ppu-ocv/contours.js

A type-safe, modular, chainable image processing library built on top of OpenCV.js with a fluent API leveraging pipeline processing.

export class Contours{contours;constructor(img,options={}){let opts={...defaultOptions(),...options};if(img instanceof cv.Mat){let contours=new cv.MatVector;let hierarchy=new cv.Mat;try{cv.findContours(img,contours,hierarchy,opts.mode,opts.method)}catch(error){throw error}hierarchy.delete();this.contours=contours}else{throw new Error("Invalid img type. Must be cv.Mat.")}}getAll(){return this.contours}getFromIndex(index){if(index<this.contours.size()){return this.contours.get(index)}return new cv.Mat}getRect(contour){return cv.boundingRect(contour)}iterate(callback){for(let i=0,len=this.contours.size();i<len;i++){let contour=this.contours.get(i);callback(contour)}return this}getLargestContourArea(){let maxArea=0;let largestContour=null;this.iterate((contour)=>{let area=cv.contourArea(contour);if(area>maxArea){maxArea=area;largestContour=contour}});return largestContour}getCornerPoints(options){const{canvas,contour=this.getLargestContourArea()}=options;let bbox={x0:0,y0:0,x1:canvas.width,y1:canvas.height};if(!contour){return{points:{topLeft:{x:bbox.x0,y:bbox.y0},topRight:{x:bbox.x1,y:bbox.y0},bottomLeft:{x:bbox.x0,y:bbox.y1},bottomRight:{x:bbox.x1,y:bbox.y1}},bbox}}let rect=cv.minAreaRect(contour);let vertices=cv.RotatedRect.points(rect);let points={topLeft:{x:0,y:0},topRight:{x:0,y:0},bottomRight:{x:0,y:0},bottomLeft:{x:0,y:0}};let sums=vertices.map((pt)=>pt.x+pt.y);let diffs=vertices.map((pt)=>pt.y-pt.x);let topLeftIdx=sums.indexOf(Math.min(...sums));let topRightIdx=diffs.indexOf(Math.min(...diffs));let bottomRightIdx=sums.indexOf(Math.max(...sums));let bottomLeftIdx=diffs.indexOf(Math.max(...diffs));if(!vertices[topLeftIdx]||!vertices[topRightIdx]||!vertices[bottomRightIdx]||!vertices[bottomLeftIdx]){return{points:{topLeft:{x:bbox.x0,y:bbox.y0},topRight:{x:bbox.x1,y:bbox.y0},bottomLeft:{x:bbox.x0,y:bbox.y1},bottomRight:{x:bbox.x1,y:bbox.y1}},bbox}}points.topLeft={x:vertices[topLeftIdx].x,y:vertices[topLeftIdx].y};points.topRight={x:vertices[topRightIdx].x,y:vertices[topRightIdx].y};points.bottomRight={x:vertices[bottomRightIdx].x,y:vertices[bottomRightIdx].y};points.bottomLeft={x:vertices[bottomLeftIdx].x,y:vertices[bottomLeftIdx].y};contour.delete();let ensureInBounds=(p)=>{p.x=Math.max(0,Math.min(canvas.width,p.x));p.y=Math.max(0,Math.min(canvas.height,p.y));return p};points.topLeft=ensureInBounds(points.topLeft);points.topRight=ensureInBounds(points.topRight);points.bottomLeft=ensureInBounds(points.bottomLeft);points.bottomRight=ensureInBounds(points.bottomRight);return{points,bbox}}getApproximateRectangleContour(options){const{threshold=0.02,contour=this.getLargestContourArea()}=options??{};if(!contour)return;let epsilon=threshold*cv.arcLength(contour,true);let approxContour=new cv.Mat;cv.approxPolyDP(contour,approxContour,epsilon,true);contour.delete();return approxContour}destroy(){try{this.contours.delete()}catch(error){}}}import{cv}from"./index";function defaultOptions(){return{mode:cv.RETR_EXTERNAL,method:cv.CHAIN_APPROX_SIMPLE}}