from PIL import Image

user_choice=input("Fichier à ouvrir ? ")

image_base=Image.open(user_choice)
image_base.show()
final_image=image_base.copy()

for i in range(image_base.size[0]):
    for j in range(image_base.size[1]):

        p=image_base.getpixel((i,j))

        final_image.putpixel((i,i-j),p)
final_image.show()
fichierfinal='Retouche'+user_choice
final_image.save(fichier_final)