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trainFasterRCNNObjectDetector

Train a Faster R-CNN deep learning object detector

Description

example

trainedDetector = trainFasterRCNNObjectDetector(trainingData,network,options) trains a Faster R-CNN (regions with convolution neural networks) object detector using deep learning. You can train a Faster R-CNN detector to detect multiple object classes.

This function requires that you have Deep Learning Toolbox™. It is recommended that you also have Parallel Computing Toolbox™ to use with a CUDA®-enabled NVIDIA® GPU with compute capability 3.0 or higher.

trainedDetector = trainFasterRCNNObjectDetector(trainingData,checkpoint,options) resumes training from a detector checkpoint.

trainedDetector = trainFasterRCNNObjectDetector(trainingData,detector,options) continues training a Faster R-CNN object detector. Use this syntax for fine-tuning a detector.

trainedDetector = trainFasterRCNNObjectDetector(___,Name,Value) uses additional options specified by one or more Name,Value pair arguments and any of the previous inputs.

[trainedDetector,info] = trainFasterRCNNObjectDetector(___) also returns information on the training progress, such as training loss and accuracy, for each iteration.

Examples

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trainingData = data.vehicleTrainingData;

trainingData.imageFilename = fullfile(toolboxdir('vision'),'visiondata', ...
trainingData.imageFilename);

Randomly shuffle data for training.

rng(0);
shuffledIdx = randperm(height(trainingData));
trainingData = trainingData(shuffledIdx,:);

Create an image datastore using the files from the table.

imds = imageDatastore(trainingData.imageFilename);

Create a box label datastore using the label columns from the table.

blds = boxLabelDatastore(trainingData(:,2:end));

Combine the datastores.

ds = combine(imds, blds);

Set up the network layers.

lgraph = layerGraph(data.detector.Network)
lgraph =
LayerGraph with properties:

Layers: [21×1 nnet.cnn.layer.Layer]
Connections: [22×2 table]

Configure training options.

options = trainingOptions('sgdm', ...
'MiniBatchSize', 1, ...
'InitialLearnRate', 1e-3, ...
'MaxEpochs', 7, ...
'VerboseFrequency', 200, ...
'CheckpointPath', tempdir);

Train detector. Training will take a few minutes. Adjust the NegativeOverlapRange and PositiveOverlapRange to ensure training samples tightly overlap with ground truth.

detector = trainFasterRCNNObjectDetector(trainingData, lgraph, options, ...
'NegativeOverlapRange',[0 0.3], ...
'PositiveOverlapRange',[0.6 1]);
*************************************************************************
Training a Faster R-CNN Object Detector for the following object classes:

* vehicle

Training on single GPU.
|=============================================================================================================================================|
|  Epoch  |  Iteration  |  Time Elapsed  |  Mini-batch  |  Mini-batch  |  Mini-batch  |  RPN Mini-batch  |  RPN Mini-batch  |  Base Learning  |
|         |             |   (hh:mm:ss)   |     Loss     |   Accuracy   |     RMSE     |     Accuracy     |       RMSE       |      Rate       |
|=============================================================================================================================================|
|       1 |           1 |       00:00:00 |       1.3189 |      100.00% |         0.61 |           68.75% |             1.08 |          0.0010 |
|       1 |         200 |       00:00:57 |       0.5058 |       97.50% |         0.21 |           90.62% |             0.64 |          0.0010 |
|       2 |         400 |       00:02:01 |       1.0283 |       94.03% |         0.12 |           91.41% |             1.02 |          0.0010 |
|       3 |         600 |       00:03:03 |       0.9443 |      100.00% |              |           81.25% |             1.20 |          0.0010 |
|       3 |         800 |       00:04:01 |       1.3437 |      100.00% |              |           62.50% |             1.32 |          0.0010 |
|       4 |        1000 |       00:05:03 |       1.4966 |      100.00% |              |           42.19% |             0.83 |          0.0010 |
|       5 |        1200 |       00:06:06 |       0.4891 |      100.00% |         0.15 |           93.75% |             0.68 |          0.0010 |
|       5 |        1400 |       00:07:04 |       0.8458 |      100.00% |              |           92.97% |             1.01 |          0.0010 |
|       6 |        1600 |       00:08:06 |       1.0399 |      100.00% |              |           73.44% |             1.08 |          0.0010 |
|       7 |        1800 |       00:09:09 |       0.5232 |       95.24% |         0.22 |           91.41% |             0.68 |          0.0010 |
|       7 |        2000 |       00:10:07 |       0.6197 |      100.00% |         0.20 |           79.69% |             0.66 |          0.0010 |
|       7 |        2065 |       00:10:25 |       0.4209 |      100.00% |         0.24 |           88.28% |             0.61 |          0.0010 |
|=============================================================================================================================================|
Detector training complete.
*******************************************************************

Test the Faster R-CNN detector on a test image.

