yolo.m

%YOLO v3 Object Detection

doTraining = false;

if ~doTraining
    preTrainedDetector = downloadPretrainedYOLOv3Detector();    
end

%Load Data
unzip vehicleDatasetImages.zip
data = load('vehicleDatasetGroundTruth.mat');
vehicleDataset = data.vehicleDataset;

vehicleDataset.imageFilename = fullfile(pwd, vehicleDataset.imageFilename);

rng(0);
shuffledIndices = randperm(height(vehicleDataset));
idx = floor(0.6 * length(shuffledIndices));
trainingDataTbl = vehicleDataset(shuffledIndices(1:idx), :);
testDataTbl = vehicleDataset(shuffledIndices(idx+1:end), :);

imdsTrain = imageDatastore(trainingDataTbl.imageFilename);
imdsTest = imageDatastore(testDataTbl.imageFilename);

bldsTrain = boxLabelDatastore(trainingDataTbl(:, 2:end));
bldsTest = boxLabelDatastore(testDataTbl(:, 2:end));

trainingData = combine(imdsTrain, bldsTrain);
testData = combine(imdsTest, bldsTest);

validateInputData(trainingData);
validateInputData(testData);

% Data Augmentation
augmentedTrainingData = transform(trainingData, @augmentData);
% Visualize the augmented images.
augmentedData = cell(4,1);
for k = 1:4
    data = read(augmentedTrainingData);
    augmentedData{k} = insertShape(data{1,1}, 'Rectangle', data{1,2});
    reset(augmentedTrainingData);
end
%figure
montage(augmentedData, 'BorderSize', 10)

%Define YOLO v3 Object Detector
networkInputSize = [227 227 3];
rng(0)
trainingDataForEstimation = transform(trainingData, @(data)preprocessData(data, networkInputSize));
numAnchors = 6;
[anchors, meanIoU] = estimateAnchorBoxes(trainingDataForEstimation, numAnchors)

area = anchors(:, 1).*anchors(:, 2);
[~, idx] = sort(area, 'descend');
anchors = anchors(idx, :);
anchorBoxes = {anchors(1:3,:)
    anchors(4:6,:)
    };

baseNetwork = squeezenet;
classNames = trainingDataTbl.Properties.VariableNames(2:end);

yolov3Detector = yolov3ObjectDetector(baseNetwork, classNames, anchorBoxes, 'DetectionNetworkSource', {'fire9-concat', 'fire5-concat'});

preprocessedTrainingData = transform(augmentedTrainingData, @(data)preprocess(yolov3Detector, data));

data = read(preprocessedTrainingData);

I = data{1,1};
bbox = data{1,2};
annotatedImage = insertShape(I, 'Rectangle', bbox);
annotatedImage = imresize(annotatedImage,2);
%figure
imshow(annotatedImage)

reset(preprocessedTrainingData);

numEpochs = 80;
miniBatchSize = 8;
learningRate = 0.001;
warmupPeriod = 1000;
l2Regularization = 0.0005;
penaltyThreshold = 0.5;
velocity = [];

if canUseParallelPool
   dispatchInBackground = true;
else
   dispatchInBackground = false;
end

mbqTrain = minibatchqueue(preprocessedTrainingData, 2,...
        "MiniBatchSize", miniBatchSize,...
        "MiniBatchFcn", @(images, boxes, labels) createBatchData(images, boxes, labels, classNames), ...
        "MiniBatchFormat", ["SSCB", ""],...
        "DispatchInBackground", dispatchInBackground,...
        "OutputCast", ["", "double"]);

if doTraining
    
    % Create subplots for the learning rate and mini-batch loss.
    fig = figure;
    [lossPlotter, learningRatePlotter] = configureTrainingProgressPlotter(fig);

    iteration = 0;
    % Custom training loop.
    for epoch = 1:numEpochs
          
        reset(mbqTrain);
        shuffle(mbqTrain);
        
        while(hasdata(mbqTrain))
            iteration = iteration + 1;
           
            [XTrain, YTrain] = next(mbqTrain);
            
            % Evaluate the model gradients and loss using dlfeval and the
            % modelGradients function.
            [gradients, state, lossInfo] = dlfeval(@modelGradients, yolov3Detector, XTrain, YTrain, penaltyThreshold);
    
            % Apply L2 regularization.
            gradients = dlupdate(@(g,w) g + l2Regularization*w, gradients, yolov3Detector.Learnables);
    
            % Determine the current learning rate value.
            currentLR = piecewiseLearningRateWithWarmup(iteration, epoch, learningRate, warmupPeriod, numEpochs);
    
            % Update the detector learnable parameters using the SGDM optimizer.
            [yolov3Detector.Learnables, velocity] = sgdmupdate(yolov3Detector.Learnables, gradients, velocity, currentLR);
    
            % Update the state parameters of dlnetwork.
            yolov3Detector.State = state;
              
            % Display progress.
            displayLossInfo(epoch, iteration, currentLR, lossInfo);  
                
