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Changelog

Source: NEWS.md

thinr 0.3.0.9000 (development version)

  • Development version bump following the 0.3.0 CRAN release.

  • Internal, with no change to any output: the unused thinr::is_border_4() helper was removed from src/thinr_common.h. Its last callers were the stentiford and pavlidis kernels, dropped 2026-05-20; nothing has referenced it since. The header now declares only the two helpers that are actually used.

  • Internal, with no change to any output: the Zhang-Suen crossing number A(p) and neighbour count B(p) were re-implemented inline in src/zhang_suen.cpp, src/lee.cpp, and src/holt.cpp instead of calling the shared thinr::crossing_number() / thinr::neighbour_count() in src/thinr_common.h, which only src/hilditch.cpp used. A future correctness fix to the shared definition would have reached one of the four kernels that need it and silently missed the other three. All four now call the shared helpers. The replacement expressions are token-identical to the inline copies they replace; identical output was verified empirically across 257 binary images (degenerate, boundary, synthetic, and real chart masks) for all seven methods (#F018).

thinr 0.3.0

CRAN release: 2026-07-26

Correctness fixes from the figureextract ecosystem review (2026-07-03). All are boundary conditions the published algorithms assume away; see the new vignette("correctness-properties") for the guarantees they restore.

  • thin() now skeletonises shapes that touch the matrix border correctly. The kernels inspect an 8-neighbourhood and so never deleted pixels in the outermost row or column, leaving edge-touching shapes two to three pixels thick; thin() now pads the image with a one-pixel background margin and crops it back, so a shape thins identically whether or not it touches the frame. Applies to all seven methods (#F012).

  • thin(method = "opta") now keeps two-pixel-wide strokes connected. The SPTA kernel evaluated all four contour directions against the pre-cycle snapshot and deleted them in one batch, so both sides of a 2px stroke were removed together and the skeleton fragmented (a 2×9 bar collapsed to its four corner pixels). Deletion is now sequential per direction, as Naccache & Shinghal’s two-scan formulation requires (#F011).

  • distance_transform(metric = "manhattan" | "chessboard") now returns Inf for a fully-foreground image (no background pixel exists), matching the "euclidean" metric and EBImage::distmap(). The two-pass metrics previously seeded foreground with a finite sentinel that leaked out as a plausible-looking but meaningless finite distance (#F015).

  • thin(), distance_transform(), and medial_axis() now reject NA input with a clear error at the coercion boundary instead of silently turning it into NA_integer_ (INT_MIN) in the C++ kernels (#F016).

  • thin(method = "hilditch") now thins junctions to the published parallel form. The look-ahead conditions 3 and 4 skip deleting a pixel only when a cardinal neighbour has crossing number A == 1 on the current image; the kernel had compared the look-ahead crossing number (computed with the centre already removed) against 1, which is strictly stronger and also spared junction neighbours where A >= 2, leaving a redundant pixel beside the junction. Skeletons are now equal to or thinner than before, never thicker (verified against a reference implementation of the published form over random images) (#F014).

  • Added a connectivity-preservation property test across all seven methods and tightened the Holt straight-line test (#F013).

  • Documented and pinned the isolated-2×2-block behaviour: the default zhang_suen erases an isolated 2×2 block entirely while guo_hall keeps one pixel. See vignette("choosing-a-method") for guidance on small-blob masks (#F017).

  • Removed thinImage(). Use thin() (Zhang-Suen is the default method).

thinr 0.2.0

CRAN release: 2026-05-27

Initial CRAN release.