OpenCv 014---圖像插值（Image interpolation）

1 前備知識

圖像在進行幾何變換、透視變換等場景時需要插值計算新像素的像素值。

圖像處理之三種常見雙立方插值算法 - CSDN博客

圖像放縮之雙立方插值 - CSDN博客

圖像放縮之雙線性內插值 - CSDN博客

圖像處理之Lanczos采樣放縮算法 - CSDN博客

（1）INTER_NEAREST最鄰近插值

將離新像素所在位置最近的像素像素值賦值給新像素。計算亮最小。

（2）雙線性插值

x、y方向臨近像素取乘以相應權重並相加賦值給i新的像素值。

（3）雙立方插值

精度更高，計算量最大，取附近十六個點加權取像素值。

（4）INTER_LANCZOS4

附近像素及原像素加權取值。

2 所用到的主要OpenCv API

/** @brief 對一副圖像指定x，y方向上的縮放比例進行縮放。

@code
// explicitly specify dsize=dst.size(); fx and fy will be computed from that.
resize(src, dst, dst.size(), 0, 0, interpolation);
@endcode
If you want to decimate the image by factor of 2 in each direction, you can call the function this
way:
@code
// specify fx and fy and let the function compute the destination image size.
resize(src, dst, Size(), 0.5, 0.5, interpolation);
@endcode
To shrink an image, it will generally look best with #INTER_AREA interpolation, whereas to
enlarge an image, it will generally look best with c#INTER_CUBIC (slow) or #INTER_LINEAR
(faster but still looks OK).

@param src input image.
@param dst output image; it has the size dsize (when it is non-zero) or the size computed from
src.size(), fx, and fy; the type of dst is the same as of src.
@param dsize output image size; if it equals zero, it is computed as:
\f[\texttt{dsize = Size(round(fx*src.cols), round(fy*src.rows))}\f]
Either dsize or both fx and fy must be non-zero.
@param fx scale factor along the horizontal axis; when it equals 0, it is computed as
\f[\texttt{(double)dsize.width/src.cols}\f]
@param fy scale factor along the vertical axis; when it equals 0, it is computed as
\f[\texttt{(double)dsize.height/src.rows}\f]
@param interpolation interpolation method, see #InterpolationFlags

@sa warpAffine, warpPerspective, remap
*/

CV_EXPORTS_W void resize( InputArray src, OutputArray dst,
                          Size dsize, double fx = 0, double fy = 0,
                          int interpolation = INTER_LINEAR );

3 程序代碼

#include"opencv2\opencv.hpp"
#include<iostream>

using namespace std;
using namespace cv;

int main(int argc, char** argv)
{
    Mat src = imread("G:\\CVworkstudy\\program_wwx\\研習社140課時\\ZhaiZhigang140\\colormap.png");
    if (src.empty())
    {
        printf("Could not load image...\n");
        return -1;
    }
    imshow("srcImg", src);
    Mat dst = Mat::zeros(src.size(), src.type());
    double fx = 0, fy = 0;
    int height = src.rows;
    int width = src.cols;
    //最鄰近插值
    resize(src, dst, Size(0, 0), 0.5, 0.5, INTER_NEAREST);//如果Size(0,0),則圖像大小為Size(width*fx height*fy)
    imshow("NEAREST", dst);
    //雙線性插值
    resize(src, dst, Size(width * 2, height * 2), fx, fy, INTER_LINEAR);
    imshow("LineNear", dst);
    //雙立方插值
    resize(src, dst, Size(width * 2, height * 2), fx, fy, INTER_CUBIC);
    imshow("CUBIC", dst);
    //LANCZOS插值
    resize(src, dst, Size(width * 2, height * 2), fx, fy, INTER_LANCZOS4);
    imshow("LANCZOS", dst);

    waitKey(0);
    return 0;
}

4 運行結果

5 擴展及注意事項

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