Detect irregular dark spots in a gray scale image.

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Meghana Dinesh
Meghana Dinesh on 6 Nov 2015
Commented: Meghana Dinesh on 13 Nov 2015
I require ideas to detect these kind of black spots in a gray scale image.
I have tried applying Canny and Sobel edge detectors (with various thresholds) but didn't get good results. There's a lot of noise.
Visually, there's stark difference between the bottle and the black hole. But the log filter output doesn't show this high difference. Moreover, only the small boundary around the hole is detected. (FYI: the drop kind of shape on the left shouldn't be detected since it's not a defect.)
Is there any other method I can use?
I have attached the gray scale image.
This is the output of imadjust(GrayImg). What function can I use to find the encircled regions?
Kindly note that I am able to segment the bottle. So basically, I am ignoring the top and bottom 300 rows, and left and right 100 columns in all images.

Answers (1)

Image Analyst
Image Analyst on 9 Nov 2015
First of all, make a mask that includes only the bottle but not the "okay" region at the left of it. Then run a texture filter over the masked image, like stdfilt(). Then threshold.
Meghana Dinesh
Meghana Dinesh on 13 Nov 2015
I have tried the Texture Analysis functions ( rangefilt, stdfilt and entropyfilt ) with different NHOOD matrices.
When I used CLAHE ( adapthisteq ), I found that the drop shape also gets highlighted.
Till now, the best method for my case has been LOG filter:
filt_img = imfilter(GrayImg_dbl, fspecial('log',31,5));
This does not detect the small black pinhole though.

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