PySpacer

PySpacer (AKA spacer) provides utilities to extract features from random point locations in images and then train classifiers over those features. It is used in the vision backend of https://github.com/coralnet/coralnet.

Spacer currently supports Python 3.10 and 3.11.

Installation

The spacer repo can be installed in three ways.

• Pip install -- for integration with other Python projects.
• Local clone -- ideal for testing and development.
• From Dockerfile -- the only option that supports Caffe, which is used for the legacy feature-extractor.

Config

Setting spacer config variables is only necessary when using certain features. If you don't need S3 storage, and you won't load extractors remotely, you can skip this section.

See CONFIGURABLE_VARS in config.py for a full list of available variables, and for an explanation of when each variable must be configured or not.

Spacer's config variables can be set in any of the following ways:

1. As environment variables; recommended if you pip install the package. Each variable name must be prefixed with SPACER_:
   • export SPACER_AWS_ACCESS_KEY_ID='YOUR_AWS_KEY_ID'
   • export SPACER_AWS_SECRET_ACCESS_KEY='YOUR_AWS_SECRET_KEY'
   • export SPACER_AWS_REGION='us-west-2'
   • export SPACER_EXTRACTORS_CACHE_DIR='/your/cache'
2. In a secrets.json file in the same directory as this README; recommended for Docker builds and local clones. Example secrets.json contents:

   {
     "AWS_ACCESS_KEY_ID": "YOUR_AWS_KEY_ID",
     "AWS_SECRET_ACCESS_KEY": "YOUR_AWS_SECRET_KEY",
     "AWS_REGION": "us-west-2",
     "EXTRACTORS_CACHE_DIR": "/your/cache"
   }
   

3. As a Django setting; recommended for a Django project that uses spacer. Example code in a Django settings module:

   SPACER = {
       'AWS_ACCESS_KEY_ID': 'YOUR_AWS_KEY_ID',
       'AWS_SECRET_ACCESS_KEY': 'YOUR_AWS_SECRET_KEY',
       'AWS_REGION': 'us-west-2',
       'EXTRACTORS_CACHE_DIR': '/your/cache',
   }
   

Spacer supports the following schemes of using multiple settings sources:

• Check environment variables first, then use secrets.json as a fallback.
• Check environment variables first, then use Django settings as a fallback.

However, spacer will not read from multiple file-based settings sources; so if a secrets.json file is present, then spacer will not check for Django settings as a fallback.

To debug your configuration, try opening a Python shell and run from spacer import config, then config.check().

Docker build

The docker build is used in coralnet's deployment.

• Install docker on your system
• Clone this repo to a local folder; let's say it's /your/local/pyspacer
• Set up configuration as detailed above.
• Choose a local folder for caching extractor files; let's say it's /your/local/cache
• Build image: docker build -f /your/local/pyspacer/Dockerfile -t myimagename
• Run: docker run -v /your/local/cache:/workspace/cache -v /your/local/pyspacer:/workspace/spacer -it myimagename
  • The -v /your/local/cache:/workspace/cache part ensures that all build attempts use the same cache folder of your host storage.
  • The -v /your/local/pyspacer:/workspace/spacer mounts your local spacer clone (including secrets.json, if used) so that the container has the right permissions.
  • Overall, this runs the default CMD command specified in the dockerfile (unit-test with coverage). If you want to enter the docker container, run the same command but append bash in the end.

Pip install

• pip install pyspacer
• Set up configuration. secrets.json isn't an option here, so either use environment variables, or Django settings if you have a Django project.

Local clone

• Clone this repo
  • If using Windows: turn Git's autocrlf setting off before your initial checkout. Otherwise, pickled classifiers in spacer/tests/fixtures will get checked out with \r\n newlines, and the pickle module will fail to load them, leading to test failures. However, autocrlf should be left on when adding any new non-pickle files.
• pip install -r requirements/dev.txt
• Set up configuration

Code overview

Spacer executes tasks as defined in messages. The message types are defined in messages.py and the tasks in tasks.py. Several data types which can be used for input and output serialization are defined in data_classes.py.

For examples on how to create spacer tasks, refer to the Core API section below, and the unit tests in test_tasks.py.

Tasks can be executed directly by calling the methods in tasks.py. However, spacer also supports an interface with AWS Batch handled by env_job() in mailman.py.

Spacer supports four storage types: s3, filesystem, memory and url. Refer to storage.py for details. The memory storage is mostly used for testing, and the url storage is read only.

config.py defines configurable variables/settings and various constants.

