Odd Outcome From imerode and bwlabel

Hello,

I am trying to program a shape placement algorithm using image processing in Matlab.

The algorithm should place images of shapes on a larger background image in a way that minimizes the wasted background. I am using imerode to erode the current background image with the bounding box of the shape to be placed as the structuring element. Thus, imerode should return an image with 1's everywhere where the origin of the structuring element can be placed so that it is entirely contained within the background image. Imerode does this correctly. However, when I use bwlabel on the image returned from erosion for further processing, an image of the structuring element appears in the bottom left corner. I don't understand why this is happening. I'm sure it would help to see the images that I am refering to but I don't think pictures can be attached to this question. Can anyone explain please? Any help would be greatly appreciated. Thank you.

[Sean de Wolski]

Use a free image hosting website and give us the link. Also, post the code and use formatting so we can see what MATLAB is _actually_ doing.

http://www.mathworks.com/matlabcentral/answers/7924-where-can-i-upload-images-and-files-for-use-on-matlab-answers

[Sean de Wolski]

Welcome to MATLAB Answers!

Answer 1

[ssklios Sklios]

Thank you so much for responding. Here are examples of the images in question:

1. http://i1127.photobucket.com/albums/l633/seansklios/background.jpg (this is the background image)

2. http://i1127.photobucket.com/albums/l633/seansklios/structuringelement.jpg (this is the structuring element)

3. http://i1127.photobucket.com/albums/l633/seansklios/erodedimage.jpg (this is the eroded image)

4. http://i1127.photobucket.com/albums/l633/seansklios/bwlabeloferodedimage.jpg (this is the eroded image after bwlabel)

Notice the strange image in the bottom right of the bwlabel image. I will upload some of the code shortly. Thanks again!

Answer 2

[ssklios Sklios]

Here is the part of my code that has to do with imerode. currentpart is an image of a shape to be placed and current scene is the background that the shape has to be placed on. I first rotate the shape image to align with the background. Then make the structuring element the image of the bounding box of the shape. Then erode the structuring element into the current scene.

%rotate    
partrot=RotObject(currentpart,angles(b));
partrot=bwlabel(partrot);   
partstats=regionprops(partrot,'BoundingBox','Image');

%Extend current scene
bb=minBoundingBox(partrot);
LH=lengthheight(bb);
L=LH(1);
H=LH(2);
currentscene(1,1)=currentscene(1,1)+H*cos(backanglerads-pi/2)+L*cos(backanglerads);
currentscene(1,2)=currentscene(1,2)+H*sin(backanglerads-pi/2)+L*sin(backanglerads);
currentscene(2,1)=currentscene(2,1)+H*cos(backanglerads-pi/2);
currentscene(2,2)=currentscene(2,2)+H*sin(backanglerads-pi/2);
currentscene(4,1)=currentscene(4,1)+L*cos(backanglerads);
currentscene(4,2)=currentscene(4,2)+L*sin(backanglerads);
[r c]=size(fullscene);
M = poly2mask(currentscene(:,1), currentscene(:,2), r, c);
currentscene=immultiply(M,fullscene);

%Make structuring element
S=strel(partstats.Image);
strelcent=floor((size(partstats.Image)+1)/2);
boxcent=[partstats.BoundingBox(2)+strelcent(1) partstats.BoundingBox(1)+strelcent(2)];

%make placement   
pos=imerode(currentscene,S);
posL= bwlabel(pos')';