代碼如下:
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;
}

有個問題，假如圖片是灰色的跟原圖進行比較，那么要比較相似度，需要將圖片都轉成灰色的，即使用上面代碼的gray函數來處理

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