Matlab-使用逻辑索引删除图像边框

Question

I have a retinal fundus image which has a white border along the corners. I am trying to remove the borders on all four sides of the image. This is a pre-processing step and my image looks like this:

fundus http://snag.gy/XLGkC.jpg

It is an RGB image, and I took the green channel, and created a mask using logical indexing. I searched for pixels which were all black in the image, and eroded the mask to remove the white edge pixels. However, I am not sure how to retrieve the final image, without the white pixel border using the mask that I have. This is my code, and any help would be appreciated:

maskIdx = rgb(:,:,2) == 0;   # rgb is the original image
se = strel('disk',3);        # erode 3-pixel using a disk structuring element 
im2 = imerode(maskIdx, se);
newrgb = rgb(im2);           # gives a vector - not the same size as original im

Answer 1

Solved it myself. This is what I did with some help.

I first computed the mask for all three color channels combined. This is because the mask for each channel is not the same when applied to all the three channels individually, and residual pixels will be left in the final image if I used only the mask from one of the channels in the original image:

mask = (rgb(:,:,1) == 0) & (rgb(:,:,2) == 0) & (rgb(:,:,3) == 0);

Next, I used a disk structuring element with a radius of 9 pixels to dilate my mask:

se = strel('disk', 9); 
maskIdx = imdilate(mask,se);

EDIT: A structuring element which is arbitrary can also be used. I used: se = strel(ones(9,9))

Then, with the new mask, I multiplied the original image with the new dilated mask:

newImg(:,:,1) = rgb(:,:,1) .* uint8(maskIdx);    # image was of double data-type
newImg(:,:,2) = rgb(:,:,2) .* uint8(maskIdx);
newImg(:,:,3) = rgb(:,:,3) .* uint8(maskIdx);

Finally, I subtracted the computed color-mask from the original image to get my desired border-removed image:

finalImg = rgb - newImg;

Result:

image http://snag.gy/g2X1v.jpg