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Simple tips to calculate the Structural Similarity Index (SSIM) between two images with Python

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Simple tips to calculate the Structural Similarity Index (SSIM) between two images with Python

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The Structural Similarity Index (SSIM) is really a perceptual metric that quantifies the image quality degradation that is due to processing such as for example information compression or by losings in information transmission. This metric is simply the full reference that needs 2 pictures through the exact exact same shot, this implies 2 graphically identical pictures to your eye. The 2nd image generally speaking is compressed or has another type of quality, that is the purpose of this index. SSIM is generally found in the video clip industry, but has aswell a strong application in photography. SIM actually steps the difference that is perceptual two comparable pictures. It cannot judge which of this two is much better: that must definitely be inferred from once you understand that will be the one that is original that has been subjected to extra processing such as for example compression or filters.

In this specific article, we will explain to you just how to calculate accurately this index between 2 images making use of Python.


To follow along with this guide you will need:

  • Python 3
  • PIP 3

That being said, why don\’t we begin !

1. Install Python dependencies

Before implementing the logic, you need to install some crucial tools that should be utilized by the logic. This tools are set up through PIP because of the after demand:

These tools are:

  • scikitimage: scikit-image is an accumulation algorithms for image processing.
  • opencv: OpenCV is just a library that is highly optimized give attention to real-time applications.
  • imutils: a number of convenience functions which will make basic image processing functions such as for example interpretation, rotation, resizing, skeletonization, showing Matplotlib pictures, sorting contours, detecting sides, and a lot more easier with OpenCV and both Python 2.7 and Python 3.

This tutorial will work with any platform where Python works (Ubuntu/Windows/Mac).

2. Write script

The logic to compare the pictures could be the after one. Making use of the compare_ssim way of the measure module of Skimage. This process computes the mean structural similarity index between two pictures. It gets as arguments:

X, Y: ndarray

Pictures of every dimensionality.

win_size: int or None

The side-length for the sliding screen used in comparison. Should be a value that is odd. If gaussian_weights does work, this is certainly ignored together with screen size shall rely on sigma.

gradientbool, optional

If real, additionally get back the gradient with regards to Y.

data_rangefloat, optional

The information number of the input image (distance between minimal and maximum feasible values). By default, this will be approximated through the image data-type.

multichannelbool, optional

If real, treat the final measurement of this array as stations. Similarity calculations are done separately for every single channel then averaged.

gaussian_weightsbool, optional

If real, each area has its mean and variance spatially weighted by way of A gaussian kernel that is normalized of sigma=1.5.

fullbool, optional

If real, additionally get back the entire similarity image that is structural.


The mean structural similarity over the image.


The gradient regarding the structural similarity index between X and Y [2]. This really is just returned if gradient is defined to real.


The complete SSIM image. This will be only came back if complete is defined to True.

As first, we are going to browse the pictures with CV from the supplied arguments and now we\’ll use a black colored and white filter (grayscale) so we\’ll apply the mentioned logic to those pictures. Produce the script that is following and paste the after logic on the file:

This script is founded on the rule posted by @mostafaGwely about this repository at Github. The rule follows exactly the logic that is same from the repository, nevertheless it eliminates an error of printing the Thresh of the pictures essay writer. The production of operating the script with all the pictures using the command that is following

Will create the following output (the demand within the picture makes use of the brief argument description -f as –first and -s as –second ):

The algorithm will namely print a string \»SSIM: $value\», you could change it out while you want. In the event that you compare 2 precise pictures, the worth of SSIM should really be clearly 1.0.

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