Histogram and Histogram Equalization of an image

Aim

To obtain a histogram for finding the frequency of pixels in an Image with pixel values ranging from 0 to 255. Also write the code using OpenCV to perform histogram equalization.

Software Required

Anaconda - Python 3.7

Algorithm

Step1:

Import cv2, matplotlib.py libraries and display the saved images using cv2.imshow().

Step2:

Use cv2.calcHist(images, channels, mask, histSize, ranges[, hist[, accumulate]]) to find the histogram of the image.

Step3:

Plot the image and its stem plots using the plt.show() and plt.stem() functions.

Step4:

Equalize the grayscale image using the in-built function cv2.equalizeHist().

Step5:

Print the original and equalized image using cv2.imshow() and end the program.

Program

# Developed By: Y SHAVEDHA
# Register Number: 212221230095

import cv2
import matplotlib.pyplot as plt

# Write your code to find the histogram of gray scale image and color image channels.
color_image=cv2.imread("rcolorimg2.jpg")
gray_image=cv2.imread("gimg.jpg")
cv2.imshow("Gray Image",gray_image)
cv2.imshow("Color_image",color_image)
cv2.waitKey(0)
cv2.destroyAllWindows()


# Display the histogram of gray scale image and any one channel histogram from color image
hist_g = cv2.calcHist([gray_image],[0],None,[256],[0,256])
plt.figure()
plt.imshow(gray_image)
plt.show()
plt.title("Histogram")
plt.xlabel("Grayscale Value")
plt.ylabel("Pixel Count")
plt.stem(hist_g)
plt.show()

hist_c = cv2.calcHist([color_image],[2],None,[256],[0,256])
plt.figure()
plt.imshow(color_image)
plt.show()
plt.title("Histogram of Color Image - Red Channel")
plt.xlabel("Intensity Value")
plt.ylabel("Pixel Count")
plt.stem(hist_c)
plt.show()


# Write the code to perform histogram equalization of the image. 
gray_image = cv2.imread("gimg.jpg",0)
cv2.imshow("Gray Image",gray_image)
equ = cv2.equalizeHist(gray_image)
cv2.imshow("Equalized Image",equ)
cv2.waitKey(0)
cv2.destroyAllWindows

Output

Input Grayscale Image and Color Image

Histogram of Grayscale Image and any channel of Color Image

GRAY SCALE IMAGE

RED CHANNEL OF COLOR IMAGE

Histogram Equalization of Grayscale Image

Result:

Thus the histogram for finding the frequency of pixels in an image with pixel values ranging from 0 to 255 is obtained. Also,histogram equalization is done for the gray scale image using OpenCV.

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