ppu-ocv/deskew.js

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

export class DeskewService{verbose;minimumAreaThreshold;constructor(options={}){this.verbose=options.verbose??false;this.minimumAreaThreshold=options.minimumAreaThreshold??20}log(message){if(this.verbose){console.log(`[DeskewService] ${message}`)}}async calculateSkewAngle(canvas){let processor=new ImageProcessor(canvas);let mat=processor.grayscale().threshold({lower:0,upper:255,type:cv.THRESH_BINARY+cv.THRESH_OTSU}).toMat();let contours=new Contours(mat,{mode:cv.RETR_LIST,method:cv.CHAIN_APPROX_SIMPLE});processor.destroy();let minAngle=-20;let maxAngle=20;let minArea=this.minimumAreaThreshold;let textRegions=[];contours.iterate((contour)=>{let rect=contours.getRect(contour);let area=rect.width*rect.height;if(area<minArea)return;let aspectRatio=rect.width/rect.height;if(aspectRatio>0.2&&aspectRatio<10){textRegions.push({rect,contour,area,aspectRatio})}});if(textRegions.length===0){this.log("No valid text regions found for skew calculation.");contours.destroy();return 0}let averageHeight=textRegions.reduce((sum,region)=>sum+region.rect.height,0)/textRegions.length;let filteredRegions=textRegions.filter((region)=>{return region.rect.height<=averageHeight*1.5});this.log(`Found ${filteredRegions.length} text regions for skew analysis.`);let minRectAngles=calculateMinRectAngles(filteredRegions);let baselineAngles=calculateBaselineAngles(filteredRegions);let houghAngles=calculateHoughAngles(mat,minAngle,maxAngle,(m)=>this.log(m));contours.destroy();let allAngles=[...minRectAngles.map((a)=>({...a,method:"minRect"})),...baselineAngles.map((a)=>({...a,method:"baseline"})),...houghAngles.map((a)=>({...a,method:"hough"}))];if(allAngles.length===0){this.log("No angles detected from any method.");return 0}let consensusAngle=calculateConsensusAngle(allAngles,minAngle,maxAngle,(m)=>this.log(m));this.log(`Calculated skew angle: ${consensusAngle.toFixed(3)}° (from ${allAngles.length} measurements)`);return consensusAngle}async deskewImage(canvas){this.log("Starting image deskewing process");let angle=await this.calculateSkewAngle(canvas);this.log(`Detected skew angle: ${angle.toFixed(2)}°. Rotating image by ${-angle.toFixed(2)}°...`);let processor=new ImageProcessor(canvas);try{let rotatedCanvas=processor.rotate({angle}).toCanvas();return rotatedCanvas}finally{processor.destroy()}}}import{Contours}from"./contours.js";import{cv}from"./cv-provider.js";import{calculateBaselineAngles,calculateConsensusAngle,calculateHoughAngles,calculateMinRectAngles}from"./deskew-angles.js";import{ImageProcessor}from"./image-processor.js";