HSV color ranges for VIBGYOR colors

Question

I am developing an app which detects major colour in the frame. I used python code and HSV colour ranges to do this. My sample code for detecting blue is as below.

import cv2    
def detectBlue(frame):
        # Convert BGR to HSV
        hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)
        # define range of green color in HSV
        lower_blue = np.array([101, 39, 64])
        upper_blue = np.array([140, 255, 255])
        mask = cv2.inRange(hsv, lower_blue, upper_blue)
        kernel = np.ones((5,5),'int')
        dilated = cv2.dilate(mask,kernel)
        # Bitwise-AND mask and original image
        res = cv2.bitwise_and(frame,frame, mask=mask)
        ret,thrshed = cv2.threshold(cv2.cvtColor(res,cv2.COLOR_BGR2GRAY),3,255,cv2.THRESH_BINARY)
        #img,contours,hier = cv2.findContours(thrshed,cv2.RETR_LIST,cv2.CHAIN_APPROX_SIMPLE)
        contours,hier = cv2.findContours(thrshed,cv2.RETR_LIST,cv2.CHAIN_APPROX_SIMPLE)
        area = [0]
        for cnt in contours:
            #Contour area is taken
            area.append(cv2.contourArea(cnt))
        return max(area)

I created similar functions for Red and Green with HSV color ranges as below.

Green:
lower_green = [65,60,60])
upper_green = [80,255,255]

Red:
lower_red = [170,120,70] 
upper_red = [180,255,255]

Now I am trying to do the same for all VIBGYOR colors, but I am not getting proper color ranges for all these. I tried converting RGB code to HSV using this python code.

import colorsys

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((255,255,255))

But, these ranges did not work properly when tested. I searched a lot to find out best HSV ranges for all these colors, but no use. Can anybody suggest any approach to find best and more accurate color ranges for many colors.?

lenik lenik · Accepted Answer · 2020-01-07T07:17:45

You may take a pure red color, RGB( 255, 0, 0 ), convert it to HSV and the resulting hue (something around 0 -- zero) will be the center value for red. Do the same for the rest of the colors you want to define in HSV space. Green would be somewhere around 55, blue -- 120 and so on...

HSV color ranges for VIBGYOR colors

1 Answers