# What preprocessing steps to be followed before image comparison?

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For example I am trying to find the similarity between two images using skimage - SSIM. The code block will be as follows

from skimage.measure import compare_ssim as ssim
from skimage import io
from skimage.transform import resize

a = resize(a,b.shape)
ssim(a, b,multichannel=True)


I got the similarity score as follows

0.21009350738786017


Although both the images are same where one images in slightly oriented , I am getting very really low scores for this comparisons. Am I missing any preprocessing steps here before I compute compare images. If so what are the things I should consider before comparing images.

Thanks In Advance !!