Run the detector.

[bbox, score, label] = detect(detector,img);

Display detection results.

detectedImg = insertShape(img,'Rectangle',bbox);
figure
imshow(detectedImg)

Input Arguments

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Labeled ground truth, specified as a datastore or a table.

Each bounding box must be in the format [x y width height].

• If you use a datastore, calling the datastore with the read and readall functions must return a cell array or table with three columns, {images,boxes,labels}.

• images — The first column must be a cell vector of images that can be grayscale, RGB, or a M-by-N-by-P multichannel image.).

• boxes — The second column must be a cell vector that contains M-by-4 matrices of bounding boxes in the format [x,y,width,height]. The vectors represent the location and size of bounding boxes for the objects in each image.

• labels — The third column must be a cell vector that contains M-by-1 categorical vectors containing object class names. All categorical data returned by the datastore must contain the same categories.

You can use the combine function to create the datastore to use for training.

• imageDatastore — Create a datastore containing images.

• boxLabelDatastore — Create a datastore containing bounding boxes and labels.

• combine(imds,blds) — Combine images, bounding boxes, and labels into one datastore.

• If you use a table, the table must have two or more columns. The first column of the table must contain image file names with paths. The images must be grayscale or truecolor (RGB) and they can be in any format supported by imread. Each of the remaining columns must be a cell vector that contains M-by-4 matrices that represent a single object class, such as vehicle, flower, or stop sign. The columns contain 4-element double arrays of M bounding boxes in the format [x,y,width,height]. The format specifies the upper-left corner location and size of the bounding box in the corresponding image. To create a ground truth table, you can use the Image Labeler app or Video Labeler app. To create a table of training data from the generated ground truth, use the objectDetectorTrainingData function.

Network, specified as a SeriesNetwork, an array of Layer objects, a layerGraph object, or by the network name. The network is trained to classify the object classes defined in the trainingData table. To use SeriesNetwork, Layer, and layerGraph objects, you must have Deep Learning Toolbox.

• When you specify the network as a SeriesNetwork, an array of Layer objects, or by the network name, the function transforms the network into a Faster R-CNN network by adding a region proposal network (RPN), an ROI max pooling layer, and new classification and regression layers to support object detection. Additionally, the GridSize property of the ROI max pooling layer is set to the output size of the last max pooling layer in the network.

• The array of Layer objects must contain a classification layer that supports the number of object classes, plus a background class. Use this input type to customize the learning rates of each layer. An example of an array of Layer objects follows:

layers = [imageInputLayer([28 28 3])
convolution2dLayer([5 5],10)
reluLayer()
fullyConnectedLayer(10)
softmaxLayer()
classificationLayer()];

• When you specify the network as SeriesNetwork object, Layer array, or by the network name, the weights for additional convolution and fully connected layers are initialized to 'narrow-normal'. The function adds these weights to create the network.

• The network name must be one of the following valid network names. You must also install the corresponding add-on.

Network NameFeature Extraction Layer NameROI Pooling Layer OutputSizeDescription
alexnet'relu5'[6 6]Last max pooling layer is replaced by ROI max pooling layer
vgg16'relu5_3'[7 7]
vgg19'relu5_4'
squeezenet'fire5-concat'[14 14]
resnet18'res4b_relu'ROI pooling layer is inserted after the feature extraction layer.
resnet50'activation_40_relu'
resnet101'res4b22_relu'
mobilenetv2'block_13_expand_relu'
inceptionv3'mixed7'[17 17]
inceptionresnetv2'block17_20_ac'

• The LayerGraph object must be a valid Faster R-CNN object detection network. You can use the fasterRCNNLayers function to create a LayerGraph object to train a custom Faster R-CNN network.

