HSV trackbar Opencv Python
A basic yet very useful application of OpenCV is to track color.
One major challenge while doing color detection is to include all the shades of color.
To solve this problem of shades instead of using RGB color space we use HSV color space.
Don’t know “How to create trackbar in OpenCV Python’ Read ->”Trackbars in OpenCV python“
HSV trackbar code
#import opencv and numpy
import cv2
import numpy as np
#trackbar callback fucntion to update HSV value
def callback(x):
global H_low,H_high,S_low,S_high,V_low,V_high
#assign trackbar position value to H,S,V High and low variable
H_low = cv2.getTrackbarPos('low H','controls')
H_high = cv2.getTrackbarPos('high H','controls')
S_low = cv2.getTrackbarPos('low S','controls')
S_high = cv2.getTrackbarPos('high S','controls')
V_low = cv2.getTrackbarPos('low V','controls')
V_high = cv2.getTrackbarPos('high V','controls')
#create a seperate window named 'controls' for trackbar
cv2.namedWindow('controls',2)
cv2.resizeWindow("controls", 550,10);
#global variable
H_low = 0
H_high = 179
S_low= 0
S_high = 255
V_low= 0
V_high = 255
#create trackbars for high,low H,S,V
cv2.createTrackbar('low H','controls',0,179,callback)
cv2.createTrackbar('high H','controls',179,179,callback)
cv2.createTrackbar('low S','controls',0,255,callback)
cv2.createTrackbar('high S','controls',255,255,callback)
cv2.createTrackbar('low V','controls',0,255,callback)
cv2.createTrackbar('high V','controls',255,255,callback)
while(1):
#read source image
img=cv2.imread("ballimage.jpg")
#convert sourece image to HSC color mode
hsv = cv2.cvtColor(img, cv2.COLOR_BGR2HSV)
#
hsv_low = np.array([H_low, S_low, V_low], np.uint8)
hsv_high = np.array([H_high, S_high, V_high], np.uint8)
#making mask for hsv range
mask = cv2.inRange(hsv, hsv_low, hsv_high)
print (mask)
#masking HSV value selected color becomes black
res = cv2.bitwise_and(img, img, mask=mask)
#show image
cv2.imshow('mask',mask)
cv2.imshow('res',res)
#waitfor the user to press escape and break the while loop
k = cv2.waitKey(1) & 0xFF
if k == 27:
break
#destroys all window
cv2.destroyAllWindows()Read this great article on Colorspaces and know why convert RGB to HSV for color detection.
Read More about Anatomy of a digital Image
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