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Inference and evaluation on the Open Images dataset

This page presents a tutorial for running object detector inference and evaluation measure computations on the Open Images dataset, using tools from the TensorFlow Object Detection API. It shows how to download the images and annotations for the validation and test sets of Open Images; how to package the downloaded data in a format understood by the Object Detection API; where to find a trained object detector model for Open Images; how to run inference; and how to compute evaluation measures on the inferred detections.

Inferred detections will look like the following:

On the validation set of Open Images, this tutorial requires 27GB of free disk space and the inference step takes approximately 9 hours on a single NVIDIA Tesla P100 GPU. On the test set -- 75GB and 27 hours respectively. All other steps require less than two hours in total on both sets.

Installing TensorFlow, the Object Detection API, and Google Cloud SDK

Please run through the installation instructions to install TensorFlow and all its dependencies. Ensure the Protobuf libraries are compiled and the library directories are added to PYTHONPATH. You will also need to pip install pandas and contextlib2.

Some of the data used in this tutorial lives in Google Cloud buckets. To access it, you will have to install the Google Cloud SDK on your workstation or laptop.

Preparing the Open Images validation and test sets

In order to run inference and subsequent evaluation measure computations, we require a dataset of images and ground truth boxes, packaged as TFRecords of TFExamples. To create such a dataset for Open Images, you will need to first download ground truth boxes from the Open Images website:

# From tensorflow/models/research
mkdir oid
cd oid
wget https://storage.googleapis.com/openimages/2017_07/annotations_human_bbox_2017_07.tar.gz
tar -xvf annotations_human_bbox_2017_07.tar.gz

Next, download the images. In this tutorial, we will use lower resolution images provided by CVDF. Please follow the instructions on CVDF's Open Images repository page in order to gain access to the cloud bucket with the images. Then run:

# From tensorflow/models/research/oid
SPLIT=validation  # Set SPLIT to "test" to download the images in the test set
mkdir raw_images_${SPLIT}
gsutil -m rsync -r gs://open-images-dataset/$SPLIT raw_images_${SPLIT}

Another option for downloading the images is to follow the URLs contained in the image URLs and metadata CSV files on the Open Images website.

At this point, your tensorflow/models/research/oid directory should appear as follows:

|-- 2017_07
|   |-- test
|   |   `-- annotations-human-bbox.csv
|   |-- train
|   |   `-- annotations-human-bbox.csv
|   `-- validation
|       `-- annotations-human-bbox.csv
|-- raw_images_validation (if you downloaded the validation split)
|   `-- ... (41,620 files matching regex "[0-9a-f]{16}.jpg")
|-- raw_images_test (if you downloaded the test split)
|   `-- ... (125,436 files matching regex "[0-9a-f]{16}.jpg")
`-- annotations_human_bbox_2017_07.tar.gz

Next, package the data into TFRecords of TFExamples by running:

# From tensorflow/models/research/oid
SPLIT=validation  # Set SPLIT to "test" to create TFRecords for the test split
mkdir ${SPLIT}_tfrecords

PYTHONPATH=$PYTHONPATH:$(readlink -f ..) \
python -m object_detection/dataset_tools/create_oid_tf_record \
  --input_box_annotations_csv 2017_07/$SPLIT/annotations-human-bbox.csv \
  --input_images_directory raw_images_${SPLIT} \
  --input_label_map ../object_detection/data/oid_bbox_trainable_label_map.pbtxt \
  --output_tf_record_path_prefix ${SPLIT}_tfrecords/$SPLIT.tfrecord \
  --num_shards=100

To add image-level labels, use the --input_image_label_annotations_csv flag.

This results in 100 TFRecord files (shards), written to oid/${SPLIT}_tfrecords, with filenames matching ${SPLIT}.tfrecord-000[0-9][0-9]-of-00100. Each shard contains approximately the same number of images and is defacto a representative random sample of the input data. This enables a straightforward work division scheme for distributing inference and also approximate measure computations on subsets of the validation and test sets.

Inferring detections

Inference requires a trained object detection model. In this tutorial we will use a model from the detections model zoo, which can be downloaded and unpacked by running the commands below. More information about the model, such as its architecture and how it was trained, is available in the model zoo page.

# From tensorflow/models/research/oid
wget http://download.tensorflow.org/models/object_detection/faster_rcnn_inception_resnet_v2_atrous_oid_14_10_2017.tar.gz
tar -zxvf faster_rcnn_inception_resnet_v2_atrous_oid_14_10_2017.tar.gz

At this point, data is packed into TFRecords and we have an object detector model. We can run inference using:

# From tensorflow/models/research/oid
SPLIT=validation  # or test
TF_RECORD_FILES=$(ls -1 ${SPLIT}_tfrecords/* | tr '\n' ',')

PYTHONPATH=$PYTHONPATH:$(readlink -f ..) \
python -m object_detection/inference/infer_detections \
  --input_tfrecord_paths=$TF_RECORD_FILES \
  --output_tfrecord_path=${SPLIT}_detections.tfrecord-00000-of-00001 \
  --inference_graph=faster_rcnn_inception_resnet_v2_atrous_oid/frozen_inference_graph.pb \
  --discard_image_pixels

Inference preserves all fields of the input TFExamples, and adds new fields to store the inferred detections. This allows computing evaluation measures on the output TFRecord alone, as ground truth boxes are preserved as well. Since measure computations don't require access to the images, infer_detections can optionally discard them with the --discard_image_pixels flag. Discarding the images drastically reduces the size of the output TFRecord.

