Edge detection and cropping out region of higer intensity of Grayscale images

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Colin Ng
Colin Ng 2015-6-24
评论： Colin Ng 2015-6-26
Hi all,
Please find attached image that I am working on. The region of interest that I intend to crop out (and to keep values of x & y )is shown to be the parabolic fluid profile of higher intensity than its background.
I have tried Edge of 'zero crossing' and 'canny', which are able to standout the ROI by slightly. I am however more interested in a total cropping of the ROI leaving all background as 0 in binary. I suppose my images are not like most of the examples used for edge where there is a clear distinction/ continuous distinction between edges, rather mine are dotted. I came across someone else did a median filter then a std deviation filter then only "canny" edge.
I have been able to use improfile to have a look at those intensities values, and the first and the last peak across the X -direction marks the boundary of the ROI.
I could it dot or outline the interface manually using data cursor, but it is definitely not ideal. I could it for just 1 frame manually, however not with a moving interface with each frame.
Please advice what others method should I try or use? Much appreciated for any inputs or assistance.
Colin
  2 个评论
Colin Ng
Colin Ng 2015-6-26
Hi Mukul,
Thanks for the response.
I came across this error when running through your code.
Undefined function 'bwareafilt' for input arguments of type 'double'.
I have also tried other 'bwareafilt' stock example which is available online, to no avail. I have image processing toolbox ver 9.0 with Matlab R2014a installed.
Your code seems fine to me, I am sure I just needed to get the function sorted. Thanks, Colin
Image Analyst
Image Analyst 2015-6-26
bwareafilt() is a fairly new addition to the Image Processing Toolbox - you must have an old version. I am almost an expert in image processing (at least I'm still trying after 36 years of doing nothing else but image processing), but I can't do much with your stuff because your BMP image is corrupted (it says so when I click on it) and you forgot to attach your script.

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Mukul Rao
Mukul Rao 2015-6-25
Hi , I am no expert in image processing but here is what I came up with after playing around with some of the tools, I hope this helps! I believe the method I have used should be evident from the commands and code comments:
%Read the image
I = imread('1405ExpIP20895.bmp');
%Convert to binary based on a threshold
BW = im2bw(I, 0.1);
%Improve connectivity
fillBW = imfill(BW,'holes');
%Select the largest object
BWfilt = bwareafilt(fillBW,1,'largest');
figure
imshow(BWfilt)
%Smoothen the boundaries
BWfinal = imopen(BWfilt, strel('disk',9));
figure
imshow(BWfinal)
%Index into original image
I(~BWfinal) = 0;
figure
imshow(I)
  2 个评论
Colin Ng
Colin Ng 2015-6-26
To update on my situation, I tried it on 2011b and 2014a, bwareafilt still can't be loaded. I have then tried it out with 2015a, and it is working fine.
I am trying to fine tune the process, as some of the images are not being cropped out appropriately. Thanks for your help, Mukul.
Colin
Colin Ng
Colin Ng 2015-6-26
Hi Mukul,
I have had some success with your code, thanks again. These 2 images attached show that some region could not be cropped out as per desired. It is to do with the imfill function, I believe. Maybe it needs some kind of manual intervention. I am looking into imfill.

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