ssim — IMGMETRICS fidelity op

• Data kinds: image2d × image2d → scalar

• Call: import fullseye as fs; fs.ledger.ssim(a, b, data_range=None, win_size=11, sigma=1.5, K1=0.01, K2=0.03, channel_axis=None, crop_border=True) (to call the implementation directly, import imgmetrics; imgmetrics.ssim(a, b, data_range=None, win_size=11, sigma=1.5, K1=0.01, K2=0.03, channel_axis=None, crop_border=True); from the registry, opsimgmetrics.get("ssim"))

Usage

Structural similarity (Wang, Bovik, Sheikh & Simoncelli, IEEE TIP 13(4), 2004).

The defaults are the original paper's settings -- 11x11 Gaussian window σ=1.5, K1=0.01, K2=0.03, weighted population variance (no n/(n-1) correction to sample variance).

crop_border=True (default) drops a border as wide as the window radius from the mean. At the border, mirror-padded pixels mix into the statistics. Whether you drop it changes the value, so when comparing with numbers from elsewhere, always match this setting (the smaller the picture, the bigger the difference).

Returns

float

1.0 is a perfect match.

Detailed usage guide

• image_difference_metrics family guide

References (sample data, literature)

• Sample-data catalog (download URLs / licences) — 2-D uses skimage.data (BSD/public domain) plus synthetic images; 3-D lists download URLs for real data sources (Stanford, PDS, …).

• Operator provenance and references — the sources of the research/methods this op family came from.

• The canonical algorithm (author, year) and its uses are named in the family usage guide above.

Runnable examples (verified samples that actually call this op)

• image_quality_metrics — py -3.11 examples/image_quality_metrics.py

• poc_camera_shake_deblur — py -3.11 examples/poc_camera_shake_deblur.py

• poc_ct_fidelity — py -3.11 examples/poc_ct_fidelity.py

• poc_dehazing — py -3.11 examples/poc_dehazing.py

• poc_iqa_tid2013 — py -3.11 examples/poc_iqa_tid2013.py

• poc_superresolution_limits — py -3.11 examples/poc_superresolution_limits.py

Ops the type connects to (they accept scalar as input)

luma_limited_u8 · rank_data · tid2013_index

Same category (fidelity)

mse · rmse · psnr · ms_ssim · ssim_map

*Provenance: imgmetrics.py — IMGMETRICS operator registry. This per-op note is generated by tools/opdocs.py md (do not hand-edit).*

© 2026 Kazufumi Furuse — Fullseye operator documentation. Licensed under Apache-2.0.