Thanks for your response!
I tried brightness=1, contrast=1, saturation=1, hue=0 in both the methods you suggested, which should theoretically return the original image (looking at the comments in the adjust_brightness function in source 15 and the functions below it) but both methods do not, while they do return the same image.
I am using the following to display the output image:
plt.imshow(img)
fig = plt.gcf()
fig.set_size_inches(14, 10)
plt.show()

Could there be an issue here? Or did I misunderstand something?