How to change the contrast and brightness of an image using OpenCV in Python?

In OpenCV, to change the contrast and brightness of an image we could use cv2.convertScaleAbs(). The syntax we use for this method is as follows −

cv2.convertScaleAbs(image, alpha, beta)

Where

• image is the original input image.

• alpha is the contrast value. To lower the contrast, use 0 < alpha < 1. And for higher contrast use alpha > 1.

• beta is the brightness value. A good range for brightness value is [-127, 127]

We could also apply the cv2.addWeighted() function to change the contrast and brightness of an image. We have discussed it in example 2.

Steps

To change the contrast and brightness of an image, you could follow the steps given below −

• Import the required library OpenCV. Make sure you have already installed it.

• Read the input image using cv2.imread() method. Specify the full path of the image.

• Define alpha (it controls contrast) and beta (it controls brightness) and call convertScaleAbs() function to change the contrast and brightness of the image. This function returns the image with adjusted contrast and brightness. Alternatively, we can also use the cv2.addWeighted() method to change contrast and brightness

• Display the contrast and brightness adjusted image.

Let's see the examples to change the contrast and brightness of an image.

Input Image

We will use the following image as the input file in the examples below.

Example

In this Python program, we change the contrast and brightness of the input image using cv2.convertScaleAbs() method.

# import the required library
import cv2

# read the input image
image = cv2.imread('food1.jpg')

# define the alpha and beta
alpha = 1.5 # Contrast control
beta = 10 # Brightness control

# call convertScaleAbs function
adjusted = cv2.convertScaleAbs(image, alpha=alpha, beta=beta)

# display the output image
cv2.imshow('adjusted', adjusted)
cv2.waitKey()
cv2.destroyAllWindows()

Output

When you execute the above code it will produce the following output window -

Example

In this Python program, we change the contrast and brightness of the input image using cv2.addWeighted() method.

# import required library
import cv2

# read the input image
img = cv2.imread('food1.jpg')

# define the contrast and brightness value
contrast = 5. # Contrast control ( 0 to 127)
brightness = 2. # Brightness control (0-100)

# call addWeighted function. use beta = 0 to effectively only
operate on one image
out = cv2.addWeighted( img, contrast, img, 0, brightness)

# display the image with changed contrast and brightness
cv2.imshow('adjusted', out)
cv2.waitKey(0)
cv2.destroyAllWindows()

Output

When you execute the above code, it will produce the following output window.