Image processing and contour detection

With respect to the image below, how can I detect the the upper (red) and lower (green) contour on the boundaries shown n the image below. Also, how do I calculate the distance between the two boundaries (blue)?

Answer 1

[Sachin]

Hi

I understand that you want to find the contours in the image.

I suggest you to use Image processing and Computer Vision Toolbox. The toolbox provides two functions -

1. ‘bwboundaries' – This function is used to compute the boundary of a binary image . It takes a binary image as input and computes the boundary of the connected region in the binary image
2. ‘bwtraceboundary’ – This function is used to trace a boundary in a binary image.It takes a binary image as input and a starting point on the boundary and trace the boundary of the connected region in the image.

These function provides boundary coordinates that can be used find the distance between two points

grayImage = rgb2gray(image);

threshold = 50; % Set threshold value
binaryImage = grayImage > threshold;

boundaries = bwboundaries(binaryImage);
imshow(image);
hold on;
for k = 1:length(boundaries)
    boundary = boundaries{k};
    plot(boundary(:,2), boundary(:,1), 'b', 'LineWidth', 2);
end

If you encounter any issues with these functions, you can also use OpenCV library to find contours.

Please refer the following page for more information about boundary function:

https://www.mathworks.com/help/images/boundary-tracing-in-images.html

Please refer OpenCV documentation for more information on finding contours

https://docs.opencv.org/3.4/d4/d73/tutorial_py_contours_begin.html

[KATHAN BHAVSAR]

Thank you, I will certainly try this out.

Answer 2

[Image Analyst]

To find average width of a blob, see attached demo.