ORBDetector.js

// require jsfeat

var options = {
	blur_size: 5,
    lap_thres: 30,
    eigen_thres: 25
}


var u_max = new Int32Array([15,15,15,15,14,14,14,13,13,12,11,10,9,8,6,3,0]);
 function ic_angle(img, px, py) {
                var half_k = 15; // half patch size
                var m_01 = 0, m_10 = 0;
                var src=img.data, step=img.cols;
                var u=0, v=0, center_off=(py*step + px)|0;
                var v_sum=0,d=0,val_plus=0,val_minus=0;

                // Treat the center line differently, v=0
                for (u = -half_k; u <= half_k; ++u)
                    m_10 += u * src[center_off+u];

                // Go line by line in the circular patch
                for (v = 1; v <= half_k; ++v) {
                    // Proceed over the two lines
                    v_sum = 0;
                    d = u_max[v];
                    for (u = -d; u <= d; ++u) {
                        val_plus = src[center_off+u+v*step];
                        val_minus = src[center_off+u-v*step];
                        v_sum += (val_plus - val_minus);
                        m_10 += u * (val_plus + val_minus);
                    }
                    m_01 += v * v_sum;
                }

                return Math.atan2(m_01, m_10);
}
	
function detect_keypoints(img, corners, max_allowed) {
               
	jsfeat.yape06.laplacian_threshold = options.lap_thres;
	jsfeat.yape06.min_eigen_value_threshold = options.eigen_thres;
		   
			   
    var count = jsfeat.yape06.detect(img, corners, 17);
                
    if(count > max_allowed) {
       jsfeat.math.qsort(corners, 0, count-1, function(a,b){return (b.score<a.score);});
       count = max_allowed;
    }

	 
    for(var i = 0; i < count; ++i) {
        corners[i].angle = ic_angle(img, corners[i].x, corners[i].y);
    }

    return count;
}
	
function ORBdescriptors(img){

	var w = img.width;
	var h = img.height;

	var canvas = document.createElement('canvas');
	canvas.width=w;
	canvas.height=h;
	var ctx = canvas.getContext('2d');


	img_u8 = new jsfeat.matrix_t(w, h, jsfeat.U8_t | jsfeat.C1_t);
	img_u8_smooth = new jsfeat.matrix_t(w, h, jsfeat.U8_t | jsfeat.C1_t);

	screen_descriptors = new jsfeat.matrix_t(32, 500, jsfeat.U8_t | jsfeat.C1_t);
	pattern_descriptors = [];
	ctx.drawImage(img, 0, 0, w, h);
	
	
	var imageData = ctx.getImageData(0, 0, w, h);
	
	 
	jsfeat.imgproc.grayscale(imageData.data, w, h, img_u8);

	jsfeat.imgproc.gaussian_blur(img_u8, img_u8_smooth, options.blur_size);

	
	var keypoints = [];

	var i = w*h;
	while(--i >= 0)
		keypoints[i] = new jsfeat.keypoint_t(0,0,0,0,-1);
		
	
	var num_keypoints = detect_keypoints(img_u8_smooth, keypoints, 1000);

	jsfeat.orb.describe(img_u8_smooth, keypoints, num_keypoints, screen_descriptors);
	
	for(var i=0;i<num_keypoints;i++)
		ctx.fillRect(keypoints[i].x-2,keypoints[i].y-2,4,4);
	
	
	var result = {points:[]};
	for(var i=0;i<num_keypoints;i++){
	
		var sub = Array.from(screen_descriptors.data.slice(i*32,(i+1)*32));
		result.points.push(Object.assign({},keypoints[i],{descriptor:sub}));
		
		}
	

	return {canvas:canvas, keypoints:result};
}