How to detect blue color object using opencv

Question

i'm using that guide to detect blobs of a certain color. On that guide, it check for orange's blob and it use this values:

int orange[3] = {200, 250, 10};

On the guide it says that this values represents the orange in HSV.

I don't know how they calculate this values but i try to check for blue value converting from rgb to hsv but it doesn't work. What i have to detect is this color:

Any ideas on how to determinate HSV values to detect colors? thanks!!

Answer 1

For blue, it can be used as HSV values : [120,255,255]

I calculated it from GIMP, an open-source image processing tool like Photoshop. Similarly you can use any tools to do so.

But remember in OpenCV, Hue ranges from 0-180, S = 0-255, V = 0-255

But in GIMP, it is H = 0-360, S = 0-100, V = 0-100. So you have to apply scaling according to that.

A lot of interactive sites are available on googling. You can try that.

• To know how they convert these values, check its wikipedia page.
• Or you can check out the OpenCV docs to see how it works in OpenCV : cvtColor()

I just pasted the relation for you here: