Creating Operator classes¶
Operator Class¶
Each Operator class inherits Operator class.
1from pathlib import Path
2from monai.deploy.core import (ExecutionContext, Image, InputContext,
3 Operator, OutputContext, OperatorSpec)
4
5
6class MyOperator(Operator):
7 """Sample Operator implementation."""
8
9 def setup(self, spec: OperatorSpec):
10 spec.input("image_path")
11 spec.output("image")
12 spec.output("metadata")
13
14 def compute(self, op_input: InputContext, op_output: OutputContext, context: ExecutionContext):
15 from skimage import filters, io
16
17 # Get input image
18 image_path = Path(op_input.receive("image_path")) # omitting validation for brevity
19 if image_path.is_dir():
20 image_path = next(image_path.glob("*.*")) # take the first file
21 input_image = io.imread(image_path)
22
23 # Get mask image
24 mask = op_input.get("mask").asnumpy()
25
26 # Apply filter
27 output_image = filters.sobel(input_image, mask)
28
29 # Prepare output metadata
30 metadata = {"shape": input_image.shape, "dtype": input_image.dtype}
31
32 # Set output
33 op_output.emit(Image(output_image), "image")
34 op_output.emit(metadata, "metadata")
setup() method¶
In prior releases, the input and output properties of the operator are specified by using @input and @output decorators, but starting with release v0.6, the setup() method is used.
compute() method¶
compute() method in Operator class is an abstract method that needs to be implemented by the Operator developer.
Please check the description of compute() method to find a way to access
Operator’s input/output
Application’s input/output
Model’s name/path/predictor
Note that, if the operator is a leaf operator in the workflow graph and the operator output is file(s) written to the file system, the path needs to be set using the operator’s constructor or a named input for path object or string. The leaf operator can also have in-memory output(s) without requiring other operator(s) as receiver, if the output is configured correctly like in the GaussionOperator in Simple Image Processing App
Package dependencies¶
The dependencies of the operator need to be captured in a “requirements.txt”, instead of using the @env decorator as in earlier releases. The aggregated requirement definitions for an application are then store in a consolidated “requirements.txt” file, to be installed at packaging time.
Creating a Reusable Operator¶
You can create a common Operator class so that other Operator classes can just inherit the common Operator and implement only part of the compute() method to handle specific cases.
Please refer to the following examples: