Is there a way to get a "thicker" bwconncomp connection?

See attached image. I have a stack of similar images and I want to remove the large white spaces on the top, bottom, and left of the image.

I used the code:

CC = bwconncomp(BW)
numPixels = cellfun(@numel,CC.PixelIdxList);
[biggest,idx] = max(numPixels);
BW(CC.PixelIdxList{idx}) = 0;

but this sets almost the entire picture black. I suspect it is because there is a little touching between the whites, I want matlab to only pick up the obvious white spaces on the sides. What am i doing wrong?

[Gopichandh Danala]

can you upload the original image

Answer 1

[Gopichandh Danala]

If you are just trying to replace all the white pixels in the surroundings to 0, all the connected white valleys on the edges also get removed.

img = rgb2gray(imread('image.png'));
BW = bwlabel(img); % based on labelling algorithm the left top is '1' so backgrounf label is '1'
img(BW == 1) = 0; % replace this label pixels in image to 0  
figure, imshow(img);