1D gaussian kernel

gaussianKernel1d.js

// based on https://warpycode.wordpress.com/2009/04/13/computing-a-1d-gaussian-kernel/
// see http://www.stat.wisc.edu/~mchung/teaching/MIA/reading/diffusion.gaussian.kernel.pdf.pdf for more info

var gaussianKernel1d = (function () {
    var sqr2pi = Math.sqrt(2 * Math.PI);

    return function gaussianKernel1d (size, sigma) {
        "use strict";

        // ensure size is even and prepare variables
        var width = (size / 2) | 0,
            kernel = new Array(width * 2 + 1),
            norm = 1.0 / (sqr2pi * sigma),
            coefficient = 2 * sigma * sigma,
            total = 0,
            x;

        // set values and increment total
        for (x = -width; x <= width; x++) {
            total += kernel[width + x] = norm * Math.exp(-x * x / coefficient);
        }

        // divide by total to make sure the sum of all the values is equal to 1
        for (x = 0; x < kernel.length; x++) {
            kernel[x] /= total;
        }

        return kernel;
    };
}());

module.exports = gaussianKernel1d;