1. opencv realizes simple color recognition

Reference resources

1. Pysource Youtube Teaching video
2. BGR HSV Color model

step

One 、 BGR and HSV Color model

BGR Model
BGR The model represents three color channels ： red 、 green 、 blue , use BGR The color of the image of the model is weighted and mixed by red, green and blue .
The disadvantages of such models are obvious , It is difficult to express a color . For example, you modified the following BGR Medium B value , Indirectly , G and R The color of the channel will also be changed .

HSV Model
H Express Hue Color ;S Express Saturation saturation ;V Express Value Lightness .
The simple understanding is
H Specify a color , from 0 To 360;
S Is the extent of white light , from 0 To 1, 0 Indicates highest saturation , Is the most white light ;
V Express lightness , from 0 To 1, 0 The darkest

Two 、 Using the camera , utilize HSV Realize color recognition

1. Ideas
Read camera video stream , Take the middle of the window , Change its pixel value (BGR) Convert to HSV, And then according to Hue To simply judge the color . Then it will be displayed on the window .

2. Code

import cv2

cap = cv2.VideoCapture(0)
cap.set(cv2.CAP_PROP_FRAME_WIDTH,1080) #set window's width and height
cap.set(cv2.CAP_PROP_FRAME_HEIGHT,780) 

while True:
    _, frame = cap.read()
    hsv_frame = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)
    height,width,_ = hsv_frame.shape

    wx = int(width/2) # center 
    wy = int(height/2)

    center_color = hsv_frame[wy,wx] # Center point HSV Pixel values 
    hue_value = center_color[0] # take Hue

    if hue_value < 5:
        color = 'RED'
    elif hue_value < 22:
        color = 'ORANGE'
    elif hue_value < 33:
        color = 'YELLOW'
    elif hue_value < 78:
        color = 'GREEN'
    elif hue_value <131:
        color = 'BLUE'
    elif hue_value < 167:
        color = 'VIOLET'
    else:
        color ='RED'
        
    bgr_color = frame[wy,wx]
    b,g,r = int(bgr_color[0]),int(bgr_color[1]),int(bgr_color[2])

    cv2.circle(frame,(wx,wy),5,(0,255,0),3) # center (x,y)
    cv2.putText(frame,color,(10,50),0,1,(b,g,r),2)
    cv2.imshow('frame',frame)
    key = cv2.waitKey(1)
    if key ==27:
        break

cap.release()
cv2.destroyAllWindows()

3. effect