This tool computes (dis)similarity between two (or more) PNG images using algorithm approximating human vision.
Comparison is done using the SSIM algorithm (based on Rabah Mehdi's implementation) at multiple weighed resolutions.
The value returned is 1/SSIM-1, where 0 means identical image, and >0 (unbounded) is amount of difference. Values are not directly comparable with other tools.
- Comparison is done in in L*a*b* color space (D65 white point, gamma 2.2) with chroma subsampling. Other implementations use uncorrected sRGB or grayscale.
- Supports alpha channel.
- Only needs C (C99) and
libpngor Cocoa on OS X. No OpenCV or MATLAB needed.
dssim file-original.png file-modified.png
Will output something like "0.02341" (smaller is better) followed by a filename.
You can supply multiple filenames to compare them all with the first file:
dssim file.png modified1.png modified2.png modified3.png
You can save an image visualising the difference between the files:
dssim -o difference.png file.png file-modified.png
The dssim.c file is also usable as a C library.
You need libpng, zlib, pkg-config and make
make
Will give you dssim. On OS X make USE_COCOA=1 will compile without libpng.
You'll find downloads on GitHub releases page.
Scores for version 0.9 measured against TID2008 database:
| TID2008 Category | Spearman correlation |
|---|---|
| Noise | -0.866 |
| Noise2 | -0.882 |
| Safe | -0.884 |
| Hard | -0.903 |
| Simple | -0.920 |
| Exotic | -0.441 |
| Exotic2 | -0.619 |
| Full | -0.804 |