image-js/lib/maskAnalysis/getContourPavlidis.js

Image processing and manipulation in JavaScript

import { getBitSafe, getCoordsFromIndex, } from "./utils/getExternalContourUtils.js";
const DR = [-1, 0, 1, 0];
const DC = [0, 1, 0, -1];
function turnLeft(d) {
    return ((d + 3) % 4);
}
function turnRight(d) {
    return ((d + 1) % 4);
}
/**
 * Return an array with the coordinates of the pixels that are on the
 * external border of the mask using Theo Pavlidis's tracing algorithm.
 * The reference is the top-left corner of the ROI.
 * @param mask - Mask to process.
 * @returns The array of external border pixels.
 */
export function getContourPavlidis(mask) {
    let index = 0;
    while (index < mask.size && mask.getBitByIndex(index) !== 1) {
        index++;
    }
    if (index === mask.size)
        return [];
    const [row, col] = getCoordsFromIndex(index, mask.width);
    return traceFrom(mask, col, row);
}
/**
 * Traces contour using Pavlidis algorithm.
 * @param mask - Mask in check.
 * @param startCol - Starting column.
 * @param startRow - Starting row.
 * @returns Array of contour points.
 */
function traceFrom(mask, startCol, startRow) {
    let row = startRow;
    let column = startCol;
    let dir = 2;
    let inPlaceTurns = 0;
    const seen = new Uint8Array(mask.width * mask.height);
    const contour = [];
    let visits = 0;
    while (true) {
        const idx = row * mask.width + column;
        if (!seen[idx]) {
            seen[idx] = 1;
            contour.push({ row, column });
        }
        else if (row === startRow && column === startCol) {
            if (visits === 2) {
                break;
            }
            else {
                visits++;
            }
        }
        const left = turnLeft(dir);
        const right = turnRight(dir);
        const c1r = row + DR[left];
        const c1c = column + DC[left];
        const c2r = row + DR[dir];
        const c2c = column + DC[dir];
        const c3r = row + DR[right];
        const c3c = column + DC[right];
        if (getBitSafe(mask, c1c, c1r) === 1) {
            dir = left;
            row = c1r;
            column = c1c;
            inPlaceTurns = 0;
        }
        else if (getBitSafe(mask, c2c, c2r) === 1) {
            row = c2r;
            column = c2c;
            inPlaceTurns = 0;
        }
        else if (getBitSafe(mask, c3c, c3r) === 1) {
            dir = right;
            row = c3r;
            column = c3c;
            inPlaceTurns = 0;
        }
        else {
            dir = right;
            inPlaceTurns++;
            if (inPlaceTurns >= 4)
                break;
        }
    }
    return contour;
}
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