Automatic curve extraction from image

Hi everybody.

I have a series of images like this:

How can I remove background of this image automatically and extract the curves which is shown in the following image?

The output image must be binary. simple thresholding doesn't work.

Answer 1

[Image Analyst]

I'd threshold the image to get a mask, then scan across column by column getting the first row and last row. Something like

mask = grayImage > someThreshold;
[rows, columns] = size(mask);
topRows = nan(1, columns);
bottomrows = nan(1, columns);
for col = 1 : columns
    t = find(mask(:, col), 1, 'first');
    if ~isempty(t)
        topRows(col) = 1;
        bottomRows(col) = find(mask(:, col), 1, 'last');
    end
end
hold on;
plot(topRows, 'w-', 'LineWidth', 5);
plot(bottomRows, 'n-', 'LineWidth', 5);

adapt as needed.

If you really can't figure it out, then attach your original image (not a screenshot with tickmarks, etc.).

[rastak rastaki]

hi dear image analyst.

first of all thanks for your fast response. I applied your code to my image and the result is like this:

The result strongly depends on the threshold value. I used 0.2 of max value. As you can see, because of noisey-like pattern between up and buttom curvs, the result is not as good.

Thanks any way.