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:

this color

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

Abid Rahman K · Accepted Answer · 2012-07-12 10:11:57Z

3

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:

enter image description here

edited Jul 12, 2012 at 10:11

answered Jul 12, 2012 at 10:00

Abid Rahman K

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8 Comments

Jayyrus Over a year ago

thanks for your reply, but if you see on the guide i highlight, color check is made in function of color variance and it use value for hue greater than 180...

Abid Rahman K Over a year ago

please post the link where it says the values in your question is orange.

Abid Rahman K Over a year ago

OK got it. I don't understand why they given so. But for you to check, just convert a RGB image to HSV and check out the maximum value in H plane.

Abid Rahman K Over a year ago

If V = 10, then the color is almost near to black.

Abid Rahman K Over a year ago

do u know rgb values of orange?

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