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How to find the HSV values of a color using OpenCV Python?
To find the HSV values of a color, we can use color space conversion from BGR to HSV. First we define the color value in BGR format as numpy.ndarray and then convert it to HSV space.
We can also find the lower and upper limits of HSV value as [H-10, 100, 100] and [H+10, 255, 255] respectively. These lower and upper limits can be used to track an object of particular color.
To find the HSV values of a color, follow the steps given below −
Steps
Import the required libraries. In all the following Python examples, the required Python libraries are OpenCV and NumPy. Make sure you have already installed them.
import cv2 import numpy as np
Define a numpy.ndarray of dtype=np.uint8 for the color.
green = np.uint8([[[0, 255, 0]]])
Convert the above defined color to HSV.
hsvGreen = cv2.cvtColor(green, cv2.COLOR_BGR2HSV)
Print the color values.
print("HSV of Green:", hsvGreen)
Let's look at some program examples to understand it clearly.
Example 1
In this example, we find the HSV value for green color. The BGR value of green is [0,255,0].
# import required libraries import numpy as np import cv2 # define a numpy.ndarray for the color # here insert the bgr values which you want to convert to hsv green = np.uint8([[[0, 255, 0]]]) # convert the color to HSV hsvGreen = cv2.cvtColor(green, cv2.COLOR_BGR2HSV) # display the color values print("BGR of Green:", green) print("HSV of Green:", hsvGreen) # Compute the lower and upper limits lowerLimit = hsvGreen[0][0][0] - 10, 100, 100 upperLimit = hsvGreen[0][0][0] + 10, 255, 255 # display the lower and upper limits print("Lower Limit:",lowerLimit) print("Upper Limit", upperLimit)
Output
When you run the above Python program, it will produce the following output −
BGR of Green: [[[ 0 255 0]]] HSV of Green: [[[ 60 255 255]]] Lower Limit: (50, 100, 100) Upper Limit (70, 255, 255)
Example 2
In this example, we find the HSV value for a color whose BGR value is [106,76,89].
# import required libraries import numpy as np import cv2 green = np.uint8([[[0, 255, 0]]]) # convert the color to HSV hsvGreen = cv2.cvtColor(green, cv2.COLOR_BGR2HSV) # here insert the bgr values which you want to convert to hsv bgr = np.uint8([[[106,76,89]]]) hsv = cv2.cvtColor(green, cv2.COLOR_BGR2HSV) print("BGR Value:", bgr) print("HSV Value:", hsv) # compute the lower and upper limits lowerLimit = hsvGreen[0][0][0] - 10, 100, 100 upperLimit = hsvGreen[0][0][0] + 10, 255, 255 # display the lower and upper limits print("Lower Limit:",lowerLimit) print("Upper Limit", upperLimit)
Output
When you run the above python program, it will produce the following output −
BGR Value: [[[76 76 89]]] HSV Value: [[[ 60 255 255]]] Lower Limit: (50, 100, 100) Upper Limit (70, 255, 255)
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