Core API

The tasks.py module has four functions which comprise the main interface of pyspacer:

extract_features

The first step when analyzing an image, or preparing an image as training data, is extracting features from the image. For this step, you specify a set of points (pixel locations) in the image which you want to analyze. At each point, spacer will crop a square of pixels centered around that location and extract features based on that square.

You'll also need a feature extractor, but spacer does not provide one out of the box. Spacer's extract_features.py provides the Python classes EfficientNetExtractor for loading EfficientNet extractors in PyTorch format (CoralNet 1.0's default extraction scheme), and VGG16CaffeExtractor for loading VGG16 extractors in Caffe format (CoralNet's legacy extraction scheme).

You'll either want to match one of these schemes so you can use the provided classes, or you'll have to write your own extractor class which inherits from the base class FeatureExtractor. Between the provided classes, the easier one to use will probably be EfficientNetExtractor, because Caffe is old software which is more complicated to install.

If you're loading the extractor files remotely (from S3 or from a URL), the files will be automatically cached to your configured EXTRACTORS_CACHE_DIR for faster subsequent loads.

The output of extract_features() is a single feature-vector file, which is a JSON file that is deserializable using the data_classes.ImageFeatures class. Example usage:

from spacer.extract_features import EfficientNetExtractor
from spacer.messages import DataLocation, ExtractFeaturesMsg
from spacer.tasks import extract_features

message = ExtractFeaturesMsg(
    # This token is purely for your bookkeeping; you may find it useful if you
    # choose to track tasks by saving these task messages. For example, you
    # can make the token something that uniquely identifies the input image.
    job_token='image1',
    # Instantiated feature extractor. Each extractor class defines the
    # data_locations which must be specified. In EfficientNetExtractor's case,
    # a PyTorch 'weights' file is required.
    extractor=EfficientNetExtractor(
        data_locations=dict(
            weights=DataLocation('filesystem', '/path/to/weights.pt'),
        ),
    ),
    # (row, column) tuples specifying pixel locations in the image.
    # Note that row is y, column is x.
    rowcols=[(2200, 1000), (1400, 1500), (3000, 450)],
    # Where the input image should be read from.
    image_loc=DataLocation('filesystem', '/path/to/image1.jpg'),
    # Where the feature vector should be output to.
    # CoralNet uses a custom .featurevector extension for these, but the
    # format is just JSON.
    feature_loc=DataLocation('filesystem', '/path/to/image1.featurevector'),
)
return_message = extract_features(message)
print("Feature vector stored at: /path/to/image1.featurevector")
print(f"Extraction runtime: {return_message.runtime:.1f} s")

train_classifier

To train a classifier, you need:

• Feature vectors; each vector corresponds to a set of point locations in one image
• Ground-truth labels (typically applied/confirmed by human inspection) for each of the points specified in those feature vectors
• Training parameters

The labels must be split into training, reference, and validation sets:

• The training set (train) is the data that actually goes into the classifier training algorithm during each training epoch. This is generally much larger than the other two sets.
• The reference set (ref) is used to evaluate and calibrate the classifier between epochs.
• The validation set (val) is used to evaluate the final classifier after training is finished.

This three-set split is known by other names elsewhere, such as training, validation, and test sets respectively, or training, development, and test sets respectively.

There are a few ways to create the labels structure. Each way involves creating one or more instances of data_classes.ImageLabels:

from spacer.data_classes import ImageLabels
image_labels = ImageLabels({
    # Labels for one feature vector's points.
    '/path/to/image1.featurevector': [
        # Point location at row 1000, column 2000, labeled as class 1.
        (1000, 2000, 1), 
        # Point location at row 3000, column 2000, labeled as class 2.
        (3000, 2000, 2),
    ],
    # Labels for another feature vector's points.
    '/path/to/image2.featurevector': [
        (1500, 2500, 3),
        (2500, 500, 1),
    ],
})

The labels argument of TrainClassifierMsg expects an instance of data_classes.TrainingTaskLabels. There are a few ways to create this:

1. Pass a single ImageLabels instance to the task_utils.preprocess_labels() function. preprocess_labels() will:
   • Split up your labels into train, ref, and val sets; optional arguments are available to control how the split is done.
   • Do error checks.
   • Optionally filter out unwanted classes, if you specified the accepted_classes argument.
   • Return a TrainingTaskLabels instance.
2. Create your own TrainingTaskLabels instance by passing three ImageLabels instances into the constructor: one ImageLabels for each of train, ref, and val. This lets you define your own arbitrary train/ref/val split.
3. Do method 2, but then pass your TrainingTaskLabels instance through preprocess_labels(). This allows you to use just the error-checking and class-filtering parts of preprocess_labels().

