如何在opencv中的实际位置获取图像像素？

问题描述：

我想检索图像中像素的rgb。
但该位置不是整数位置，而是实数值（x，y）。
我想要一个双线性插值。
我怎么能这样做opencv？

I want to retrieve the rgb of a pixel in the image. But the location is not integer location but real values (x,y). I want a bilinear interpolated value. How could I do it opencv?

非常感谢

答

子像素访问没有简单的功能，但我可以建议你几个选项：

There is no simple function for subpixel access but I can suggest you few options:

使用 getRectSubPix 并提取1个像素区域：

Use getRectSubPix and extract 1 pixel region:

cv::Vec3b getColorSubpix(const cv::Mat& img, cv::Point2f pt)
{
    cv::Mat patch;
    cv::getRectSubPix(img, cv::Size(1,1), pt, patch);
    return patch.at<cv::Vec3b>(0,0);
}

使用更灵活但不太精确重新映射：

cv::Vec3b getColorSubpix(const cv::Mat& img, cv::Point2f pt)
{
    cv::Mat patch;
    cv::remap(img, patch, cv::Mat(1, 1, CV_32FC2, &pt), cv::noArray(),
        cv::INTER_LINEAR, cv::BORDER_REFLECT_101);
    return patch.at<cv::Vec3b>(0,0);
}

自己实施双线性插值，因为它不是火箭科学：

Implement bilinear interpolation yourself, as it is not a rocket science:

cv::Vec3b getColorSubpix(const cv::Mat& img, cv::Point2f pt)
{
    assert(!img.empty());
    assert(img.channels() == 3);

    int x = (int)pt.x;
    int y = (int)pt.y;

    int x0 = cv::borderInterpolate(x,   img.cols, cv::BORDER_REFLECT_101);
    int x1 = cv::borderInterpolate(x+1, img.cols, cv::BORDER_REFLECT_101);
    int y0 = cv::borderInterpolate(y,   img.rows, cv::BORDER_REFLECT_101);
    int y1 = cv::borderInterpolate(y+1, img.rows, cv::BORDER_REFLECT_101);

    float a = pt.x - (float)x;
    float c = pt.y - (float)y;

    uchar b = (uchar)cvRound((img.at<cv::Vec3b>(y0, x0)[0] * (1.f - a) + img.at<cv::Vec3b>(y0, x1)[0] * a) * (1.f - c)
                           + (img.at<cv::Vec3b>(y1, x0)[0] * (1.f - a) + img.at<cv::Vec3b>(y1, x1)[0] * a) * c);
    uchar g = (uchar)cvRound((img.at<cv::Vec3b>(y0, x0)[1] * (1.f - a) + img.at<cv::Vec3b>(y0, x1)[1] * a) * (1.f - c)
                           + (img.at<cv::Vec3b>(y1, x0)[1] * (1.f - a) + img.at<cv::Vec3b>(y1, x1)[1] * a) * c);
    uchar r = (uchar)cvRound((img.at<cv::Vec3b>(y0, x0)[2] * (1.f - a) + img.at<cv::Vec3b>(y0, x1)[2] * a) * (1.f - c)
                           + (img.at<cv::Vec3b>(y1, x0)[2] * (1.f - a) + img.at<cv::Vec3b>(y1, x1)[2] * a) * c);

    return cv::Vec3b(b, g, r);
}

如何在opencv中的实际位置获取图像像素？

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