Tip

If your network is a DAGNetwork, use the layerGraph function to convert the network to a LayerGraph object. Then, create a custom Faster R-CNN network as described by the Create Faster R-CNN Object Detection Network example.

For more information on creating a Faster R-CNN network, see Getting Started with R-CNN, Fast R-CNN, and Faster R-CNN.

Training options, returned by the trainingOptions function (requires Deep Learning Toolbox). To specify solver and other options for network training, use trainingOptions.

Note

trainFasterRCNNObjectDetector does not support these training options:

• 'training-progress' value for 'Plots' argument

• 'ValidationData', 'ValidationFrequency', and 'ValidationPatience' argument

• 'OutputFcn' argument.

Additionally, the function does not support the following training options if you use a combined datastore input:

• 'once' and 'every-epoch' values for 'Shuffle' argument

• 'parallel' and 'multi-gpu' values for 'ExecutionEnvironment' argument

Saved detector checkpoint, specified as a fasterRCNNObjectDetector object. To save the detector after every epoch, set the 'CheckpointPath' property when using the trainingOptions function. Saving a checkpoint after every epoch is recommended because network training can take a few hours.

To load a checkpoint for a previously trained detector, load the MAT-file from the checkpoint path. For example, if the 'CheckpointPath' property of options is '/tmp', load a checkpoint MAT-file using:

The name of the MAT-file includes the iteration number and a timestamp indicating when the detector checkpoint was saved. The detector is saved in the detector variable of the file. Pass this file back into the trainFasterRCNNObjectDetector function:

frcnn = trainFasterRCNNObjectDetector(stopSigns,...
data.detector,options);

Previously trained Faster R-CNN object detector, specified as a fasterRCNNObjectDetector object. Use this syntax to continue training a detector with additional training data or to perform more training iterations to improve detector accuracy.

Name-Value Pair Arguments

Specify optional comma-separated pairs of Name,Value arguments. Name is the argument name and Value is the corresponding value. Name must appear inside quotes. You can specify several name and value pair arguments in any order as Name1,Value1,...,NameN,ValueN.

Example: 'PositiveOverlapRange',[0.75 1]

Training method, specified as the comma-separated pair consisting of 'TrainingMethod' and either 'end-to-end' or 'four-step'.

• 'end-to-end' — Simultaneously train the region proposal and region classification subnetworks.

• 'four-step' — Separately train the region proposal and region classification subnetworks in four steps.

Bounding box overlap ratios for positive training samples, specified as the comma-separated pair consisting of 'PositiveOverlapRange' and one of the following:

• A 2-element vector that specifies an identical overlap ratio for all four training stages.

• A 2-by-2 matrix, used only for the end-to-end training method. The first row of the matrix defines the overlap ratios for the region proposal subnetwork. The second row defines the overlap ratios for the region classification subnetwork.

• A 4-by-2 matrix, used only for the four-step training method. Each row of the matrix specifies the overlap ratio for each of the four training stages.

Values are in the range [0,1]. Region proposals that overlap with ground truth bounding boxes within the specified range are used as positive training samples.

The overlap ratio used for both the PositiveOverlapRange and NegativeOverlapRange is defined as:

$\frac{area\left(A\cap B\right)}{area\left(A\cup B\right)}$

A and B are bounding boxes.

Bounding box overlap ratios for negative training samples, specified as the comma-separated pair consisting of 'NegativeOverlapRange' and one of the following.

• A 2-element vector that specifies the overlap ratio.

• A 2-by-2 matrix, used only for the end-to-end training method. The first row of the matrix defines the overlap ratios for the region proposal subnetwork. The second row defines the overlap ratios for the region classification subnetwork.

• A 4-by-2 matrix, used only for the four-step training method. Each row of the matrix specifies the overlap ratio for each of the four training stages.

Values are in the range [0,1]. Region proposals that overlap with the ground truth bounding boxes within the specified range are used as negative training samples.

The overlap ratio used for both the PositiveOverlapRange and NegativeOverlapRange is defined as:

$\frac{area\left(A\cap B\right)}{area\left(A\cup B\right)}$

A and B are bounding boxes.

