5、兰索斯插值:由相邻的8*8像素计算得出,公式类似于双线性
- int iscale_x = cv::saturate_cast<int>(scale_x);
- int iscale_y = cv::saturate_cast<int>(scale_y);
- for (int j = 0; j < matDst1.rows; ++j)
- {
- float fy = (float)((j + 0.5) * scale_y - 0.5);
- int sy = cvFloor(fy);
- fy -= sy;
- sy = std::min(sy, matSrc.rows - 5);
- sy = std::max(3, sy);
- const double s45 = 0.70710678118654752440084436210485;
- const double cs[][2] = {{1, 0}, {-s45, -s45}, {0, 1}, {s45, -s45}, {-1, 0}, {s45, s45}, {0, -1}, {-s45, s45}};
- float coeffsY[8];
- if (fy < FLT_EPSILON) {
- for (int t = 0; t < 8; t++)
- coeffsY[t] = 0;
- coeffsY[3] = 1;
- } else {
- float sum = 0;
- double y0 = -(fy + 3) * CV_PI * 0.25, s0 = sin(y0), c0 = cos(y0);
- for (int t = 0; t < 8; ++t)
- {
- double dy = -(fy + 3 -t) * CV_PI * 0.25;
- coeffsY[t] = (float)((cs[t][0] * s0 + cs[t][1] * c0) / (dy * dy));
- sum += coeffsY[t];
- }
- sum = 1.f / sum;
- for (int t = 0; t < 8; ++t)
- coeffsY[t] *= sum;
- }
- short cbufY[8];
- cbufY[0] = cv::saturate_cast<short>(coeffsY[0] * 2048);
- cbufY[1] = cv::saturate_cast<short>(coeffsY[1] * 2048);
- cbufY[2] = cv::saturate_cast<short>(coeffsY[2] * 2048);
- cbufY[3] = cv::saturate_cast<short>(coeffsY[3] * 2048);
- cbufY[4] = cv::saturate_cast<short>(coeffsY[4] * 2048);
- cbufY[5] = cv::saturate_cast<short>(coeffsY[5] * 2048);
- cbufY[6] = cv::saturate_cast<short>(coeffsY[6] * 2048);
- cbufY[7] = cv::saturate_cast<short>(coeffsY[7] * 2048);
- for (int i = 0; i < matDst1.cols; ++i)
- {
- float fx = (float)((i + 0.5) * scale_x - 0.5);
- int sx = cvFloor(fx);
- fx -= sx;
- if (sx < 3) {
- fx = 0, sx = 3;
- }
- if (sx >= matSrc.cols - 5) {
- fx = 0, sx = matSrc.cols - 5;
- }
- float coeffsX[8];
- if (fx < FLT_EPSILON) {
- for ( int t = 0; t < 8; t++ )
- coeffsX[t] = 0;
- coeffsX[3] = 1;
- } else {
- float sum = 0;
- double x0 = -(fx + 3) * CV_PI * 0.25, s0 = sin(x0), c0 = cos(x0);
- for (int t = 0; t < 8; ++t)
- {
- double dx = -(fx + 3 -t) * CV_PI * 0.25;
- coeffsX[t] = (float)((cs[t][0] * s0 + cs[t][1] * c0) / (dx * dx));
- sum += coeffsX[t];
- }
- sum = 1.f / sum;
- for (int t = 0; t < 8; ++t)
- coeffsX[t] *= sum;
- }
- short cbufX[8];
- cbufX[0] = cv::saturate_cast<short>(coeffsX[0] * 2048);
- cbufX[1] = cv::saturate_cast<short>(coeffsX[1] * 2048);
