How can I fix 'index ecxeeds matrix dimension' in face detection?

hello, I've been working out with this coding which is if face have been detected, the ultrasonic can be sensed. Supposedly when the face not detected, the ultrasonic cannot be sensed.

%Create a detector object
faceDetector = vision.CascadeObjectDetector;

%Read input image from webcam
obj = imaq.VideoDevice('winvideo',1,'YUY2_160x120');
set(obj,'ReturnedColorSpace','rgb');

a = arduino('COM9', 'Uno', 'Libraries', {'JRodrigoTech/HCSR04', 'Servo'});
sensor = addon(a, 'JRodrigoTech/HCSR04','D12','D13');
servo_motor = servo(a,'D7');

%preview(obj)
axes(handles.axes1)
while(true)
frame=step(obj);
%Detect faces
bboxes =step(faceDetector,frame); 
    if bboxes (true)
    %Annotate detected faces
    IFaces = insertObjectAnnotation(frame,'rectangle', bboxes, 'HumanFace');
    imshow(IFaces)  
    for i=1:inf
  dist1=readDistance(sensor);   
  if(dist1<0.1500)
        writePosition(servo_motor, 0.4);
        cp = readPosition(servo_motor);
        cp = cp*180;
        fprintf('LID OPEN\n');
        pause(5)  
       break
  else
        fprintf('LID CLOSE\n');
        break
end
writePosition(servo_motor, 0);
cp = readPosition(servo_motor);
cp = cp*180
fprintf('LID CLOSE\n');
    end

   else(isempty(bboxes))
      fprintf('LID CLOSE\n');
   end
  end
  %closepreview(obj)
  release(obj)

The ultrasonic sensor and servo motor is working well. But when I try to not show my face, the coding will show 'index exceeds matrix dimension' and error at 'if bboxes(true)'. Can someone tell me where the wrong part in my coding?

Answer 1

[Walter Roberson]

You have

bboxes =step(faceDetector,frame); 
if bboxes (true)

When bboxes is not empty, then the equivalent code is:

temp = false(size(bboxes));
temp(1) = true;
if bboxes(temp) ~= 0

which uses logical indexing to select the first element of bboxes and then test whether it is zero or not. This works out to be the same as

if bboxes(1) ~= 0

Now consider the case where bboxes is empty because nothing was detected. Then bboxes(true) tries to select the first element of bboxes, same as bboxes(1), and that is a problem because bboxes is empty.

If what you want to check is whether any bounding boxes were detected, then your check should be

if ~isempty(bboxes)

[amira janna]

Thank you sir! Glad that you solve my problem