The API is the same on Node and on the browser:

const { mssim, ssim_map, performance } = ssim(imgBuffer1, imgBuffer2, options)

For CLI specific usage, check the dedicated page here.

ssim.js takes 2 paths to images and a 3rd optional parameter for additional options:

If you want use the options parameter you can call ssim.js with:

import ssim from 'ssim.js';

const out = ssim('./img1.jpg', './img2.jpg', { downsample: 'fast' })

The returned value is an object that contains the mean ssim value (mssim), the time needed to perform the computation (performance) and the ssim window matrix (ssim_map).

ssim_map matrix is of the form:

{
  data: Number[],
  width: Number,
  height: number
}

Where:

• width and height determine the dimensions of the matrix
• data holds the values at each position in row-major order

More succinctly:

import ssim from 'ssim.js';

try {
  const out = ssim('./img1.jpg', './img2.jpg')
  console.log(`SSIM: ${out.mssim} (${out.performance}ms)`)
} catch (err) {
  console.error('Error generating SSIM', err);
}

You can edit a similar node example here.

You can view a Node and Web SSIM comparison playground here.

You can pass a 3rd parameter containing a plain object and any of the following options:

• Setting k1 or k2 to 0 will use UQI (Universal Quality Index) since it's a subset of SSIM (when C1 or C2 are 0)
• When using canvas images will be retrieved as 8 bits/channel. You can use the bitDepth parameter to modify how SSIM computes the value but it will have no effect on how the image is read
• There are 3 downsample options:
  • false: disables downsizing
  • 'original': (default) implements the same downsizing than the original Matlab scripts
  • 'fast': relies on the canvas to do the downsizing (may lead to different results)
• There are 3 ssim options:
  • 'original': Uses a line-by-line port of the Matlab scripts and attempts to match them as closely as possible
  • 'fast': Uses a mathematically equivalent approach to 'original' but it's computationally faster.
  • 'bezkrovny': Uses a faster approach that similarly correlates with SSIM but doesn't match the original results exactly.
  • 'weber': (default) Is the fastest approach. Similar to Bezkrovny's, the results are close to but don't match the original SSIM results.