- cbufX[2] = cv::saturate_cast<short>(coeffsX[2] * 2048);
- cbufX[3] = cv::saturate_cast<short>(coeffsX[3] * 2048);
- cbufX[4] = cv::saturate_cast<short>(coeffsX[4] * 2048);
- cbufX[5] = cv::saturate_cast<short>(coeffsX[5] * 2048);
- cbufX[6] = cv::saturate_cast<short>(coeffsX[6] * 2048);
- cbufX[7] = cv::saturate_cast<short>(coeffsX[7] * 2048);
- for (int k = 0; k < matSrc.channels(); ++k)
- {
- matDst1.at<cv::Vec3b>(j, i)[k] = abs((matSrc.at<cv::Vec3b>(sy-3, sx-3)[k] * cbufX[0] * cbufY[0] + matSrc.at<cv::Vec3b>(sy-2, sx-3)[k] * cbufX[0] * cbufY[1] +
- matSrc.at<cv::Vec3b>(sy-1, sx-3)[k] * cbufX[0] * cbufY[2] + matSrc.at<cv::Vec3b>(sy, sx-3)[k] * cbufX[0] * cbufY[3] +
- matSrc.at<cv::Vec3b>(sy+1, sx-3)[k] * cbufX[0] * cbufY[4] + matSrc.at<cv::Vec3b>(sy+2, sx-3)[k] * cbufX[0] * cbufY[5] +
- matSrc.at<cv::Vec3b>(sy+3, sx-3)[k] * cbufX[0] * cbufY[6] + matSrc.at<cv::Vec3b>(sy+4, sx-3)[k] * cbufX[0] * cbufY[7] +
- matSrc.at<cv::Vec3b>(sy-3, sx-2)[k] * cbufX[1] * cbufY[0] + matSrc.at<cv::Vec3b>(sy-2, sx-2)[k] * cbufX[1] * cbufY[1] +
- matSrc.at<cv::Vec3b>(sy-1, sx-2)[k] * cbufX[1] * cbufY[2] + matSrc.at<cv::Vec3b>(sy, sx-2)[k] * cbufX[1] * cbufY[3] +
- matSrc.at<cv::Vec3b>(sy+1, sx-2)[k] * cbufX[1] * cbufY[4] + matSrc.at<cv::Vec3b>(sy+2, sx-2)[k] * cbufX[1] * cbufY[5] +
- matSrc.at<cv::Vec3b>(sy+3, sx-2)[k] * cbufX[1] * cbufY[6] + matSrc.at<cv::Vec3b>(sy+4, sx-2)[k] * cbufX[1] * cbufY[7] +
- matSrc.at<cv::Vec3b>(sy-3, sx-1)[k] * cbufX[2] * cbufY[0] + matSrc.at<cv::Vec3b>(sy-2, sx-1)[k] * cbufX[2] * cbufY[1] +
- matSrc.at<cv::Vec3b>(sy-1, sx-1)[k] * cbufX[2] * cbufY[2] + matSrc.at<cv::Vec3b>(sy, sx-1)[k] * cbufX[2] * cbufY[3] +
- matSrc.at<cv::Vec3b>(sy+1, sx-1)[k] * cbufX[2] * cbufY[4] + matSrc.at<cv::Vec3b>(sy+2, sx-1)[k] * cbufX[2] * cbufY[5] +
- matSrc.at<cv::Vec3b>(sy+3, sx-1)[k] * cbufX[2] * cbufY[6] + matSrc.at<cv::Vec3b>(sy+4, sx-1)[k] * cbufX[2] * cbufY[7] +
- matSrc.at<cv::Vec3b>(sy-3, sx)[k] * cbufX[3] * cbufY[0] + matSrc.at<cv::Vec3b>(sy-2, sx)[k] * cbufX[3] * cbufY[1] +
- matSrc.at<cv::Vec3b>(sy-1, sx)[k] * cbufX[3] * cbufY[2] + matSrc.at<cv::Vec3b>(sy, sx)[k] * cbufX[3] * cbufY[3] +
- matSrc.at<cv::Vec3b>(sy+1, sx)[k] * cbufX[3] * cbufY[4] + matSrc.at<cv::Vec3b>(sy+2, sx)[k] * cbufX[3] * cbufY[5] +
