Binarization with Otsu Method

getThresh.cs

public int getThresh()
{
    int th = 0; //ループ用の閾値
    double num1, num2; //画素数
    double sum1, sum2; //和
    double m1, m2; //平均
    double va_b; //クラス間分散の二乗
    double max = 0; //va_bの最大値を保存しておく変数

    //ヒストグラムを生成していなければ弾く
    if (hist == null) return -1;

    //(th=0)の処理
    num1 = hist[0];
    sum1 = hist[0] * 0;
    m1 = num1 != 0 ? sum1 / num1 : 0;

    num2 = 0;
    sum2 = 0;
    m2 = 0;
    for (int i = 1; i < 256; i++)
    {
        num2 += hist[i];
        sum2 += hist[i] * i;
    }
    m2 = num2 != 0 ? sum2 / num2 : 0;

    va_b = (num1 * num2 * (m1 - m2) * (m1 - m2));
    max = va_b;
    //Debug.Log("0:"+va_b);

    //(th=1)以降の処理
    for (th = 1; th < 255; th++)
    {
        num1 += hist[th];
        num2 -= hist[th];
        sum1 += hist[th] * th;
        sum2 -= hist[th] * th;
        m1 = num1 != 0 ? sum1 / num1 : 0;
        m2 = num2 != 0 ? sum2 / num2 : 0;
        va_b = (num1 * num2 * (m1 - m2) * (m1 - m2));

        //Debug.Log(th+":"+va_b);
        if (max < va_b)
        {
            thresh = th;
            max = va_b;
        }
    }

    return thresh;
}