Example: Grayscale Morphology

Grayscale opening is a local minimum followed by a local maximum. It removes bright protrusions smaller than the structuring element while retaining the image geometry. Grayscale closing performs the dual maximum-then-minimum operation and fills small dark holes.

let opened = GrayscaleOpeningFilter::new(2)
    .apply_native(&sigmoid, &backend)?;
let closed = GrayscaleClosingFilter::new(2)
    .apply_native(&sigmoid, &backend)?;

The radius is measured in voxels, not physical units. Choose it from the feature size you intend to remove and account for anisotropic spacing before using the filter on a clinical volume. Both operations use replicate padding at the boundary, so their behavior differs from binary erosion’s background-outside policy.

Source and verification

Source: crates/ritk-filter/examples/book_processing_pipeline.rs

cargo run -p ritk-filter --example book_processing_pipeline -- \
  docs/book/figures/processing_pipeline.svg

The figure renders the opening stage on [0, 1]; the closing call above follows the same image contract and can be inspected with the same display helper. The opening result therefore shows local intensity removal directly. Tests cover radius zero identity, monotonicity, idempotence, safe-border behavior, and native/generic parity.