precisionRecall

Get precision recall metrics of instance segmentation results

Since R2024b

Syntax

[precision,recall,scores] = precisionRecall(metrics)

[precision,recall,scores] = precisionRecall(metrics,Name=Value)

Description

[precision,recall,scores] = precisionRecall(metrics) gets the precision, recall, and prediction score values for all classes in the ClassNames property and all overlap thresholds in the OverlapThreshold property of the instanceSegmentationMetrics object metrics.

[precision,recall,scores] = precisionRecall(metrics,Name=Value) specifies precision and recall evaluation options using one or more name-value arguments. For example, ClassNames=["cars" "people"] specifies to get the precision recall metrics for the cars and people classes.

Input Arguments

metrics — instance segmentation performance metrics

instanceSegmentationMetrics object

instance segmentation performance metrics, specified as an instanceSegmentationMetrics object.

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Example: [precision,recall,scores]=precisionRecall(metrics,ClassNames=[cars people]) specifies the precision recall metric to be evaluated for the cars and people classes.

ClassNames — Class names

string array | cell array of character vectors

Class names of detected objects, specified as an array of strings or a cell array of character vectors. By default, the precisionRecall function returns the precision recall metrics for all classes specified by the ClassNames property of the instanceSegmentationMetrics object.

OverlapThresholds — Overlap threshold

numeric scalar | numeric vector

Overlap threshold, or Intersection over Union (IoU) threshold, for which to get the precision recall metrics, specified as a numeric scalar or numeric vector of box overlap threshold values. By default, the precisionRecall object function returns the precision and recall metrics for all overlap thresholds specified by the OverlapThreshold property of the instanceSegmentationMetrics object. To learn more about how to use overlap thresholds to evaluate instance segmentation results, see Evaluate Network Performance Using Precision Recall at Multiple Overlap Thresholds.

Output Arguments

precision — Precision

M-by-N cell array

Precision, returned as an M-by-N cell array. M is the number of classes in the ClassNames property, and N is the number of overlap thresholds in the OverlapThreshold property of the instanceSegmentationMetrics object metrics. Each element of the cell array contains a (numPredictions+1)-element numeric vector of precision values, sorted in descending order of prediction confidence scores. numPredictions is the number of predicted object masks.

Precision is the ratio of the number of true positives (TP) and the total number of predicted positives​. Larger precision scores indicate that more predicted object masks match ground truth objects. To learn more about the precision metric, see Compute Precision and Recall.

recall — Recall

M-by-N cell array

Recall, returned as an M-by-N cell array. M is the number of classes in the ClassNames property, and N is the number of overlap thresholds in the OverlapThreshold property of the instanceSegmentationMetrics object metrics. Each element of the cell array contains a (numPredictions+1)-element numeric vector of recall values, sorted in order of prediction confidence scores. numPredictions is the number of predicted object masks.

Recall is the ratio of true positives (TP) to the sum of true positives and false negatives (FN), where false negatives represent instances in the image that the model incorrectly classified as background or missed entirely. Larger recall scores indicate that the instance segmentation model is effectively identifying most of the actual instances within the images. To learn more about the recall metric, see Compute Precision and Recall.

scores — Confidence score

M-by-1 cell array

Confidence score for each instance segmentation, returned as an M-by-1 cell array. M is the number of classes in the ClassNames property. Each element of the array is a (numPredictions+1)-element numeric vector. numPredictions is the number of predicted object masks.

More About

Evaluate Network Performance Using Precision Recall at Multiple Overlap Thresholds

To evaluate how precisely a network can localize object instances, plot the precision recall curve for a range of overlap thresholds.

At higher overlap thresholds, the criteria for how well the object masks and ground truth masks must overlap to be a true positive (TP) are stricter. Therefore, average precision is lower at higher overlap thresholds, which corresponds to a decrease in the area under the precision-recall curve, which plots the recall against precision. Plotting the precision-recall curves across different overlap thresholds can help you evaluate the instance segmentation network in these ways.

• Evaluate how well the network identifies object classes at higher overlap thresholds.

• Identify specific overlap thresholds where network performance is significantly lower, highlighting areas for model improvement.

• Choose an overlap threshold that balances the tradeoff between identifying as many object instances as possible (high recall) and ensuring high accuracy in those detections (high precision).

• Use precision-recall curves at different overlap thresholds for a more granular comparison between instance segmentation models than single metric evaluations. Nuances in performance can be obscured when considering only one overlap threshold or when relying solely on aggregated metrics such as mean average precision.

Algorithms

Compute Precision and Recall

Precision recall is a powerful tool you can use to evaluate instance segmentation network performance. The precisionRecall function computes the precision and recall in these steps.

1. Sorts object instances in descending order based on their confidence scores. Higher confidence scores indicate that the model is more certain that the instance segmentation is correct.

2. Identifies true positives (TP) and false positives (FP) according to the specified overlap threshold criteria. A segmentation is considered a TP if its IoU is greater to or equal to the specified overlap threshold. A segmentation is considered an FP if it does not match any ground truth object or if it matches a ground truth object but the IoU is below the specified overlap threshold.

3. Starting with the instance segmentation with the highest confidence score, the precisionRecall function iterates through each instance and calculates the cumulative number of TPs and FPs at each step. This step-by-step process enables the calculation of precision and recall at every confidence level. At each score, the function calculates the precision and recall.

   Precision measures the accuracy of positive predictions, consisting of the proportion of correctly detected instances from all object instances.

   Precision = TP / (TP + FP)

   Recall measures the ability of the network to detect all object instances, consisting of the proportion of actual instances that the network correctly identifies. False negatives (FNs) are ground truth objects the network misses or detects with a confidence score below the specified threshold.

   Recall = TP / (TP + FN)

4. For each instance segmentation, the set of TPs, FPs, and FNs changes, which enables you to recalculate precision and recall at each confidence level.

To visualize the tradeoff between precision and recall for different confidence thresholds, plot the calculated precision and recall values. For an example, see Perform Instance Segmentation Using SOLOv2.

Version History

Introduced in R2024b