image-compare

Simple image comparison in rust based on the image crate

Note that this crate is heavily work in progress. Algorithms are neither cross-checked not particularly fast yet. Everything is implemented in plain CPU with rayon multithreading. SIMD is under investigation on a feature branch (simd-experimental).

Supported now:

• Comparing grayscale and rgb images by structure
  • By RMS - score is calculated by:
  • By MSSIM
    • SSIM is implemented as described on wikipedia:
    • MSSIM is calculated by using 8x8 pixel windows for SSIM and averaging over the results
  • RGB type images are split to R,G and B channels and processed separately.
    • The worst of the color results is propagated as score but a float-typed RGB image provides access to all values.
    • As you can see in the gherkin tests this result is not worth it currently, as it takes a lot more time
    • It could be improved, by not just propagating the individual color-score results but using the worst for each pixel
    • This approach is implemented in hybrid-mode, see below
  • "hybrid comparison"
    • Splitting the image to YUV colorspace according to T.871
    • Processing the Y channel with MSSIM
    • Comparing U and V channels via RMS
    • Recombining the differences to a nice visualization image
    • Score is calculated as:
    • This allows for a good separation of color differences and structure differences
• Comparing grayscale images by histogram
  • Several distance metrics implemented see OpenCV docs:
    • Correlation
    • Chi-Square
    • Intersection
    • Hellinger distance