MATLAB: How to find the change in curve

digital signal processingimage processingImage Processing Toolbox

i have plotted a curve on my image. The curve is shown in red. I want to find the jump in my curve with some good algroithm. The area in the curve where i want to detect jump is shown in blue. I have tried to find difference between two point to detect jump but that always does not return me the points in the curve i want(show in blue).

Best Answer

Have you tried findchangepts()?

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MATLAB: Fitting curve to points in image

Use bwconvhull(), then followup with bwboundaries().

MATLAB: How to get the coordinate of this four points

Here's another approach which works with the clean image you've given us. It's not as neat as Matt's approach, but it includes some techniques that you might find helpful when you're working with your more difficult camera images.

The core of this approach is a pair of morphological dilations which merge the bars into each other to form a large rectangular block. It depends on knowing the orientation of the bars, at least approximately.

imraw = imread('2ebx0t2.gif'); % dowloaded image
img = imraw < max(imraw(:));   % binarized
masklen = 21;                  % max bar spacing in pixels
lmask = zeros(1, masklen);     % mask to smear pixels to right
lmask(ceil(end/2):end) = 1;    
rmask = fliplr(lmask);         % mask to smear pixels to left
block = imdilate(img, lmask) & imdilate(img,rmask);  % smear pixels sideways
rprops = regionprops(block, 'BoundingBox', 'Area');  % get measurements
[~, bigblock] = max([rprops.Area]);     % select largest block
bbox = rprops(bigblock).BoundingBox;    % and get its bounding box
cornersx = bbox([1 1 1 1]) + [0 bbox([3 3]) 0];  % rearrange to get coords
cornersy = bbox([2 2 2 2]) + [0 0 bbox([4 4])];
imshow(imraw, []);              % display image
hold on; plot(cornersx, cornersy, 'b+'); hold off; % with corner coordinates

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MATLAB: Fitting curve to points in image

MATLAB: How to get the coordinate of this four points

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