Extract one object from bunch of objects and detect edges

Question

For my college project I need to identify a species of a plant from plant leaf shape by detecting edges of a leaf. (I use OpenCV 2.4.9 and C++), but the source image has tak

Answer 1

Well there is a similar question that was asked here:

• opencv matching edge images

It seems that edge information is not a good descriptor for the image, still if you want to try it I'll do the following steps:

1. Load image and convert it to grayscale
2. Detect edges - Canny, Sobel try them and find what it suits you best
3. Set threshold to a given value that eliminates most background - Binarize image
4. Close the image - Morphological close dont close the window!
5. Count and identify objects in the image (Blobs, Watershed)
6. Check each object for a shape (assuming you have described shapes of the leaf you could find before or a standard shape like an ellipse) features like:
   • http://docs.opencv.org/modules/imgproc/doc/structural_analysis_and_shape_descriptors.html
   • http://www.math.uci.edu/icamp/summer/research_11/park/shape_descriptors_survey.pdf
7. If a given object has a given shape that you described as a leaf then you detected the leaf!.

I believe that given images are taken in the real world these algorithm will perform poorly but it's a start. Well hope it helps :).

-- POST EDIT 06/07

Well since you have no prior information about the leaf, I think the best we could do is the following:

• Load image
• Bilateral filter
• Canny
• Extract contours
• Assume: that the contour with the largest perimeter is the leaf
• Convex hull the 3 or 2 largest contours (the blue line is the convex hull done)
• Use this convex hull to do a graph cut on the image and segmentate it

If you do those steps, you'll end up with images like these:

I won't post the code here, but you can check it out in my messy github. I hope you don't mind it was made in python.

Leaf - Github

Still, I have a couple of things to finish that could improve the result.. Roadmap would be:

• Define the mask in the graphcut (like its described in the doc)
• Apply region grow may give a better convex hull
• Remove all edges that touch the border of the image can help to identify larger edges

Well, again, I hope it helps