Image Processing to grayscale

import matplotlib.pyplot as plt
                                         
def to_grayscale(picture):
    image=np.array(Image.open(picture).convert("L"))     #L=lightness parameter
    plt.gray()                                           #plots the image in grayscale
    plt.imshow(image)                                    #R=0.2126, G=0.7152, B=0.0722?
    
def to_red(picture):
    image=np.array(Image.open(picture).convert("L"))  
    plt.imshow(image, cmap='Reds', alpha=0.5)      

def to_green(picture):    
    image=np.array(Image.open(picture).convert("L"))  
    plt.imshow(image, cmap='Greens', alpha=1) 
    
def to_blue(picture):
    image=np.array(Image.open(picture).convert("L"))  
    plt.imshow(image, cmap='Blues', alpha=0.5) 

picture=("painting.png")
   
to_grayscale(picture)
to_red(picture)
to_green(picture)
to_blue(picture)
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Output

https://github.com/JayaParmar/Data-Analysis-with-Python/blob/master/painting.PNG