Chessboard Detection Example

Reference: crates/calib-targets/examples/detect_chessboard.rs — end-to-end image-in / detection-out using the facade’s default chessboard configuration.

Example output overlay for chessboard detection on testdata/mid.png.

Quick run

cargo run --release -p calib-targets --example detect_chessboard -- testdata/mid.png

The example:

1. Decodes the image with image::open(...).to_luma8().
2. Calls calib_targets::detect::detect_chessboard(&img, &DetectorParams::default()).
3. Prints the detected Detection — labelled corner count, cell size, the two grid-direction angles, and every (i, j) → pixel_position pair.

If detection fails (None), rerun with the _best helper, which tries three pre-tuned configs (default + tighter + looser) and returns whichever produced the most labelled corners:

cargo run --release -p calib-targets --example detect_chessboard_best -- testdata/mid.png

Instrumentation

The chessboard crate’s diagnostic entry point is calib_targets_chessboard::trace_topological(corners, params), which returns a serializable TopologicalTrace layered over the production detect_grid_all path (so the trace matches what detect() actually does). It records every input corner with its usable flag, the labelled connected components ((u, v) -> source_index), and summary counters; the final-check drop accounting lives in the pipeline’s GeometryCheckTrace. See The Chessboard Detector §7 for the field-by-field walkthrough.

The crates/calib-targets-py/examples/overlay_chessboard.py script draws labelled corners in gold with their (i, j) text, grid edges, cluster-direction tangent lines, and the faint grey input-corner cloud as context.

Direct crate-level usage

If you need control over the ChESS corner front-end (e.g., custom ChessConfig), bypass the facade:

#![allow(unused)]
fn main() {
use calib_targets::detect::{default_chess_config, detect_corners};
use calib_targets_chessboard::{Detector, DetectorParams};
use image::ImageReader;

let img = ImageReader::open("board.png").unwrap().decode().unwrap().to_luma8();
let chess_cfg = default_chess_config();
let corners = detect_corners(&img, &chess_cfg);

let params = DetectorParams::default();
let detector = Detector::new(params);

if let Some(detection) = detector.detect(&corners) {
    println!("{} labelled corners", detection.corners.len());
}
}

Detector::detect_all(&corners) returns every same-board component found in the scene (see the chessboard chapter for the multi-component contract).