio.pack_img(header, img, quality=95, img_fmt='.jpg')[source]¶

Pack an image into MXImageRecord.

Parameters:	header (IRHeader) – Header of the image record. `header.label` can be a number or an array. See more detail in `IRHeader`. img (numpy.ndarray) – Image to be packed. quality (int) – Quality for JPEG encoding in range 1-100, or compression for PNG encoding in range 1-9. img_fmt (str) – Encoding of the image (.jpg for JPEG, .png for PNG).
Returns:	s – The packed string.
Return type:	str

Examples

>>> label = 4 # label can also be a 1-D array, for example: label = [1,2,3]
>>> id = 2574
>>> header = mx.recordio.IRHeader(0, label, id, 0)
>>> img = cv2.imread('test.jpg')
>>> packed_s = mx.recordio.pack_img(header, img)

Returns:	The data of next batch.
Return type:	DataBatch
Raises:	`StopIteration` – If the end of the data is reached.

Returns:	The data of the current batch.
Return type:	list of NDArray

Returns:	The label of the current batch.
Return type:	list of NDArray

Returns:	index – The indices of examples in the current batch.
Return type:	numpy.array

Returns:	Number of padding examples in the current batch.
Return type:	int