- matSrc.at<cv::Vec3b>(sy+3, sx)[k] * cbufX[3] * cbufY[6] + matSrc.at<cv::Vec3b>(sy+4, sx)[k] * cbufX[3] * cbufY[7] +
- matSrc.at<cv::Vec3b>(sy-3, sx+1)[k] * cbufX[4] * cbufY[0] + matSrc.at<cv::Vec3b>(sy-2, sx+1)[k] * cbufX[4] * cbufY[1] +
- matSrc.at<cv::Vec3b>(sy-1, sx+1)[k] * cbufX[4] * cbufY[2] + matSrc.at<cv::Vec3b>(sy, sx+1)[k] * cbufX[4] * cbufY[3] +
- matSrc.at<cv::Vec3b>(sy+1, sx+1)[k] * cbufX[4] * cbufY[4] + matSrc.at<cv::Vec3b>(sy+2, sx+1)[k] * cbufX[4] * cbufY[5] +
- matSrc.at<cv::Vec3b>(sy+3, sx+1)[k] * cbufX[4] * cbufY[6] + matSrc.at<cv::Vec3b>(sy+4, sx+1)[k] * cbufX[4] * cbufY[7] +
- matSrc.at<cv::Vec3b>(sy-3, sx+2)[k] * cbufX[5] * cbufY[0] + matSrc.at<cv::Vec3b>(sy-2, sx+2)[k] * cbufX[5] * cbufY[1] +
- matSrc.at<cv::Vec3b>(sy-1, sx+2)[k] * cbufX[5] * cbufY[2] + matSrc.at<cv::Vec3b>(sy, sx+2)[k] * cbufX[5] * cbufY[3] +
- matSrc.at<cv::Vec3b>(sy+1, sx+2)[k] * cbufX[5] * cbufY[4] + matSrc.at<cv::Vec3b>(sy+2, sx+2)[k] * cbufX[5] * cbufY[5] +
- matSrc.at<cv::Vec3b>(sy+3, sx+2)[k] * cbufX[5] * cbufY[6] + matSrc.at<cv::Vec3b>(sy+4, sx+2)[k] * cbufX[5] * cbufY[7] +
- matSrc.at<cv::Vec3b>(sy-3, sx+3)[k] * cbufX[6] * cbufY[0] + matSrc.at<cv::Vec3b>(sy-2, sx+3)[k] * cbufX[6] * cbufY[1] +
- matSrc.at<cv::Vec3b>(sy-1, sx+3)[k] * cbufX[6] * cbufY[2] + matSrc.at<cv::Vec3b>(sy, sx+3)[k] * cbufX[6] * cbufY[3] +
- matSrc.at<cv::Vec3b>(sy+1, sx+3)[k] * cbufX[6] * cbufY[4] + matSrc.at<cv::Vec3b>(sy+2, sx+3)[k] * cbufX[6] * cbufY[5] +
- matSrc.at<cv::Vec3b>(sy+3, sx+3)[k] * cbufX[6] * cbufY[6] + matSrc.at<cv::Vec3b>(sy+4, sx+3)[k] * cbufX[6] * cbufY[7] +
- matSrc.at<cv::Vec3b>(sy-3, sx+4)[k] * cbufX[7] * cbufY[0] + matSrc.at<cv::Vec3b>(sy-2, sx+4)[k] * cbufX[7] * cbufY[1] +
- matSrc.at<cv::Vec3b>(sy-1, sx+4)[k] * cbufX[7] * cbufY[2] + matSrc.at<cv::Vec3b>(sy, sx+4)[k] * cbufX[7] * cbufY[3] +
- matSrc.at<cv::Vec3b>(sy+1, sx+4)[k] * cbufX[7] * cbufY[4] + matSrc.at<cv::Vec3b>(sy+2, sx+4)[k] * cbufX[7] * cbufY[5] +
- matSrc.at<cv::Vec3b>(sy+3, sx+4)[k] * cbufX[7] * cbufY[6] + matSrc.at<cv::Vec3b>(sy+4, sx+4)[k] * cbufX[7] * cbufY[7] ) >> 22);// 4194304
- }
- }
- }
- cv::imwrite("Lanczos_1.jpg", matDst1);
- cv::resize(matSrc, matDst2, matDst1.size(), 0, 0, 4);
- cv::imwrite("Lanczos_2.jpg", matDst2);
以上代码的实现结果与cv::resize函数相同,但是执行效率非常低,只是为了详细说明插值过程。OpenCV中默认采用C++ Concurrency进行优化加速,你也可以采用TBB、OpenMP等进行优化加速。