Pipeline Classifier

This example creates a model which can be used to train a simple drawing / sketch classifier based on user examples. The model is a pipeline composed of a drawing embedding model and a nearest neighbor classifier.

The model is updatable and starts off "empty", meaning the nearest neighbor classifier has no examples or labels. Before updating with training examples the model predicts "unknown" for all input.
The input to the model is a 28 x 28 grayscale drawing. The background is expected to be black (0) while the strokes of the drawing should be rendered as white (255). For example:

Drawing of a Star


Drawing of a Heart


Drawing of 5


Get the Embedding Model

The drawing embedding model will be used as a feature extractor. Start by getting the first part of the model, the spec:

import coremltools
from coremltools.models import MLModel

embedding_path = './models/TinyDrawingEmbedding.mlmodel'
embedding_model = MLModel(embedding_path)

embedding_spec = embedding_model.get_spec()
print embedding_spec.description
tf.estimator package not installed.
tf.estimator package not installed.
input {
  name: "drawing"
  shortDescription: "Input sketch image with black background and white strokes"
  type {
    imageType {
      width: 28
      height: 28
      colorSpace: GRAYSCALE
output {
  name: "embedding"
  shortDescription: "Vector embedding of sketch in 128 dimensional space"
  type {
    multiArrayType {
      shape: 128
      dataType: FLOAT32
metadata {
  shortDescription: "Embeds a 28 x 28 grayscale image of a sketch into 128 dimensional space. The model was created by removing the last layer of a simple convolution based neural network classifier trained on the Quick, Draw! dataset (https://github.com/googlecreativelab/quickdraw-dataset)."
  author: "Core ML Tools Example"
  license: "MIT"

In the Out tab, the shortDescription indicates that the embedding model takes in a 28x28 grayscale image about outputs a 128 dimensional float vector.

Create the Nearest Neighbor Classifier

Now that the feature extractor is in place, create the second model of our pipeline model. It is a nearest neighbor classifier operating on the embedding.

from coremltools.models.nearest_neighbors import KNearestNeighborsClassifierBuilder
import coremltools.models.datatypes as datatypes

knn_builder = KNearestNeighborsClassifierBuilder(input_name='embedding',

knn_builder.author = 'Core ML Tools Example'
knn_builder.license = 'MIT'
knn_builder.description = 'Classifies 128 dimension vector based on 3 nearest neighbors'

knn_spec = knn_builder.spec
knn_spec.description.input[0].shortDescription = 'Input vector to classify'
knn_spec.description.output[0].shortDescription = 'Predicted label. Defaults to \'unknown\''
knn_spec.description.output[1].shortDescription = 'Probabilities / score for each possible label.'

# print knn_spec.description

Create an Updatable Pipeline Model

The last step is to create the pipeline model and insert the feature extractor and the nearest neighbor classifier. The model will be set to be updatable.

  1. Create the spec and set it to be updatable and the specification version:
pipeline_spec = coremltools.proto.Model_pb2.Model()
pipeline_spec.specificationVersion = coremltools._MINIMUM_UPDATABLE_SPEC_VERSION
pipeline_spec.isUpdatable = True
  1. Set the inputs to the inputs from the embedding model:
# Inputs are the inputs from the embedding model
  1. Set the outputs to the outputs from the classification model:
# Outputs are the outputs from the classification model
pipeline_spec.description.predictedFeatureName = knn_spec.description.predictedFeatureName
pipeline_spec.description.predictedProbabilitiesName = knn_spec.description.predictedProbabilitiesName
  1. Set the training inputs:
# Training inputs
pipeline_spec.description.trainingInput[0].shortDescription = 'Example sketch'
pipeline_spec.description.trainingInput[1].shortDescription = 'Associated true label of example sketch'
  1. Provide the metadata:
# Provide metadata
pipeline_spec.description.metadata.author = 'Core ML Tools'
pipeline_spec.description.metadata.license = 'MIT'
pipeline_spec.description.metadata.shortDescription = ('An updatable model which can be used to train a tiny 28 x 28 drawing classifier based on user examples.'
                                                       ' It uses a drawing embedding trained on the Quick, Draw! dataset (https://github.com/googlecreativelab/quickdraw-dataset)')
  1. Construct the pipeline by adding the embedding and the nearest neighbor classifier:
# Construct pipeline by adding the embedding and then the nearest neighbor classifier
  1. Save the updated spec:
# Save the updated spec.
from coremltools.models import MLModel
mlmodel = MLModel(pipeline_spec)

output_path = './TinyDrawingClassifier.mlmodel'
from coremltools.models.utils import save_spec