            % Update training plot with new points.
            updatePlots(lossPlotter, learningRatePlotter, iteration, currentLR, lossInfo.totalLoss);
        end        
    end
else
    yolov3Detector = preTrainedDetector;
end

results = detect(yolov3Detector,testData,'MiniBatchSize',8);

% Evaluate the object detector (Average Precision metric)
[ap,recall,precision] = evaluateDetectionPrecision(results,testData);

% Plot precision-recall curve.
plot(recall,precision)
xlabel('Recall')
ylabel('Precision')
grid on
title(sprintf('Average Precision = %.2f', ap))

data = read(testData);
I = data{1};

[bboxes,scores,labels] = detect(yolov3Detector,I);

I = insertObjectAnnotation(I,'rectangle',bboxes,scores);

figure
imshow(I)

function [gradients, state, info] = modelGradients(detector, XTrain, YTrain, penaltyThreshold)
inputImageSize = size(XTrain,1:2);

% Gather the ground truths in the CPU for post processing
YTrain = gather(extractdata(YTrain));

% Extract the predictions from the detector.
[gatheredPredictions, YPredCell, state] = forward(detector, XTrain);

% Generate target for predictions from the ground truth data.
[boxTarget, objectnessTarget, classTarget, objectMaskTarget, boxErrorScale] = generateTargets(gatheredPredictions,...
    YTrain, inputImageSize, detector.AnchorBoxes, penaltyThreshold);

% Compute the loss.
boxLoss = bboxOffsetLoss(YPredCell(:,[2 3 7 8]),boxTarget,objectMaskTarget,boxErrorScale);
objLoss = objectnessLoss(YPredCell(:,1),objectnessTarget,objectMaskTarget);
clsLoss = classConfidenceLoss(YPredCell(:,6),classTarget,objectMaskTarget);
totalLoss = boxLoss + objLoss + clsLoss;

info.boxLoss = boxLoss;
info.objLoss = objLoss;
info.clsLoss = clsLoss;
info.totalLoss = totalLoss;

% Compute gradients of learnables with regard to loss.
gradients = dlgradient(totalLoss, detector.Learnables);
end

function boxLoss = bboxOffsetLoss(boxPredCell, boxDeltaTarget, boxMaskTarget, boxErrorScaleTarget)
% Mean squared error for bounding box position.
lossX = sum(cellfun(@(a,b,c,d) mse(a.*c.*d,b.*c.*d),boxPredCell(:,1),boxDeltaTarget(:,1),boxMaskTarget(:,1),boxErrorScaleTarget));
lossY = sum(cellfun(@(a,b,c,d) mse(a.*c.*d,b.*c.*d),boxPredCell(:,2),boxDeltaTarget(:,2),boxMaskTarget(:,1),boxErrorScaleTarget));
lossW = sum(cellfun(@(a,b,c,d) mse(a.*c.*d,b.*c.*d),boxPredCell(:,3),boxDeltaTarget(:,3),boxMaskTarget(:,1),boxErrorScaleTarget));
lossH = sum(cellfun(@(a,b,c,d) mse(a.*c.*d,b.*c.*d),boxPredCell(:,4),boxDeltaTarget(:,4),boxMaskTarget(:,1),boxErrorScaleTarget));
boxLoss = lossX+lossY+lossW+lossH;
end
function objLoss = objectnessLoss(objectnessPredCell, objectnessDeltaTarget, boxMaskTarget)
% Binary cross-entropy loss for objectness score.
objLoss = sum(cellfun(@(a,b,c) crossentropy(a.*c,b.*c,'TargetCategories','independent'),objectnessPredCell,objectnessDeltaTarget,boxMaskTarget(:,2)));
end

function clsLoss = classConfidenceLoss(classPredCell, classTarget, boxMaskTarget)
% Binary cross-entropy loss for class confidence score.
clsLoss = sum(cellfun(@(a,b,c) crossentropy(a.*c,b.*c,'TargetCategories','independent'),classPredCell,classTarget,boxMaskTarget(:,3)));
end

%%
function data = augmentData(A)
% Apply random horizontal flipping, and random X/Y scaling. Boxes that get
% scaled outside the bounds are clipped if the overlap is above 0.25. Also,
% jitter image color.

data = cell(size(A));
for ii = 1:size(A,1)
    I = A{ii,1};
    bboxes = A{ii,2};
    labels = A{ii,3};
    sz = size(I);

    if numel(sz) == 3 && sz(3) == 3
        I = jitterColorHSV(I,...
            'Contrast',0.0,...
            'Hue',0.1,...
            'Saturation',0.2,...
            'Brightness',0.2);
    end
    
    % Randomly flip image.
    tform = randomAffine2d('XReflection',true,'Scale',[1 1.1]);
    rout = affineOutputView(sz,tform,'BoundsStyle','centerOutput');
    I = imwarp(I,tform,'OutputView',rout);
    
    % Apply same transform to boxes.
    [bboxes,indices] = bboxwarp(bboxes,tform,rout,'OverlapThreshold',0.25);
    labels = labels(indices);
    
    % Return original data only when all boxes are removed by warping.
    if isempty(indices)
        data(ii,:) = A(ii,:);
    else
        data(ii,:) = {I, bboxes, labels};
    end
end
end


function data = preprocessData(data, targetSize)
% Resize the images and scale the pixels to between 0 and 1. Also scale the
% corresponding bounding boxes.

