Mapping bounding box to the original image

Hi, i have a real time skin detection algorithm where it gives me a bounding box around the skin region with rectangle('Position',bb,'EdgeColor','r','LineWidth',2) from an original image. I wish to use the code to first detect the skin region from the original image before i use Viola Jones to detect the face region from the cropped skin region. I wish to know after i crop the skin region then use the face detection algorithm to detect the face, how can i map the bounding box of the face to the original image .

The code for skin detection and VJ face detection is as below for those who want to know.

function cameraon_Callback(hObject, eventdata, handles)
% hObject    handle to cameraon (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
global video;
global videoFrame;
axes(handles.axes1);
video = videoinput('winvideo',1,'YUY2_320x240');
set(video,'ReturnedColorSpace','rgb');
handles.video=video;
triggerconfig(video,'manual');
video.FramesPerTrigger = 1;
guidata(hObject,handles);

faceDetector=vision.CascadeObjectDetector('FrontalFaceCART');
faceDetector.MinSize=[20 20];
faceDetector.MergeThreshold = 20;
videoFrame=getsnapshot(video);
bbox=step(faceDetector,videoFrame);
 if numel(bbox) == 0
    errordlg('Face not detected. Please try again.');
    set(handles.cameraon,'String','Start Camera')
    stop(video);
    delete(video);
    clear;
else
     axes(handles.axes1);
     start(video);
end

while(true)
    frame=getsnapshot(video);
%Detect faces.
data = frame;% this is to read a image from data base. just put any image name u want to give make sure its placed in bin

diff_im = imsubtract(data(:,:,1), rgb2gray(data)); % deleting gray scale pixels from image

diff_im = medfilt2(diff_im, [3 3]); %applying filter one 

diff_im = imadjust(diff_im); % adjust image function to fill small holes (check all the function's functionality to have idea of whats going on)
level = graythresh(diff_im);% extract level value

bw = im2bw(diff_im,level);
BW5 = imfill(bw,'holes');
bw6 = bwlabel(BW5, 8);
stats = regionprops(bw6,['basic']);%basic mohem nist

measurements = regionprops(bw6, 'boundingbox');
BB1=struct2cell(measurements);
BB2=cell2mat(BB1);
a = BB2(1);
b = BB2(2);
c = BB2(3);
d = BB2(4);
[N,M]=size(stats);

if (bw==0)% check if there is no skin color then exit
        break;
else
     tmp = stats(1);

for i = 2 : N % checking for biggest hole to mark it as face 
      if stats(i).Area > tmp.Area
        tmp = stats(i);
      end
 end

bb = tmp.BoundingBox; % applying identification square to mark skin color region
bc = tmp.Centroid;

   videoFrame=getsnapshot(video);

This is the place where i cannot put the bounding box back to the original image.

   skinImage    = imcrop(videoFrame,bb(1,:));

    bbox = step(faceDetector,skinImage);
  bbox(1,1:2) = bbox(1,1:2) + bb(1,1:2);
      videoOut = insertObjectAnnotation(videoFrame,'rectangle',bbox,'Face'); 

    cla;
    imshow(videoOut,[]);

    drawnow;
    pause(0.0001);
  end
  end
  guidata(hObject,handles);

Answer 1

[Image Analyst]

Why do you think that regionprops does not return bounding box coordinates in the coordinate system of the image you passed to it? It will.

By the way, please read this and fix your post: http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup

[Jia Zhen]

Hi, i know regionprop will give me the bounding box coordinate. However i did not know how to put the cropped image back to the original position in the original image. I had already put the whole coding above and also highlighted the place which i am getting the error.

[Image Analyst]

I still don't understand. The cropped image already IS in the original image - that's where it came from. And your call to insertObjectAnnotation() should put a rectangle in the overlay above the full size image at the original location in the image where the cropped image came from. You just have to pass it bbox + bb(1,:) to put back in the offset.

[Jia Zhen]

Yes that is what i mean. I want to put the rectangle i got from the face detector onto the full size image at the original location in the image where the cropped image come from. Do you mean it is

videoOut = insertObjectAnnotation(videoFrame,'rectangle',bbox + bb(1,:),'Face');

?

[Image Analyst]

Yes. Anyway, it's easy enough to try.

[Jia Zhen]

Hi, sorry to bother you again but i am having this error for

videoOut = insertObjectAnnotation(videoFrame,'rectangle',bbox + bb(1,:),'Face'); 

Error using  + 
Matrix dimensions must agree.

Error in realtime4>cameraon_Callback (line 153)
    videoOut = insertObjectAnnotation(videoFrame,'rectangle',bbox +
    bb(1,:),'Face');

When i change

bbox(1,1:2) = bbox(1,1:2) + bb(1,1:2);

to

bbox = bbox + bb(1,:);

i still get this error

Error using + Matrix dimensions must agree.

Error in realtime4>cameraon_Callback (line 153) bbox = bbox + bb(1,:);

[Image Analyst]

Just try putting everything into single variables like x,y,width, and height, or row1, row2, col1, col2. Then examine what they are, and what makes sense - what they should be. I'm sure you can figure it out then.