Accelerating inference

Running inference on the whole validation or test set can take a long time to complete due to the large number of images present in these sets (41,620 and 125,436 respectively). For quick but approximate evaluation, inference and the subsequent measure computations can be run on a small number of shards. To run for example on 2% of all the data, it is enough to set TF_RECORD_FILES as shown below before running infer_detections:

TF_RECORD_FILES=$(ls ${SPLIT}_tfrecords/${SPLIT}.tfrecord-0000[0-1]-of-00100 | tr '\n' ',')

Please note that computing evaluation measures on a small subset of the data introduces variance and bias, since some classes of objects won't be seen during evaluation. In the example above, this leads to 13.2% higher mAP on the first two shards of the validation set compared to the mAP for the full set (see mAP results).

Another way to accelerate inference is to run it in parallel on multiple TensorFlow devices on possibly multiple machines. The script below uses tmux to run a separate infer_detections process for each GPU on different partition of the input data.

# From tensorflow/models/research/oid
SPLIT=validation  # or test
NUM_GPUS=4
NUM_SHARDS=100

tmux new-session -d -s "inference"
function tmux_start { tmux new-window -d -n "inference:GPU$1" "${*:2}; exec bash"; }
for gpu_index in $(seq 0 $(($NUM_GPUS-1))); do
  start_shard=$(( $gpu_index * $NUM_SHARDS / $NUM_GPUS ))
  end_shard=$(( ($gpu_index + 1) * $NUM_SHARDS / $NUM_GPUS - 1))
  TF_RECORD_FILES=$(seq -s, -f "${SPLIT}_tfrecords/${SPLIT}.tfrecord-%05.0f-of-$(printf '%05d' $NUM_SHARDS)" $start_shard $end_shard)
  tmux_start ${gpu_index} \
  PYTHONPATH=$PYTHONPATH:$(readlink -f ..) CUDA_VISIBLE_DEVICES=$gpu_index \
  python -m object_detection/inference/infer_detections \
    --input_tfrecord_paths=$TF_RECORD_FILES \
    --output_tfrecord_path=${SPLIT}_detections.tfrecord-$(printf "%05d" $gpu_index)-of-$(printf "%05d" $NUM_GPUS) \
    --inference_graph=faster_rcnn_inception_resnet_v2_atrous_oid/frozen_inference_graph.pb \
    --discard_image_pixels
done

After all infer_detections processes finish, tensorflow/models/research/oid will contain one output TFRecord from each process, with name matching validation_detections.tfrecord-0000[0-3]-of-00004.

Computing evaluation measures

To compute evaluation measures on the inferred detections you first need to create the appropriate configuration files:

# From tensorflow/models/research/oid
SPLIT=validation  # or test
NUM_SHARDS=1  # Set to NUM_GPUS if using the parallel evaluation script above

mkdir -p ${SPLIT}_eval_metrics

echo "
label_map_path: '../object_detection/data/oid_bbox_trainable_label_map.pbtxt'
tf_record_input_reader: { input_path: '${SPLIT}_detections.tfrecord@${NUM_SHARDS}' }
" > ${SPLIT}_eval_metrics/${SPLIT}_input_config.pbtxt

echo "
metrics_set: 'oid_V2_detection_metrics'
" > ${SPLIT}_eval_metrics/${SPLIT}_eval_config.pbtxt

And then run:

# From tensorflow/models/research/oid
SPLIT=validation  # or test

PYTHONPATH=$PYTHONPATH:$(readlink -f ..) \
python -m object_detection/metrics/offline_eval_map_corloc \
  --eval_dir=${SPLIT}_eval_metrics \
  --eval_config_path=${SPLIT}_eval_metrics/${SPLIT}_eval_config.pbtxt \
  --input_config_path=${SPLIT}_eval_metrics/${SPLIT}_input_config.pbtxt

The first configuration file contains an object_detection.protos.InputReader message that describes the location of the necessary input files. The second file contains an object_detection.protos.EvalConfig message that describes the evaluation metric. For more information about these protos see the corresponding source files.

Expected mAPs

The result of running offline_eval_map_corloc is a CSV file located at ${SPLIT}_eval_metrics/metrics.csv. With the above configuration, the file will contain average precision at IoU≥0.5 for each of the classes present in the dataset. It will also contain the mAP@IoU≥0.5. Both the per-class average precisions and the mAP are computed according to the Open Images evaluation protocol. The expected mAPs for the validation and test sets of Open Images in this case are:

Set Fraction of data Images mAP@IoU≥0.5
validation everything 41,620 39.2%
validation first 2 shards 884 52.4%
test everything 125,436 37.7%
test first 2 shards 2,476 50.8%