Detecting a specific line in an image

Hello,

I have several images and I need to detect a profile that it changes on time. The images are grey colours and the constrast is not great in the area that I want to detect the edge.

I have tried several ways and methods (e.g. thresholder filter, using all methods with 'edge', changing the LUT in the image etc etc).

Any suggestions?

I have included an example of the image and the line that I would like to detect. The line is clear to my eye but I cannot get a script to detect it.

I would really appreciate your help!

Thanks

Answer 1

[Pranav Verma]

Hi Paloma,

You can try using the basic image segmentation method for the line detection if the methods you specified are not working for you.

The image processing toolbox in MATLAB has specific functionalities for image segmentation. Please refer to the below link for the same:

Image segmentation

Thanks

[paloma paleo]

I have already tried using the different methods for image segmentation but it doesnt work. I am not getting the line that I am looking for.

Answer 2

[paloma paleo]

I have tried several ways (see code below) but I am not getting any good results.

close all

% Read in image and the image info

I = imread('Img000000.tif');

I = I(:,:,1);

option=2; %option 1 sobel

%option 2 segmentation

if option==1

%Sobel Edge filter

BW = edge(I,'Sobel',0,'both');

imtool(BW)

[H,theta,rho] = hough(BW);

P = houghpeaks(H,5,'threshold',ceil(0.3*max(H(:))));

x = theta(P(:,2));

y = rho(P(:,1));

% plot(x,y,'s','color','black');

lines = houghlines(BW,theta,rho,P,'FillGap',5,'MinLength',7);

imshow(BW)

figure, imshow(I), hold on

%Extract endpoints from individual hough lines

points = [];

for k = 1:length(lines)

points = [points; lines(k).point1; lines(k).point2];

end

% Fit overall line from individual lines from hough

x1 = 1:size(I,2);

p = polyfit(points(:,1),points(:,2),1);

y1 = polyval(p,x1);

plot(x1,y1,'r','LineWidth',3)

end

if option==2

% option 2.1

% level = graythresh(I);

%

% BW = imbinarize(I,level);

% imshowpair(I,BW,'montage')

% option 2.2

% level = multithresh(I);

% seg_I = imquantize(I,level);

% figure

% imshow(seg_I,[])

% option 2.3

% [counts,x] = imhist(I,16);

% stem(x,counts)

% % figure(1), plot(x,counts)

% T = otsuthresh(counts);

% BW = imbinarize(I,T);

% figure

% imshow(BW)

% option 2.4 - best

% T = adaptthresh(I, 0.75);

% BW = imbinarize(I,T);

% figure

% imshowpair(I, BW, 'montage')

% option 2.5

%

% J = grayconnected(I,184,30);%choose the x,y values of the seed intesity

% imshow(labeloverlay(I,J))

% option 2.6

%

% mask = zeros(size(I));

% %mask(25:end-25,25:end-25) = 1;

% mask(:,60:end-850) = 1;

% %imshow(mask)

% %title('Initial Contour Location')

% bw = activecontour(I,mask,50);

% imshow(bw)

% title('Segmented Image, 300 Iterations')

% option 2.7

%

% RGB=I;

% L = superpixels(RGB,500);

%

% figure(1)

% imshow(I)

%

% %roi = drawrectangle %provides the coord info of the rectangular draw using

% %the mouse

% f = drawrectangle(gca,'Position',[65 0 120 1020],'Color','g');

%

% foreground = createMask(f,RGB);

% b1 = drawrectangle(gca,'Position',[217.1442 8.7460 203.9004 1.0158e+03],'Color','r');

% b2 = drawrectangle(gca,'Position',[0.5000 2.7489 75.7130 1.0218e+03],'Color','r');

% background = createMask(b1,RGB) + createMask(b2,RGB);

%

% BW = lazysnapping(RGB,L,foreground,background);

% imshow(labeloverlay(RGB,BW,'Colormap',[0 1 0]))

%option 2.8

%mask(:,60:end-850) = 1

% mask = false(size(I));

% mask(30,170) = true;

%

%

% W = graydiffweight(I, mask, 'GrayDifferenceCutoff',1000);

%

% thresh = 0.009;

% [BW, D] = imsegfmm(W, mask, thresh);

% figure

% imshow(BW)

% title('Segmented Image')

%

%

%

%

%

% imshow(I)

% title('Original Image')

% seedpointR = 72;

% seedpointC = 100;

% W = graydiffweight(I, seedpointC, seedpointR,'GrayDifferenceCutoff',250);

% figure (23), imshow(log(W))

% thresh = 0.0001;

% [BW, D] = imsegfmm(W, mask, thresh);

% figure (55)

% imshow(BW)

% title('Segmented Image')

% Ifil=medfilt2(BW, [5 5]);

% imtool(Ifil)

end