HSV OpenCv colour range

Question

Can anyone please tell me a name of a website or any place from where I can get the upper and lower range of HSV of basic colours like

yellow,green,red,blue,black,white,orange

Actually I was making a bot which would at first follow black coloured line and then in the middle of the line there would be another colour given from where 3 different lines of different colour gets divided.The bot needs to decide which line to follow. For that I need the proper range of hsv colours

hue is here: de.m.wikipedia.org/wiki/HSV-Farbraum#/media/… in opencv, hue precision is halfed to fit in a byte, so hue channel is range 0..180 only. To not use whitish colors or blackish colors you should add thresholds for saturation and value channels. — Micka

warl0ck warl0ck · Accepted Answer · 2018-08-16T07:12:57

Inspired from the answer at answers.opencv link.

According to docs here

the HSV ranges like H from 0-179, S and V from 0-255, so as for your requirements for lower range and upper range example you can do for any given [h, s, v] to

[h-10, s-40, v-40] for lower

and

[h+10, s+10, v+40] for upper for the yellow,green,red,blue,black,white,orange rgb values.

Copied code from the example :

import cv2
import numpy as np

image_hsv = None   # global ;(
pixel = (20,60,80) # some stupid default

# mouse callback function
def pick_color(event,x,y,flags,param):
    if event == cv2.EVENT_LBUTTONDOWN:
        pixel = image_hsv[y,x]

        #you might want to adjust the ranges(+-10, etc):
        upper =  np.array([pixel[0] + 10, pixel[1] + 10, pixel[2] + 40])
        lower =  np.array([pixel[0] - 10, pixel[1] - 10, pixel[2] - 40])
        print(pixel, lower, upper)

        image_mask = cv2.inRange(image_hsv,lower,upper)
        cv2.imshow("mask",image_mask)

def main():
    import sys
    global image_hsv, pixel # so we can use it in mouse callback

    image_src = cv2.imread(sys.argv[1])  # pick.py my.png
    if image_src is None:
        print ("the image read is None............")
        return
    cv2.imshow("bgr",image_src)

    ## NEW ##
    cv2.namedWindow('hsv')
    cv2.setMouseCallback('hsv', pick_color)

    # now click into the hsv img , and look at values:
    image_hsv = cv2.cvtColor(image_src,cv2.COLOR_BGR2HSV)
    cv2.imshow("hsv",image_hsv)

    cv2.waitKey(0)
    cv2.destroyAllWindows()

if __name__=='__main__':
    main()

Above code is for when you want to directly select the HSV range from the image or video you are capturing, by clicking on the desired color.

If you want to predefine your ranges you can just use write simple code snippet using inbuilt python library colorsys to convert rbg to hsv using colorsys.rgb_to_hsv function

example in docs

Note this function accepts rgb values in range of 0 to 1 only and gives hsv values also in 0 to 1 range so to use the same values you will need to normalize it for opencv

code snippet

import colorsys
'''
convert given rgb to hsv opencv format
'''

def rgb_hsv_converter(rgb):
    (r,g,b) = rgb_normalizer(rgb)
    hsv = colorsys.rgb_to_hsv(r,g,b)
    (h,s,v) = hsv_normalizer(hsv)
    upper_band = [h+10, s+40, v+40]
    lower_band = [h-10, s-40, v-40]
    return {
        'upper_band': upper_band,
        'lower_band': lower_band
    }

def rgb_normalizer(rgb):
    (r,g,b) = rgb
    return (r/255, g/255, b/255)

def hsv_normalizer(hsv):
    (h,s,v) = hsv
    return (h*360, s*255, v*255)

rgb_hsv_converter((255, 165, 0))

will return

{'upper_band': [48.82352941176471, 295.0, 295.0], 'lower_band': [28.82352941176471, 215.0, 215.0]}

which is your orange hsv bands.

HSV OpenCv colour range

1 Answers