Detect objects using SSD multibox object detector
detects objects within a single image or an array of images,
bboxes = detect(
an single shot multibox detector (SSD). The locations of objects detected are returned as
a set of bounding boxes.
When using this function, use of a CUDA® enabled NVIDIA® GPU with a compute capability of 3.0 or higher is highly recommended. The GPU reduces computation time significantly. Usage of the GPU requires Parallel Computing Toolbox™.
[___] = detect(___,
detects objects within the rectangular search region specified by
[___] = detect(___,
specifies options using one or more
Name,Value pair arguments. For
detect(detector,I,'Threshold',0.75) sets the detection score
0.75. Any detections with a lower score are
Load a pretrained single shot detector (SSD) object to detect vehicles in an image. The detector is trained with images of cars on a highway scene.
vehicleDetector = load('ssdVehicleDetector.mat','detector'); detector = vehicleDetector.detector;
Read a test image into the workspace.
I = imread('highway.png');
Display the test image.
Run the pretrained SSD object detector by using the
detect function. The output contains the bounding boxes, scores, and the labels for vehicles detected in the image. The labels are derived from the
ClassNames property of the detector.
[bboxes,scores,labels] = detect(detector,I)
bboxes = 2×4 139 78 96 81 99 67 165 146
scores = 2x1 single column vector 0.8349 0.6302
labels = 1x2 categorical vehicle vehicle
Annotate the image with the detection results.
if ~isempty(bboxes) detectedI = insertObjectAnnotation(I,'rectangle',bboxes,cellstr(labels)); else detectedI = insertText(I,[10 10],'No Detections'); end figure imshow(detectedI)
I— Input image
Input image, specified as an H-by-W-by-C-by-B numeric array of images Images must be real, nonsparse, grayscale or RGB image.
C: The channel size in each image must be equal to
the network's input channel size. For example, for grayscale images,
C must be equal to
1. For RGB
color images, it must be equal to
B: The number of images in the array.
The detector is sensitive to the range of the input image. Therefore, ensure that the input
image range is similar to the range of the images used to train the detector. For
example, if the detector was trained on
uint8 images, rescale
this input image to the range [0, 255] by using the
rescale function. The size of this input image should be comparable
to the sizes of the images used in training. If these sizes are very different, the
detector has difficulty detecting objects because the scale of the objects in the
input image differs from the scale of the objects the detector was trained to
identify. Consider whether you used the
property during training to modify the size of training images.
Datastore, specified as a datastore object containing a collection of images. Each image must be a grayscale, RGB, or multichannel image. The function processes only the first column of the datastore, which must contain images and must be cell arrays or tables with multiple columns.
roi— Search region of interest
Search region of interest, specified as an [x y width height] vector. The vector specifies the upper left corner and size of a region in pixels.
comma-separated pairs of
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
'Threshold'— Detection threshold
0.5(default) | scalar
Detection threshold, specified as a scalar in the range [0, 1]. Detections that have scores less than this threshold value are removed. To reduce false positives, increase this value.
'SelectStrongest'— Select strongest bounding box
Select the strongest bounding box for each detected object, specified as the
comma-separated pair consisting of
'SelectStrongest' and either
true — Return the strongest bounding box per object. To
select these boxes,
detect calls the
selectStrongestBboxMulticlass function, which uses nonmaximal
suppression to eliminate overlapping bounding boxes based on their confidence
selectStrongestBboxMulticlass(bbox,scores, ... 'RatioType','Min', ... 'OverlapThreshold',0.5);
false — Return all detected bounding boxes. You can then
create your own custom operation to eliminate overlapping bounding boxes.
'MaxSize'— Maximum region size
I) (default) | [height width] vector
Maximum region size that contains a detected object, specified as the
comma-separated pair consisting of
'MaxSize' and a
width] vector. Units are in pixels.
To reduce computation time, set this value to the known maximum region size for
the objects being detected in the image. By default,
set to the height and width of the input image,
'MiniBatchSize'— Minimum batch size
128(default) | scalar
Minimum batch size, specified as the comma-separated pair consisting of
'MiniBatchSize' and a scalar value. Use the
MiniBatchSize to process a large collection of images. Images
are grouped into minibatches and processed as a batch to improve computation
efficiency. Increase the minibatch size to decrease processing time. Decrease the size
to use less memory.
'ExecutionEnvironment'— Hardware resource
Hardware resource on which to run the detector, specified as the comma-separated
pair consisting of
'auto' — Use a GPU if it is available. Otherwise, use the
'gpu' — Use the GPU. To use a GPU, you must have
Parallel Computing Toolbox and a CUDA enabled NVIDIA GPU with a compute capability of 3.0 or higher. If a suitable GPU
is not available, the function returns an error.
'cpu' — Use the CPU.
bboxes— Location of objects detected
Location of objects detected within the input image or images, returned as an M-by-4 matrix or a B-by-1 cell array. M is the number of bounding boxes in an image, and B is the number of M-by-4 matrices when the input contains an array of images.
Each row of
bboxes contains a four-element vector of the
height]. This vector specifies the upper left corner and size
of that corresponding bounding box in pixels.
scores— Detection scores
Detection confidence scores, returned as an M-by-1 vector or a B-by-1 cell array. M is the number of bounding boxes in an image, and B is the number of M-by-1 vectors when the input contains an array of images. A higher score indicates higher confidence in the detection.
labels— Labels for bounding boxes
Labels for bounding boxes, returned as an M-by-1 categorical array or a
B-by-1 cell array. M is the number of
labels in an image, and B is the number of
M-by-1 categorical arrays when the input contains an
array of images. You define the class names used to label the objects when you
train the input
detectionResults— Detection results
Detection results, returned as a 3-column table with variable names, Boxes, Scores, and Labels. The Boxes column contains M-by-4 matrices, of M bounding boxes for the objects found in the image. Each row contains a bounding box as a 4-element vector in the format [x,y,width,height]. The format specifies the upper-left corner location and size in pixels of the bounding box in the corresponding image.