Data loading: MXNet recordIO¶
This example shows you how to use the data that is stored in the MXNet recordIO format with DALI.
Creating an Index¶
To use data that is stored in the recordIO format, we need to use the
MXNetReader operator. In addition to the arguments that are common to all readers, such as
random_shuffle, this operator takes the
pathis the list of paths to recordIO files
index_pathis a list (of size 1) that contains the path to the index file. This file, with
.idxextension, is automatically created when you use MXNet’s
im2rec.pyutility; and can also be obtained from the recordIO file by using the
rec2idxutility that is included with DALI.
DALI_EXTRA_PATH environment variable should point to the location where data from DALI extra repository is downloaded.
Important: Ensure that you check out the correct release tag that corresponds to the installed version of DALI.
from nvidia.dali.pipeline import Pipeline import nvidia.dali.fn as fn import nvidia.dali.types as types import numpy as np import os.path test_data_root = os.environ['DALI_EXTRA_PATH'] base = os.path.join(test_data_root, 'db', 'recordio') batch_size = 16 idx_files = [base + "/train.idx"] rec_files = [base + "/train.rec"]
Defining and running the pipeline¶
Define a simple pipeline that takes the images that are stored in the recordIO format, decodes them and prepares them for ingestion in DL framework.
Processing images involves cropping, normalizing, and
CHW conversion process.
pipe = Pipeline(batch_size=batch_size, num_threads=4, device_id=0) with pipe: jpegs, labels = fn.mxnet_reader(path=rec_files, index_path=idx_files) images = fn.image_decoder(jpegs, device="mixed", output_type=types.RGB) output = fn.crop_mirror_normalize( images, dtype=types.FLOAT, crop=(224, 224), mean=[0., 0., 0.], std=[1., 1., 1.]) pipe.set_outputs(output, labels)
Let us now build and run the pipeline:
pipe.build() pipe_out = pipe.run()
To visualize the results, use the
matplotliblibrary, which expects images in
HWCformat, but the output of the pipeline is in
CHW is the preferred format for most Deep Learning frameworks.
For the visualization purposes, transpose the images back to the
import matplotlib.gridspec as gridspec import matplotlib.pyplot as plt %matplotlib inline def show_images(image_batch): columns = 4 rows = (batch_size + 1) // (columns) fig = plt.figure(figsize = (32,(32 // columns) * rows)) gs = gridspec.GridSpec(rows, columns) for j in range(rows*columns): plt.subplot(gs[j]) plt.axis("off") img_chw = image_batch.at(j) img_hwc = np.transpose(img_chw, (1,2,0))/255.0 plt.imshow(img_hwc)
images, labels = pipe_out show_images(images.as_cpu())