数字图像处理基础代码（C语言）

① Sobel算子检测边缘

void CDemoView::Onsobel()
{
    CDemoDoc *pDoc = GetDocument();
    HDIB dib = pDoc->GetHDIB();
    LPSTR lpDIB = (LPSTR)::GlobalLock((HGLOBAL)dib);
    LPBITMAPINFOHEADER phead = (LPBITMAPINFOHEADER)lpDIB; //信息头指针

    int biByteCount = phead->biBitCount / 8; //每像素字节数
    if (biByteCount == 3)
    {
        ::GlobalUnlock(dib);
        return;
    } //彩色图不做处理
    int w = phead->biWidth;
    int h = phead->biHeight;
    int lineByte = (biByteCount * w + 3) / 4 * 4;
    unsigned char *lpDIBBits = (unsigned char *)::FindDIBBits(lpDIB); //像素位置指针,unsigned char取值范围是0~255(一个字节)
    unsigned char *buf = new unsigned char[w*h]; //新内存存放运算结果
    unsigned char c[2]; //存2个模板的卷积结果
    unsigned char a[8]; //取邻域元素
    int r; //存卷积结果
    for (int i = 1; i < h - 1; i++) {
        for (int j = 1; j < w - 1; j++) {
            a[0] = *(lpDIBBits + (i + 1) * lineByte + j - 1);
            a[1] = *(lpDIBBits + (i + 1) * lineByte + j);
            a[2] = *(lpDIBBits + (i + 1) * lineByte + j + 1);
            a[3] = *(lpDIBBits + i * lineByte + j + 1);
            a[4] = *(lpDIBBits + (i - 1) * lineByte + j + 1);
            a[5] = *(lpDIBBits + (i - 1) * lineByte + j);
            a[6] = *(lpDIBBits + (i - 1) * lineByte + j - 1);
            a[7] = *(lpDIBBits + i * lineByte + j - 1);
            c[0] = abs(-a[0] + a[2] + a[3] * 2 + a[4] - a[6] - a[7] * 2);
            c[1] = abs(a[0] + a[1] * 2 + a[2] - a[4] - a[5] * 2 - a[6]);
            r = 2 * pow(c[0] * c[0] + c[1] * c[1], 0.5); //综合垂直与水平两个方向，乘2再放大一下，结果变亮一些
            if (r > 255)
                r = 255;
            *(buf + i * w + j) = r;
        }
    }
    for (int i = 1; i < h - 1; i++) {
        for (int j = 1; j < w - 1; j++) {
            *(lpDIBBits + i * lineByte + j) = *(buf + i * w + j);
        }
    }

    delete[]buf;
    ::GlobalUnlock(dib);
    Invalidate(); //区域重绘

}

② 直方图均衡

void CDemoView::OnHistEqual()
{
    CDemoDoc *pDoc = GetDocument();
    HDIB dib = pDoc->GetHDIB();
    LPSTR lpDIB = (LPSTR)::GlobalLock((HGLOBAL)dib);
    LPBITMAPINFOHEADER phead = (LPBITMAPINFOHEADER)lpDIB; //信息头指针

    int biByteCount = phead->biBitCount / 8; //每像素字节数
    if (biByteCount == 3)
    {
        ::GlobalUnlock(dib);
        return;
    } //彩色图不做处理
    int w = phead->biWidth;
    int h = phead->biHeight;
    int lineByte = (biByteCount * w + 3) / 4 * 4;
    unsigned char *lpDIBBits = (unsigned char *)::FindDIBBits(lpDIB); //像素位置指针,unsigned char取值范围是0~255(一个字节)

    double p[256];
    for (int i = 0; i < 256; i++) {
        p[i] = 0;
    }
    unsigned char value[256];
    //统计直方图
    unsigned char idx;
    for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
            idx = *(lpDIBBits + i * lineByte + j);
            p[idx] += 1.0 / (w*h);
        }
    }
    //累加
    for (int i = 1; i < 256; i++) {
        p[i] += p[i - 1];
    }
    //计算新的灰度值
    for (int i = 0; i < 256; i++) {
        value[i] = (unsigned char)(p[i] * 255);
    }
    for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
            idx = *(lpDIBBits + i * lineByte + j);
            *(lpDIBBits + i * lineByte + j) = value[idx];
        }
    }

    ::GlobalUnlock(dib);
    Invalidate(); //区域重绘
}

③ 大津阈值

void CDemoView::Onotsu()
{
    CDemoDoc *pDoc = GetDocument();
    HDIB dib = pDoc->GetHDIB();
    LPSTR lpDIB = (LPSTR)::GlobalLock((HGLOBAL)dib);
    LPBITMAPINFOHEADER phead = (LPBITMAPINFOHEADER)lpDIB; //信息头指针

    int biByteCount = phead->biBitCount / 8; //每像素字节数
    if (biByteCount == 3)
    {
        ::GlobalUnlock(dib);
        return;
    } //彩色图不做处理
    int w = phead->biWidth;
    int h = phead->biHeight;
    int lineByte = (biByteCount * w + 3) / 4 * 4;
    unsigned char *lpDIBBits = (unsigned char *)::FindDIBBits(lpDIB); //像素位置指针,unsigned char取值范围是0~255(一个字节)

    //统计直方图
    float p[256];
    for (int i = 0; i < 256; i++) {
        p[i] = 0;
    }
    unsigned char idx;
    for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
            idx = *(lpDIBBits + i * lineByte + j);
            p[idx] += 1.0 / (w*h);
        }
    }

    //计算全图均值
    float u = 0;
    for (int i = 0; i < 256; i++) {
        u += p[i] * i;
    }

    //统计类间最大方差diff(th)
    float diff = 0;
    float diffmax = 0;
    int T = 0;
    for (int th = 1; th < 256; th++) {     //分为小于和大于等于两部分
        float w0 = 0;
        float w1 = 0;
        float u0 = 0;
        float u1 = 0;
        //w0 and u0
        for (int i = 0; i < th; i++) {
            w0 += p[i];
            u0 += p[i] * i;
        }
        if (w0 == 0.0) //注意这里如果前半部分没有像素，就不能当作阈值
            continue;
        else
            u0 = u0 / w0;
        //w1 and u1
        for (int i = th; i < 256; i++) {
            u1 += p[i] * i;
        }
        w1 = 1.0 - w0;
        if (w1 == 0.0)
            continue;
        else
            u1 = u1 / w1;
        //类间方差diff
        diff = w0 * pow((u0 - u), 2) + w1 * pow((u1 - u), 2);
        //diff = w0 * w1 * pow((u0 - u1), 2);
        if (diffmax < diff) {
            diffmax = diff;
            T = th;
        }
    }

    //阈值分割
    for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
            if (*(lpDIBBits + i * lineByte + j) < T)
                *(lpDIBBits + i * lineByte + j) = 0;
            else
                *(lpDIBBits + i * lineByte + j) = 255;
        }
    }

    ::GlobalUnlock(dib);
    Invalidate(); //区域重绘
}

：
（1）大津阈值算法中，注意遍历的时候如果小于原图灰度最小值或者大于灰度最大值，则不取；
（2）大津阈值算法中，两部分的均值计算要思考正确；
（3）C语言给变量赋值的时候要考虑好变量的数据类型；
（4）在形如x += *的代码中，要处理好x的初值；
（5）傅里叶反变换去噪时，实部和虚部都要做处理。

麻瓜写于2018/11/30