getuserbarcode/src/decoder/bresenham.js

An advanced barcode-scanner written in JavaScript

import ImageWrapper from '../common/image_wrapper';

var Bresenham = {};

var Slope = {
    DIR: {
        UP: 1,
        DOWN: -1
    }
};
/**
 * Scans a line of the given image from point p1 to p2 and returns a result object containing
 * gray-scale values (0-255) of the underlying pixels in addition to the min
 * and max values.
 * @param {Object} imageWrapper
 * @param {Object} p1 The start point {x,y}
 * @param {Object} p2 The end point {x,y}
 * @returns {line, min, max}
 */
Bresenham.getBarcodeLine = function(imageWrapper, p1, p2) {
    var x0 = p1.x | 0,
        y0 = p1.y | 0,
        x1 = p2.x | 0,
        y1 = p2.y | 0,
        steep = Math.abs(y1 - y0) > Math.abs(x1 - x0),
        deltax,
        deltay,
        error,
        ystep,
        y,
        tmp,
        x,
        line = [],
        imageData = imageWrapper.data,
        width = imageWrapper.size.x,
        sum = 0,
        val,
        min = 255,
        max = 0;

    function read(a, b) {
        val = imageData[b * width + a];
        sum += val;
        min = val < min ? val : min;
        max = val > max ? val : max;
        line.push(val);
    }

    if (steep) {
        tmp = x0;
        x0 = y0;
        y0 = tmp;

        tmp = x1;
        x1 = y1;
        y1 = tmp;
    }
    if (x0 > x1) {
        tmp = x0;
        x0 = x1;
        x1 = tmp;

        tmp = y0;
        y0 = y1;
        y1 = tmp;
    }
    deltax = x1 - x0;
    deltay = Math.abs(y1 - y0);
    error = (deltax / 2) | 0;
    y = y0;
    ystep = y0 < y1 ? 1 : -1;
    for ( x = x0; x < x1; x++) {
        if (steep){
            read(y, x);
        } else {
            read(x, y);
        }
        error = error - deltay;
        if (error < 0) {
            y = y + ystep;
            error = error + deltax;
        }
    }

    return {
        line: line,
        min: min,
        max: max
    };
};

/**
 * Converts the result from getBarcodeLine into a binary representation
 * also considering the frequency and slope of the signal for more robust results
 * @param {Object} result {line, min, max}
 */
Bresenham.toBinaryLine = function(result) {
    var min = result.min,
        max = result.max,
        line = result.line,
        slope,
        slope2,
        center = min + (max - min) / 2,
        extrema = [],
        currentDir,
        dir,
        threshold = (max - min) / 12,
        rThreshold = -threshold,
        i,
        j;

    // 1. find extrema
    currentDir = line[0] > center ? Slope.DIR.UP : Slope.DIR.DOWN;
    extrema.push({
        pos: 0,
        val: line[0]
    });
    for ( i = 0; i < line.length - 2; i++) {
        slope = (line[i + 1] - line[i]);
        slope2 = (line[i + 2] - line[i + 1]);
        if ((slope + slope2) < rThreshold && line[i + 1] < (center * 1.5)) {
            dir = Slope.DIR.DOWN;
        } else if ((slope + slope2) > threshold && line[i + 1] > (center * 0.5)) {
            dir = Slope.DIR.UP;
        } else {
            dir = currentDir;
        }

        if (currentDir !== dir) {
            extrema.push({
                pos: i,
                val: line[i]
            });
            currentDir = dir;
        }
    }
    extrema.push({
        pos: line.length,
        val: line[line.length - 1]
    });

    for ( j = extrema[0].pos; j < extrema[1].pos; j++) {
        line[j] = line[j] > center ? 0 : 1;
    }

    // iterate over extrema and convert to binary based on avg between minmax
    for ( i = 1; i < extrema.length - 1; i++) {
        if (extrema[i + 1].val > extrema[i].val) {
            threshold = (extrema[i].val + ((extrema[i + 1].val - extrema[i].val) / 3) * 2) | 0;
        } else {
            threshold = (extrema[i + 1].val + ((extrema[i].val - extrema[i + 1].val) / 3)) | 0;
        }

        for ( j = extrema[i].pos; j < extrema[i + 1].pos; j++) {
            line[j] = line[j] > threshold ? 0 : 1;
        }
    }

    return {
        line: line,
        threshold: threshold
    };
};

/**
 * Used for development only
 */
Bresenham.debug = {
    printFrequency: function(line, canvas) {
        var i,
            ctx = canvas.getContext("2d");
        canvas.width = line.length;
        canvas.height = 256;

        ctx.beginPath();
        ctx.strokeStyle = "blue";
        for ( i = 0; i < line.length; i++) {
            ctx.moveTo(i, 255);
            ctx.lineTo(i, 255 - line[i]);
        }
        ctx.stroke();
        ctx.closePath();
    },

    printPattern: function(line, canvas) {
        var ctx = canvas.getContext("2d"), i;

        canvas.width = line.length;
        ctx.fillColor = "black";
        for ( i = 0; i < line.length; i++) {
            if (line[i] === 1) {
                ctx.fillRect(i, 0, 1, 100);
            }
        }
    }
};

export default Bresenham;