opencv 等比例縮放圖像（圖像尺寸不變）

效果圖如下：

變換前：

變換後：

代碼如下：

struct object_rect {
	int x;
	int y;
	int width;
	int height;
};

int resize_uniform(Mat &src, Mat &dst, Size dst_size, object_rect &effect_area)
{
	int w = src.cols;
	int h = src.rows;
	int dst_w = dst_size.width;
	int dst_h = dst_size.height;
	std::cout << "src: (" << h << ", " << w << ")" << std::endl;
	dst = Mat(Size(dst_w, dst_h), CV_8UC1, Scalar(1));

	float ratio_src = w*1.0 / h;
	float ratio_dst = dst_w*1.0 / dst_h;

	int tmp_w = 0;
	int tmp_h = 0;
	if (ratio_src > ratio_dst) {
		tmp_w = dst_w;
		tmp_h = floor((dst_w*1.0 / w) * h);
	}
	else if (ratio_src < ratio_dst) {
		tmp_h = dst_h;
		tmp_w = floor((dst_h*1.0 / h) * w);
	}
	else {
		resize(src, dst, dst_size);
		effect_area.x = 0;
		effect_area.y = 0;
		effect_area.width = dst_w;
		effect_area.height = dst_h;
		return 0;
	}

	std::cout << "tmp: (" << tmp_h << ", " << tmp_w << ")" << std::endl;
	Mat tmp;
	resize(src, tmp, Size(tmp_w, tmp_h));
	tmp.convertTo(tmp,CV_8UC1);
	
	if (tmp_w != dst_w) { //高對齊，寬沒對齊
		int index_w = floor((dst_w - tmp_w) / 2.0);
		std::cout << "index_w: " << index_w << std::endl;
		for (int i = 0; i<dst_h; i++) {
			memcpy(dst.data + i*dst_w + index_w, tmp.data + i*tmp_w, tmp_w);
		}
		effect_area.x = index_w;
		effect_area.y = 0;
		effect_area.width = tmp_w;
		effect_area.height = tmp_h;
	}
	else if (tmp_h != dst_h) { //寬對齊， 高沒有對齊
		int index_h = floor((dst_h - tmp_h) / 2.0);
		std::cout << "index_h: " << index_h << std::endl;
		memcpy(dst.data + index_h*dst_w, tmp.data, tmp_w*tmp_h);
		effect_area.x = 0;
		effect_area.y = index_h;
		effect_area.width = tmp_w;
		effect_area.height = tmp_h;
	}
	else {
		printf("error\n");
	}
	return 0;
}

void main()
{
   ....
   //OriMat 爲圖一的mat格式數據

   int nSmallWidth = width / 4.0*3.0;
   int nSmallHeight = height / 4.0*3.0;
   Mat dst;
   object_rect res_area;
		
  (void)resize_uniform(OriMat, dst, Size(nSmallWidth, nSmallHeight), res_area);

  SmallSlicebwMatrix.resize(nSmallHeight, nSmallWidth);//習慣使用eigen出來矩陣，所以轉換成 
                                                    //    eigen 格式的矩陣
  cv2eigen(dst, SmallSlicebwMatrix);

  OriSlicebwMatrix.setOnes();
  int nWidthBeg = (width - nSmallWidth)*1.0 / 2.0;
  int nHeightBeg = (height - nSmallHeight)*1.0 / 2.0;
  for (int i = 0; i < nSmallHeight; i++)
  {
	 for (int j = 0; j < nSmallWidth; j++)
	{
		OriSlicebwMatrix(i + nHeightBeg, j + nWidthBeg) = SmallSlicebwMatrix(i, j); 
       //OriSlicebwMatrix  即爲圖2
	}
}

}