The basic idea behind Custom Vision is to take a pre-built image recognition model supplied by Azure, and customise it for your needs by supplying a set of images with which to update it. All model training and prediction is done in the cloud, so you don’t need a powerful machine. Similarly, since you are starting with a model that has already been trained, you don’t need a very large dataset or long training times to obtain good predictions (ideally). This vignette walks you through the process of creating and deploying a Custom Vision predictive service.
You can create the Custom Vision resources using the AzureRMR framework for interacting with Resource Manager. Note that Custom Vision requires at least two resources to be created: one for training, and one for prediction. The available service tiers for Custom Vision are
F0 (free, limited to 2 projects for training and 10k transactions/month for prediction) and
library(AzureVision) rg <- AzureRMR::get_azure_login("yourtenant")$ get_subscription("sub_id")$ get_resource_group("rgname") res <- rg$create_cognitive_service("mycustvis", service_type="CustomVision.Training", service_tier="S0") pred_res <- rg$create_cognitive_service("mycustvispred", service_type="CustomVision.Prediction", service_tier="S0")
Custom Vision defines two different types of endpoint: a training endpoint, and a prediction endpoint. Somewhat confusingly, they can both share the same hostname, but use different paths and authentication keys. To start, call the
customvision_training_endpoint function with the service URL and key.
Custom Vision is organised hierarchically. At the top level, we have a project, which represents the data and model for a specific task. Within a project, we have one or more iterations of the model, built on different sets of training images. Each iteration in a project is independent: you can create (train) an iteration, deploy it, and delete it without affecting other iterations.
You can see the projects that currently exist on the endpoint by calling
list_projects. This returns a named list of project objects:
$general_compact Azure Custom Vision project 'general_compact' (304fc776-d860-490a-b4ec-5964bb134743) Endpoint: https://australiaeast.api.cognitive.microsoft.com/customvision/v3.0 Domain: classification.general.compact (0732100f-1a38-4e49-a514-c9b44c697ab5) Export target: standard Classification type: Multiclass $general_multilabel Azure Custom Vision project 'general_multilabel' (c485f10b-cb54-47a3-b585-624488335f58) Endpoint: https://australiaeast.api.cognitive.microsoft.com/customvision/v3.0 Domain: classification.general (ee85a74c-405e-4adc-bb47-ffa8ca0c9f31) Export target: none Classification type: Multilabel $logo_obj Azure Custom Vision project 'logo_obj' (af82557f-6ead-401c-afd6-bb9d5a3b042b) Endpoint: https://australiaeast.api.cognitive.microsoft.com/customvision/v3.0 Domain: object_detection.logo (1d8ffafe-ec40-4fb2-8f90-72b3b6cecea4) Export target: none Classification type: NA
There are three different types of projects, as implied by the list above:
The functions to create these projects are
create_classification_project (which is used to create both multiclass and multilabel projects) and
create_object_detection_project. Let’s create a classification project:
Azure Custom Vision project 'testproj' (db368447-e5da-4cd7-8799-0ccd8157323e) Endpoint: https://australiaeast.api.cognitive.microsoft.com/customvision/v3.0 Domain: classification.general.compact (0732100f-1a38-4e49-a514-c9b44c697ab5) Export target: standard Classification type: Multiclass
Here, we specify the export target to be
standard to support exporting the final model to one of various standalone formats, eg TensorFlow, CoreML or ONNX. The default is
none, in which case the model stays on the Custom Vision server. The advantage of
none is that the model can be more complex, resulting in potentially better accuracy. The type of project is multiclass classification, and the domain (the initial model used as the basis for training) is
general. Other possible domains for classification include
Since a Custom Vision model is trained in Azure and not locally, we need to upload some images. The data we’ll use comes from the Microsoft Computer Vision Best Practices project. This is a simple set of images containing 4 kinds of objects one might find in a fridge: cans, cartons, milk bottles, and water bottles.
The generic function to add images to a project is
add_images, which takes a vector of filenames, Internet URLs or raw vectors as the images to upload. The method for classification projects also has an argument
tags which can be used to assign labels to the images as they are uploaded.
add_images returns a vector of image IDs, which are how Custom Vision keeps track of the images it uses. It should be noted that Custom Vision does not keep a record of the source filename or URL; it works only with image IDs. A future release of AzureVision may automatically track the source metadata, allowing you to associate an ID with an actual image. For now, this must be done manually.
Let’s upload the fridge objects to the project. We’ll keep aside 5 images from each class of object to use as validation data.
cans <- dir("fridgeObjects/can", full.names=TRUE) cartons <- dir("fridgeObjects/carton", full.names=TRUE) milk <- dir("fridgeObjects/milk_bottle", full.names=TRUE) water <- dir("fridgeObjects/water_bottle", full.names=TRUE) # upload all but 5 images from cans and cartons, and tag them can_ids <- add_images(testproj, cans[-(1:5)], tags="can") carton_ids <- add_images(testproj, cartons[-(1:5)], tags="carton")
If you don’t tag the images at upload time, you can do so later with
Other image functions to be aware of include
add_image_regions (which is for object detection projects). A useful one is
browse_images, which takes a vector of IDs and displays the corresponding images in your browser.