for ii = 1:size(data,1)
    I = data{ii,1};
    imgSize = size(I);
    
    % Convert an input image with single channel to 3 channels.
    if numel(imgSize) < 3 
        I = repmat(I,1,1,3);
    end
    bboxes = data{ii,2};

    I = im2single(imresize(I,targetSize(1:2)));
    scale = targetSize(1:2)./imgSize(1:2);
    bboxes = bboxresize(bboxes,scale);
    
    data(ii, 1:2) = {I, bboxes};
end
end

function [XTrain, YTrain] = createBatchData(data, groundTruthBoxes, groundTruthClasses, classNames)
% Returns images combined along the batch dimension in XTrain and
% normalized bounding boxes concatenated with classIDs in YTrain

% Concatenate images along the batch dimension.
XTrain = cat(4, data{:,1});

% Get class IDs from the class names.
classNames = repmat({categorical(classNames')}, size(groundTruthClasses));
[~, classIndices] = cellfun(@(a,b)ismember(a,b), groundTruthClasses, classNames, 'UniformOutput', false);

% Append the label indexes and training image size to scaled bounding boxes
% and create a single cell array of responses.
combinedResponses = cellfun(@(bbox, classid)[bbox, classid], groundTruthBoxes, classIndices, 'UniformOutput', false);
len = max( cellfun(@(x)size(x,1), combinedResponses ) );
paddedBBoxes = cellfun( @(v) padarray(v,[len-size(v,1),0],0,'post'), combinedResponses, 'UniformOutput',false);
YTrain = cat(4, paddedBBoxes{:,1});
end

%%
function currentLR = piecewiseLearningRateWithWarmup(iteration, epoch, learningRate, warmupPeriod, numEpochs)
% The piecewiseLearningRateWithWarmup function computes the current
% learning rate based on the iteration number.
persistent warmUpEpoch;

if iteration <= warmupPeriod
    % Increase the learning rate for number of iterations in warmup period.
    currentLR = learningRate * ((iteration/warmupPeriod)^4);
    warmUpEpoch = epoch;
elseif iteration >= warmupPeriod && epoch < warmUpEpoch+floor(0.6*(numEpochs-warmUpEpoch))
    % After warm up period, keep the learning rate constant if the remaining number of epochs is less than 60 percent. 
    currentLR = learningRate;
    
elseif epoch >= warmUpEpoch + floor(0.6*(numEpochs-warmUpEpoch)) && epoch < warmUpEpoch+floor(0.9*(numEpochs-warmUpEpoch))
    % If the remaining number of epochs is more than 60 percent but less
    % than 90 percent multiply the learning rate by 0.1.
    currentLR = learningRate*0.1;
    
else
    % If remaining epochs are more than 90 percent multiply the learning
    % rate by 0.01.
    currentLR = learningRate*0.01;
end

end

function [lossPlotter, learningRatePlotter] = configureTrainingProgressPlotter(f)
% Create the subplots to display the loss and learning rate.
figure(f);
clf
subplot(2,1,1);
ylabel('Learning Rate');
xlabel('Iteration');
learningRatePlotter = animatedline;
subplot(2,1,2);
ylabel('Total Loss');
xlabel('Iteration');
lossPlotter = animatedline;
end

function displayLossInfo(epoch, iteration, currentLR, lossInfo)
% Display loss information for each iteration.
disp("Epoch : " + epoch + " | Iteration : " + iteration + " | Learning Rate : " + currentLR + ...
   " | Total Loss : " + double(gather(extractdata(lossInfo.totalLoss))) + ...
   " | Box Loss : " + double(gather(extractdata(lossInfo.boxLoss))) + ...
   " | Object Loss : " + double(gather(extractdata(lossInfo.objLoss))) + ...
   " | Class Loss : " + double(gather(extractdata(lossInfo.clsLoss))));
end

function updatePlots(lossPlotter, learningRatePlotter, iteration, currentLR, totalLoss)
% Update loss and learning rate plots.
addpoints(lossPlotter, iteration, double(extractdata(gather(totalLoss))));
addpoints(learningRatePlotter, iteration, currentLR);
drawnow
end

function detector = downloadPretrainedYOLOv3Detector()
% Download a pretrained yolov3 detector.
if ~exist('yolov3SqueezeNetVehicleExample_21aSPKG.mat', 'file')
    if ~exist('yolov3SqueezeNetVehicleExample_21aSPKG.zip', 'file')
        disp('Downloading pretrained detector...');
        pretrainedURL = 'https://ssd.mathworks.com/supportfiles/vision/data/yolov3SqueezeNetVehicleExample_21aSPKG.zip';
        websave('yolov3SqueezeNetVehicleExample_21aSPKG.zip', pretrainedURL);
    end
    unzip('yolov3SqueezeNetVehicleExample_21aSPKG.zip');
end
pretrained = load("yolov3SqueezeNetVehicleExample_21aSPKG.mat");
detector = pretrained.detector;
end