from spacer.data_classes import ImageLabels
from spacer.messages import TrainingTaskLabels
from spacer.task_utils import preprocess_labels

# 1
labels = preprocess_labels(
    ImageLabels("see previous code block for example args to ImageLabels..."),
    "optional args to preprocess_labels()...",
)
# 2
labels = TrainingTaskLabels(
    train=ImageLabels(...),
    ref=ImageLabels(...),
    val=ImageLabels(...),
)
# 3
labels = preprocess_labels(
    TrainingTaskLabels("args like the previous example..."),
    "optional args to preprocess_labels()...",
)

Once you have a TrainingTaskLabels instance, pass that and the other required arguments to TrainClassifierMsg, and then pass that message to train_classifier(), which produces:

• A classifier as an sklearn.calibration.CalibratedClassifierCV instance, stored in a pickle (.pkl) file. spacer's storage.load_classifier() function can help with loading classifiers that were created in older scikit-learn versions.
• Classifier evaluation results as a JSON file.

Example:

from spacer.data_classes import ImageLabels
from spacer.messages import DataLocation, TrainClassifierMsg
from spacer.tasks import train_classifier
from spacer.task_utils import preprocess_labels

message = TrainClassifierMsg(
    # For your bookkeeping.
    job_token='classifier1',
    # 'minibatch' is currently the only trainer that spacer defines.
    trainer_name='minibatch',
    # How many iterations the training algorithm should run; more epochs
    # = more opportunity to converge to a better fit, but slower.
    nbr_epochs=10,
    # Classifier types available:
    # 1. 'MLP': multi-layer perceptron; newer classifier type for CoralNet
    # 2. 'LR': logistic regression; older classifier type for CoralNet
    # Both types are run with scikit-learn.
    clf_type='MLP',
    # Point-locations to ground-truth-labels (annotations) mappings
    # used to train the classifier.
    # The dict keys must be the same as the `key` used in the
    # extract-features task's `feature_loc`.
    # The dict values are lists of tuples of (row, column, label ID).
    # Label IDs may be either integers or strings.
    # preprocess_labels() can automatically split the data into training,
    # reference, and validation sets. However, you may also define how to
    # split it yourself; for details, see `TrainingTaskLabels` comments
    # in messages.py.
    labels=preprocess_labels(ImageLabels({
        '/path/to/image1.featurevector': [(1000, 2000, 1), (3000, 2000, 2)],
        '/path/to/image2.featurevector': [(1000, 2000, 3), (3000, 2000, 1)],
        '/path/to/image3.featurevector': [(1234, 2857, 11), (3094, 2262, 25)],
    })),
    # All the feature vectors should use the same storage_type, and the same
    # S3 bucket_name if applicable. This DataLocation's purpose is to describe
    # those common storage details. The key arg is ignored, because that will
    # be different for each feature vector.
    features_loc=DataLocation('filesystem', ''),
    # List of previously-created models (classifiers) to also evaluate
    # using this validation set, for informational purposes only.
    # This can be handy for comparing classifiers.
    previous_model_locs=[
        DataLocation('filesystem', '/path/to/oldclassifier1.pkl'),
        DataLocation('filesystem', '/path/to/oldclassifier2.pkl'),
    ],
    # Where the new model (classifier) should be output to.
    model_loc=DataLocation('filesystem', '/path/to/classifier1.pkl'),
    # Where the detailed evaluation results of the new model should be stored.
    valresult_loc=DataLocation('filesystem', '/path/to/valresult.json'),
    # If feature vectors are loaded from remote storage, this specifies
    # where the feature-vector cache (a temporary directory in the local
    # filesystem) is located. Can be:
    # - The special value FeatureCache.AUTO, which lets the OS decide where
    #   the temporary directory lives. (Default)
    # - The special value FeatureCache.DISABLED, which makes feature
    #   vectors get loaded remotely every time without being cached
    #   (which means most vectors will be remote-loaded once per epoch).
    #   This would be desired if there isn't enough disk space to cache all
    #   features.
    # - Absolute path to the directory where the cache will live, either
    #   as a str or a pathlib.Path.
    feature_cache_dir=TrainClassifierMsg.FeatureCache.AUTO,
)
return_message = train_classifier(message)
print("Classifier stored at: /path/to/classifier1.pkl")
print("Evaluation results stored at: /path/to/valresult.json")
print(f"New model's accuracy (0.0 = 0%, 1.0 = 100%): {return_message.acc}")
print(
    f"Previous models' accuracies on the validation set:"
    f" {return_message.pc_accs}")
print(
    "New model's accuracy progression (calculated on the reference set)"
    f" after each epoch of training: {return_message.ref_accs}")
print(f"Training runtime: {return_message.runtime:.1f} s")

Evaluation results consist of three arrays:

• gt: Ground-truth label IDs for each point in the validation set.
• est: Estimated (classifier-predicted) label IDs for each point in the validation set.
• scores: Classifier's confidence scores (0.0 = 0%, 1.0 = 100%) for each estimated label ID.

