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androidopencvcolorsrgbahsv

OpenCV Android Green Color Detection

currently I'm making an app where user will detect green colors. I use this photo for testing: enter image description here

My problem is that I can not detect any green pixel. Before I worked with blue color and everything worked fine. Now I can't detect anything though I tried different combinations of RGB. I wanted to know whether it's problem with green or my detection range, so I made an image in paint using (0, 255, 0) and it worked. Why it can't see this circle then? I use this code for detection:

Core.inRange(hsv_image, new Scalar([I change this value]), new Scalar(60, 255, 255), ultimate_blue);

It could have been that I set wrong Range, but I use Photoshop to get color of one of green pixels and convert RGB value of it into HSV. Yet it doesn't work. It don't detect even pixel that I've sampled. What's wrong? Thanks in advance.

Using Miki's answer:

enter image description here

Solution

  • Green color is HSV space has H = 120 and it's in range [0, 360].

    OpenCV halves the H values to fit the range [0,255], so H value instead of being in range [0, 360], is in range [0, 180]. S and V are still in range [0, 255].

    As a consequence, the value of H for green is 60 = 120 / 2.

    You upper and lower bound should be:

    // sensitivity is a int, typically set to 15 - 20 
[60 - sensitivity, 100, 100]
[60 + sensitivity, 255, 255]

    UPDATE

    Since your image is quite dark, you need to use a lower bound for V. With these values:

    sensitivity = 15;
[60 - sensitivity, 100, 50]  // lower bound
[60 + sensitivity, 255, 255] // upper bound

    the resulting mask would be like:

    enter image description here

    You can refer to this answer for the details.