OpenCV 像素访问指针与 at() - 不同的值

Question

我在尝试访问像素时遇到了奇怪的行为，如下所示：

void Dbscan::regionQuery(int i, int j, std::vector<Point>* res) const {
// check rect. grid around center point
const size_t row_min = std::max(0, i-eps_);
const size_t row_max = std::min(n_rows_, i+eps_+1);
const size_t col_min = std::max(0, j-eps_);
const size_t col_max = std::min(n_cols_, j+eps_+1);
assert(masked_img_.depth() == CV_8UC1);
for (int m = row_min; m<row_max; ++m) {
    const uchar* mask_ptr = masked_img_.ptr(m);
    for (int n = col_min; n<col_max; ++n) {
        assert(*mask_ptr == masked_img_.at<uchar>(m, n));
        if (masked_img_.at<uchar>(m, n) == 255) {
            res->emplace_back(Point(m,n));
        }
        mask_ptr++;
    }
}

基本上，如图所示的第二个断言失败了，我对发生了什么一无所知。有谁知道如何最好地解决上述问题？

此致问候

菲利克斯

Answer 1

cv::Mat::ptr returns a pointer to the beginning of the row from the argument, which is an address of an element in the first column of this row. cv::Mat::at returns 对参数中行和列中元素的引用。在您的代码中，行匹配，但列不匹配（除非您的 col_min 评估为 0），因此您需要将指针从 cv::Mat::ptr n 元素移动以匹配您的列嗯：

for (int m = row_min; m<row_max; ++m) {
    const uchar* mask_ptr = masked_img_.ptr(m);
    for (int n = col_min; n<col_max; ++n) {
        assert(*(mask_ptr + n) == masked_img_.at<uchar>(m, n));
        if (masked_img_.at<uchar>(m, n) == 255) {
            res->emplace_back(Point(m,n));
        }
    }
}

OpenCV 像素访问指针与 at() - 不同的值

OpenCV pixel access pointr vs. at() - Different values

c++

opencv

roi

pixel