Maximum number of strongest region proposals to use for generating training samples, specified as the comma-separated pair consisting of 'NumStrongestRegions' and a positive integer. Reduce this value to speed up processing time at the cost of training accuracy. To use all region proposals, set this value to Inf.

Number of region proposals to randomly sample from each training image, specified as an integer, 1-by-2 vector, or a 1-by-4 vector. Use the 1-by-2 vector for end-to-end training. Use the 1-by-4 vector for the four-step training. Reduce the number of regions to sample to reduce memory usage and speed up training. Reducing the value can also decrease training accuracy.

When you set 'TrainingMethod' to 'end-to-end', the number of region proposals can be set to a 1-by-2 vector. The first element of the vector must be the number of regions sampled for the region proposal subnetwork. The second element must be the number of regions sampled for the region classfication subnetwork.

When you set 'TrainingMethod' to 'four-step', the number of region proposals can be set to a 1-by-4 vector. The ith element specifies the number of regions to sample for the ith training step.

Length of the smallest image dimension, either width or height, specified as the comma-separated pair consisting of 'SmallestImageDimension' and a positive integer. Training images are resized such that the length of the shortest dimension is equal to the specified integer. By default, training images are not resized. Resizing training images helps reduce computational costs and memory used when training images are large. Typical values range from 400–600 pixels.

Dependencies

• The SmallestImageDimension property supports only table input training data. To resize the input data of a datastore input, use the transform function.

Minimum anchor box sizes for building the anchor box pyramid of the region proposal network (RPN), specified as the comma-separated pair consisting of'MinBoxSizes' and an m-by-2 matrix. Each row defines the [height width] of an anchor box.

The default 'auto' setting uses the minimum size and the median aspect ratio from the bounding boxes for each class in the ground truth data. To remove redundant box sizes, the function keeps boxes that have an intersection-over-union value that is less than or equal to 0.5. This behavior ensures that the minimum number of anchor boxes is used to cover all the object sizes and aspect ratios.

When anchor boxes are computed based on MinBoxSizes, the ith anchor box size is:

round(MinBoxSizes(i,:) .* BoxPyramidScale ,^ (0:NumBoxPyramidLevels-1)')

Dependencies

• You cannot use this property if you specify the network as a LayerGraph object or if you resume training from a detector checkpoint.

• The MinBoxSizes property supports only input training in table format. To estimate anchor boxes for a datastore input, use the estimateAnchorBoxes function.

Anchor box pyramid scale factor used to successively upscale anchor box sizes, specified as the comma-separated pair consisting of 'BoxPyramidScale' and a scalar. Recommended values are from 1 through 2. Increase this value for faster results. Decrease the number for greater accuracy.

Dependencies

• The BoxPyramidScale property supports only input training data in table format. To estimate anchor boxes for a datastore input, use the estimateAnchorBoxes function.

Number of levels in an anchor box pyramid, specified as the comma-separated pair consisting of 'NumBoxPyramidLevels' and a scalar. Select a value that ensures that the multiscale anchor boxes are comparable in size to the size of objects in the ground truth data.

The default setting 'auto' selects the number of levels based on the size of objects within the ground truth data. The number of levels is selected such that it covers the range of object sizes.

Dependencies

• The NumBoxPyramidLevels property supports only input training data in table format. To estimate anchor boxes for a datastore input, use the estimateAnchorBoxes function.

Frozen batch normalization during training, specified as the comma-separated pair consisting of 'FreezeBatchNormalization' and true or false. The value indicates whether to freeze the input layers to the network during training. Set this value to true if you are training with a small mini-batch size. Small batch sizes result in poor estimates of the batch mean and variance, which are required for effective batch normalization.

If you do not specify a value for 'FreezeBatchNormalization', the function sets the property to:

• true if the 'MiniBatchSize' name-value argument for the trainingOptions function is less than 8.

• false if the 'MiniBatchSize' name-value argument for the trainingOptions function is greater than or equal to 8.

You must specify a value for 'FreezeBatchNormalization' to overide this default behavior.

Output Arguments

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Trained Faster R-CNN object detector, returned as a fasterRCNNObjectDetector object.

Training information, returned as a structure array with four elements. Each element corresponds to stage in the training of the Faster R-CNN network, and has the following fields. Each field is a numeric vector with one element per training iteration. Values that have not been calculated at a specific iteration are represented by NaN.