The ith element of gt, ith element of est, and ith element of scores correspond to each other. But the elements are otherwise in an undefined order.

Accuracy is defined as the percentage of gt labels that match the corresponding est labels.

Here's a snippet which lists out the evaluation results:

import json
from spacer.data_classes import ValResults
with open('/path/to/valresult.json') as f:
    valresult = ValResults.deserialize(json.load(f))
for ground_truth_i, prediction_i, score in zip(
    valresult.gt, valresult.est, valresult.scores
):
    print(
        f"Actual = {valresult.classes[ground_truth_i]},"
        f" Predicted = {valresult.classes[prediction_i]},"
        f" Confidence = {100*score:.1f}%")

classify_features

Takes a feature vector (representing points in an image) to classify, and a classifier trained on the same type of features (EfficientNet or VGG16). Produces prediction results (scores) for the image points, as posterior probabilities for each class. Example:

from spacer.messages import DataLocation, ClassifyFeaturesMsg
from spacer.tasks import classify_features

message = ClassifyFeaturesMsg(
    # For your bookkeeping.
    job_token='image1',
    # Where the input feature-vector should be read from.
    feature_loc=DataLocation('filesystem', '/path/to/image1.featurevector'),
    # Where the classifier should be read from.
    classifier_loc=DataLocation('filesystem', '/path/to/classifier1.pkl'),
)
return_message = classify_features(message)
print(f"Classification runtime: {return_message.runtime:.1f} s")
print(f"Classes (recognized labels): {return_message.classes}")
print(
    "Classifier's scores for each point in the feature vector;"
    " scores are posterior probabilities of each class, with classes"
    " ordered as above:")
for row, col, scores in return_message.scores:
    print(f"Row {row}, column {col}: {scores}")

The label which has the highest score for a particular point (row-column position) can be considered the classifier's predicted label for that point.

One possible usage strategy is to trust the classifier's predictions for points where the highest confidence score is above a certain threshold, such as 0.8 (80%), and have human annotators check all other points.

classify_image

This basically does extract_features and classify_features together in one go, without needing to specify a storage location for the feature vector.

Takes an image, a list of pixel locations on that image, a feature extractor, and a classifier. Produces prediction results (scores) for the image points, as posterior probabilities for each class. Example:

from spacer.extract_features import EfficientNetExtractor
from spacer.messages import DataLocation, ClassifyImageMsg
from spacer.tasks import classify_image

message = ClassifyImageMsg(
    # For your bookkeeping.
    job_token='image1',
    # Where the input image should be read from.
    image_loc=DataLocation('filesystem', '/path/to/image1.jpg'),
    # Instantiated feature extractor.
    extractor=EfficientNetExtractor(
        data_locations=dict(
            weights=DataLocation('filesystem', '/path/to/weights.pt'),
        ),
    ),
    # (row, column) tuples specifying pixel locations in the image.
    # Note that row is y, column is x.
    rowcols=[(2200, 1000), (1400, 1500), (3000, 450)],
    # Where the classifier should be read from.
    classifier_loc=DataLocation('filesystem', '/path/to/classifier1.pkl'),
)
return_message = classify_image(message)
print(f"Runtime: {return_message.runtime:.1f} s")
print(f"Classes (recognized labels): {return_message.classes}")
print(
    "Classifier's scores for each point in rowcols;"
    " scores are posterior probabilities of each class, with classes"
    " ordered as above:")
for row, col, scores in return_message.scores:
    print(f"Row {row}, column {col}: {scores}")

Unit tests

If you are using the docker build or local install, you can run the test suite by running python -m unittest from the spacer directory.

• Expect many tests to be skipped, since most test fixtures aren't set up for public access yet.

• Run just a single test module with a command like python -m unittest tests.test_tasks, or just python -m tests.test_tasks (the latter invokes the if __name__ == '__main__': part of the module).

• You can get logging output during test runs with the LOG_DESTINATION and LOG_LEVEL vars in config.py.

You can check code coverage like so:

coverage run --source=spacer --omit=spacer/tests/* -m unittest    
coverage report -m
coverage html