function getHistogram(imageData) {     var arr = [];     for (var i = 0; i < 64; i++) {         arr[i] = 0;     }     var data = imageData.data;     var pow4 = Math.pow(4, 2);     for (var i = 0, len = data.length; i < len; i += 4) {         var red = (data[i] / 64) | 0;         var green = (data[i + 1] / 64) | 0;         var blue = (data[i + 2] / 64) | 0;         var index = red * pow4 + green * 4 + blue;         arr[index]++;     }     return arr; } function cosine(arr1, arr2) {     var axb = 0,         a = 0,         b = 0;     for (var i = 0, len = arr1.length; i < len; i++) {         axb += arr1[i] * arr2[i];         a += arr1[i] * arr1[i];         b += arr2[i] * arr2[i];     }     return axb / (Math.sqrt(a) * Math.sqrt(b)); } function gray(imgData) {     var data = imgData.data;     for (var i = 0, len = data.length; i < len; i += 4) {         var gray = parseInt((data[i] + data[i + 1] + data[i + 2]) / 3);         data[i + 2] = data[i + 1] = data[i] = gray;     }     return imgData; }