• TrainingLoss — Training loss at each iteration. This is the combination of the classification and regression loss used to train the Faster R-CNN network.

• TrainingAccuracy — Training set accuracy at each iteration

• TrainingRMSE — Training root mean square error (RMSE) for the box regression layer

• BaseLearnRate — Learning rate at each iteration

Tips

• To accelerate data preprocessing for training, trainFastRCNNObjectDetector automatically creates and uses a parallel pool based on your parallel preference settings. For more details about setting these preferences, see parallel preference settings. Using parallel computing preferences requires Parallel Computing Toolbox.

• VGG-16, VGG-19, ResNet-101, and Inception-ResNet-v2 are large models. Training with large images can produce "out-of-memory" errors. To mitigate these errors, try one or more of these options:

• This function supports transfer learning. When you input a network by name, such as 'resnet50', then the function automatically transforms the network into a valid Faster R-CNN network model based on the pretrained resnet50 model. Alternatively, manually specify a custom Faster R-CNN network by using the LayerGraph extracted from a pretrained DAG network. For more details, see Create Faster R-CNN Object Detection Network.

• This table describes how to transform each named network into a Faster R-CNN network. The feature extraction layer name specifies the layer for processing by the ROI pooling layer. The ROI output size specifies the size of the feature maps output by the ROI pooling layer.

Network NameFeature Extraction Layer NameROI Pooling Layer OutputSizeDescription
alexnet'relu5'[6 6]Last max pooling layer is replaced by ROI max pooling layer
vgg16'relu5_3'[7 7]
vgg19'relu5_4'
squeezenet'fire5-concat'[14 14]
resnet18'res4b_relu'ROI pooling layer is inserted after the feature extraction layer.
resnet50'activation_40_relu'
resnet101'res4b22_relu'
mobilenetv2'block_13_expand_relu'
inceptionv3'mixed7'[17 17]
inceptionresnetv2'block17_20_ac'

For information on modifying how a network is transformed into a Faster R-CNN network, see Design an R-CNN, Fast R-CNN, and a Faster R-CNN Model.

• During training, multiple image regions are processed from the training images The number of image regions per image is controlled by the NumRegionsToSample property. The PositiveOverlapRange and NegativeOverlapRange properties control which image regions are used for training. Positive training samples are those that overlap with the ground truth boxes by 0.6 to 1.0, as measured by the bounding box intersection-over-union metric (IoU). Negative training samples are those that overlap by 0 to 0.3. Choose values for these properties by testing the trained detector on a validation set.

Overlap ValuesDescription
PositiveOverlapRange set to [0.6 1]Positive training samples are set equal to the samples that overlap with the ground truth boxes by 0.6 to 1.0, measured by the bounding box IoU metric.
NegativeOverlapRange set to [0 0.3]Negative training samples are set equal to the samples that overlap with the ground truth boxes by 0 to 0.3.

If you set PositiveOverlapRange to [0.6 1], then the function sets the positive training samples equal to the samples that overlap with the ground truth boxes by 0.6 to 1.0, measured by the bounding box IoU metric. If you set NegativeOverlapRange to [0 0.3], then the function sets the negative training samples equal to the samples that overlap with the ground truth boxes by 0 to 0.3.

• Use the trainingOptions function to enable or disable verbose printing.

Compatibility Considerations

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Behavior changed in R2019b

References

[1] Ren, S., K. He, R. Girschick, and J. Sun. "Faster R-CNN: Towards Real-Time Object Detection with Region Proposal Networks." Advances in Neural Information Processing Systems. Vol. 28, 2015.

[2] Girshick, R. "Fast R-CNN." Proceedings of the IEEE International Conference on Computer Vision, 1440-1448. Santiago, Chile: IEEE, 2015.

[3] Girshick, R., J. Donahue, T. Darrell, and J. Malik. "Rich Feature Hierarchies for Accurate Object Detection and Semantic Segmentation." Proceedings of the 2014 IEEE Conference on Computer Vision and Pattern Recognition, 580-587. Columbus, OH: IEEE, 2014.

[4] Zitnick, C. L., and P. Dollar. "Edge Boxes: Locating Object Proposals from Edges." Computer Vision-ECCV 2014, 391-405. Zurich, Switzerland: ECCV, 2014.