Having uploaded the data, we can train the Custom Vision model with
train_model. This trains the model on the server and returns a model iteration, which is the result of running the training algorithm on the current set of images. Each time you call
train_model, for example to update the model after adding or removing images, you will obtain a different model iteration. In general, you can rely on AzureVision to keep track of the iterations for you, and automatically return the relevant results for the latest iteration.
Azure Custom Vision model Project/iteration: testproj/Iteration 1 (f243bb4c-e4f8-473e-9df0-190a407472be)
Optional arguments to
training_method: Set this to “advanced” to force Custom Vision to do the training from scratch, rather than simply updating a pre-trained model. This also enables the other arguments below.
training_method == "advanced", the maximum runtime in hours for training the model. The default is 1 hour.
training_method == "advanced", whether to train the model anyway even if the images have not changed.
training_method == "advanced", an optional email address to send a notification to when the training is complete.
wait: Whether to wait until training completes before returning.
Other model iteration management functions are
get_model (to retrieve a previously trained iteration),
list_models (retrieve all previously trained iterations), and
We can examine the model performance on the training data (which may be different to the current data!) with the
summary method. For this toy problem, the model manages to obtain a perfect fit.
$perTagPerformance id name precision precisionStdDeviation recall 1 22ddd4bc-2031-43a1-b0ef-eb6b219eb6f7 can 1 0 1 2 301db6f9-b701-4dc6-8650-a9cf3fe4bb2e carton 1 0 1 3 594ad770-83e5-4c77-825d-9249dae4a2c6 milk_bottle 1 0 1 4 eda5869a-cc75-41df-9c4c-717c10f79739 water_bottle 1 0 1 recallStdDeviation averagePrecision 1 0 1 2 0 1 3 0 1 4 0 1 $precision  1 $precisionStdDeviation  0 $recall  1 $recallStdDeviation  0 $averagePrecision  1
Obtaining predictions from the trained model is done with the
predict method. By default, this returns the predicted tag (class label) for the image, but you can also get the predicted class probabilities by specifying
validation_tags predicted_tags can carton milk_bottle water_bottle can 4 0 0 0 carton 0 5 0 0 milk_bottle 1 0 5 0 water_bottle 0 0 0 5
can carton milk_bottle water_bottle [1,] 9.999968e-01 8.977501e-08 5.855104e-11 3.154334e-06 [2,] 9.732912e-01 3.454168e-10 4.610847e-06 2.670425e-02 [3,] 3.019476e-01 5.779990e-04 6.974699e-01 4.506565e-06 [4,] 5.072662e-01 2.849253e-03 4.856858e-01 4.198686e-03 [5,] 9.962270e-01 5.411842e-07 3.540882e-03 2.316211e-04 [6,] 3.145034e-11 1.000000e+00 2.574793e-10 4.242047e-14
This shows that the model got 19 out of 20 predictions correct on the validation data, misclassifying one of the cans as a milk bottle.
The code above demonstrates using the training endpoint to obtain predictions, which is really meant only for model testing and validation. For production purposes, we would normally publish a trained model to a Custom Vision prediction resource. Among other things, a user with access to the training endpoint has complete freedom to modify the model and the data, whereas access to the prediction endpoint only allows getting predictions.
Publishing a model requires knowing the Azure resource ID of the prediction resource. Here, we’ll use the resource object that was created earlier using AzureRMR; you can also obtain this information from the Azure Portal.
Once a model has been published, we can obtain predictions from the prediction endpoint in a manner very similar to previously. We create a predictive service object with
classification_service, and then call the
predict method. Note that a required input is the project ID; you can supply this directly or via the project object.
pred_url <- pred_res$properties$endpoint pred_key <- pred_res$list_keys() pred_endp <- customvision_prediction_endpoint(url=pred_url, key=pred_key) project_id <- testproj$project$id pred_svc <- classification_service(pred_endp, project_id, "iteration1") # predictions from prediction endpoint -- same as before predsvc_tags <- predict(pred_svc, validation_imgs) table(predsvc_tags, validation_tags)
validation_tags predsvc_tags can carton milk_bottle water_bottle can 4 0 0 0 carton 0 5 0 0 milk_bottle 1 0 5 0 water_bottle 0 0 0 5
As an alternative to deploying the model to an online predictive service resource, you can also export the model to a standalone format. This is only possible if the project was created to support exporting. The formats supported include:
To export the model, call
export_model and specify the target format. By default, the model will be downloaded to your local machine, but
export_model also (invisibly) returns a URL from where it can be downloaded independently.
Downloading to f243bb4c-e4f8-473e-9df0-190a407472be.TensorFlow.zip trying URL 'https://irisprodae...' Content type 'application/octet-stream' length 4673656 bytes (4.5 MB) downloaded 4.5 MB