Having extracted the blood vessels, how to brighten them?

Question

I've used Kirsch filter to try and obtain the blood vessels, but the result isn't the best, as shown below:

Although the vessels have been obtained, they aren't bright enough. How do I go about making them 'more visible'?

Answer 1

I worked on retina vessel detection for a bit few years ago, and there are different ways to do it:

• If you don't need a top result but something fast, you can use oriented openings, see here and here .
• Then you have an other version using mathematical morphology version here .

For better results, here are some ideas:

• Personally, I used combination of Gabor filters, and results where pretty good. See the segmentation result here on the first image of drive .
• And Gabor can be combined with learning for a good result , or here .
• Few years ago, they claimed to have the best algorithm , but I've never had the opportunity to test it. I was sceptic about the performance gap and the way they thresholded the line detector results, it was kind of obscure.
• But I know that nowadays, many people try to tackle the problem using CNN, but I've not heard about significant improvements.

[EDIT] To answer your specific question, you can erase the bright ring, and then apply a histogram stretching. But I think that the methods I introduced before will work better than the filter you are using.

Answer 2

looks like, the solution for your problem is histogram equalization (we had the same problem for homework)

http://docs.opencv.org/3.1.0/d5/daf/tutorial_py_histogram_equalization.html#gsc.tab=0