extract strong light-dark transitions in the image by applying a threshold operation to the gradient strength and considering only negative gradients in matlab

To extract strong light-dark transitions in an image by applying a threshold operation to the gradient strength and considering only negative gradients in MATLAB, we can follow these steps:

1. Load the image using the imread function

main.m
img = imread('image.jpg');
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2. Convert the image to grayscale using the rgb2gray function

main.m
gray_img = rgb2gray(img);
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3. Apply the sobel operator to the grayscale image to obtain the gradient magnitude and direction

main.m
[Gmag, Gdir] = imgradient(gray_img, 'sobel');
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4. Set all positive gradients to zero, leaving only the negative gradients

main.m
negative_gradients = Gmag;
negative_gradients(Gmag > 0) = 0;
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5. Apply a threshold operation to the negative gradient strength

main.m
threshold_value = 50;
binary_image = negative_gradients < threshold_value;
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Now, the resulting binary image will have 1s in areas where there are strong light-dark transitions that satisfy the condition of having a negative gradient strength below the threshold value 50, and 0s elsewhere.