opencv函数GaussianBlur，pyrDown，pyrUp深究

本文主要是介绍opencv函数GaussianBlur，pyrDown，pyrUp深究，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

通常在使用GaussianBlur,pyrDown，pyrUp的时候都不会深究的内部实现，最近想自己实现一下,看看会遇到哪些问题，然后将结果和opencv的函数运行结果进行对比。

C++: void GaussianBlur(InputArray src, OutputArray dst, Size ksize, double sigmaX, double sigmaY=0, int borderType=BORDER_DEFAULT )

从GaussianBlur的参数可以看出,有sigmaX 和sigmaY, 二维高斯核使用的是分别在X和Y方向进行一维高斯核卷积来模拟二维高斯核的效果。

对于边界问题，BORDER_DEFAULT 是指：pixel[-1]使用pixel[1]的像素值来代替，pixel[-2] = pixel[2],pixel[width] = pixel[width - 2],依此类推(如果pixel[0]，pixel[width -1]为边界的话) 。

	for (int row = 0 ;row <src.rows ;row++)//x orientation{for (int col = 0 ; col <src.cols; col++){float sumRed = 0,sumGreen = 0,sumBlue = 0;for (int subcol = -win_size;subcol<=win_size;subcol++){int srccol = col+subcol;if (srccol<0){srccol *= -1;}if (srccol>=src.cols){srccol = src.cols*2 - srccol - 2;}sumRed += kernel[subcol+win_size]*src.at<Vec3b>(row,srccol)[2];sumGreen += kernel[subcol+win_size]*src.at<Vec3b>(row,srccol)[1];sumBlue += kernel[subcol+win_size]*src.at<Vec3b>(row,srccol)[0];}temp.at<Vec3b>(row,col)[2] = sumRed;temp.at<Vec3b>(row,col)[1] = sumGreen;temp.at<Vec3b>(row,col)[0] = sumBlue;}}for (int row = 0 ;row <src.rows ;row++)//y orientation{for (int col = 0 ; col <src.cols; col++){float sumRed = 0,sumGreen = 0,sumBlue = 0;for (int subrow = -win_size;subrow<=win_size;subrow++){int srcrow = row+subrow;if (srcrow<0){srcrow *= -1;}if (srcrow>=src.rows){srcrow = src.rows*2 - srcrow - 2;;}sumRed += kernel[subrow+win_size]*temp.at<Vec3b>(srcrow,col)[2];sumGreen += kernel[subrow+win_size]*temp.at<Vec3b>(srcrow,col)[1];sumBlue += kernel[subrow+win_size]*temp.at<Vec3b>(srcrow,col)[0];}result.at<Vec3b>(row,col)[2] = sumRed;result.at<Vec3b>(row,col)[1] = sumGreen;result.at<Vec3b>(row,col)[0] = sumBlue;}}

C++: void pyrDown(InputArray src, OutputArray dst, const Size& dstsize=Size())

pyrDown 是降采样，分两步进行。

第一步：对src图像进行模糊，使用的模糊核不是高斯核，而是这样一个核函数：

第二步：模糊之后的图像去除所有偶数行和偶数列。

void GassianPyramid::downSampleFunc(Mat src, Mat& result)
{int width = src.cols;int height = src.rows;int ow = width/2;  int oh = height/2;  result.create(Size(ow,oh),src.type());float tempArr[5][5]={1,4,6,4,1,4,16,24,16,4,6,24,36,24,6,4,16,24,16,4,1,4,6,4,1};for (int i = 0;i<5;i++){for (int j = 0; j<5; j++){tempArr[i][j] /=256;}}Mat temp;temp.create(Size(src.cols,src.rows),src.type());for (int row = 0 ;row <src.rows ;row++){for (int col = 0 ; col <src.cols; col++){float sumRed = 0,sumGreen = 0,sumBlue = 0;for (int subrow = -win_size;subrow<=win_size;subrow++){int srcrow = row+subrow;if (srcrow<0){srcrow *= -1;}if (srcrow>=src.rows){srcrow = (src.rows - 1) - (srcrow - (src.rows-1));}for (int subcol = -win_size;subcol<=win_size;subcol++){int srccol = col+subcol;if (srccol<0){srccol *= -1;}if (srccol>=src.cols){srccol = (src.cols - 1) - (srccol - (src.cols-1));}sumRed += tempArr[subrow+win_size][subcol+win_size]*src.at<Vec3b>(srcrow,srccol)[2];sumGreen += tempArr[subrow+win_size][subcol+win_size]*src.at<Vec3b>(srcrow,srccol)[1];sumBlue += tempArr[subrow+win_size][subcol+win_size]*src.at<Vec3b>(srcrow,srccol)[0];}}temp.at<Vec3b>(row,col)[2] = sumRed;temp.at<Vec3b>(row,col)[1] = sumGreen;temp.at<Vec3b>(row,col)[0] = sumBlue;}}int inRow=0, inCol = 0;  		for(int row=0; row<oh; row++) {  for(int col=0; col<ow; col++) {  inRow = 2* row;  inCol = 2* col;  if(inRow >= height) {  inRow = height;  }  if(inCol >= width) {  inCol = width;  }  result.at<Vec3b>(row,col)[2]= temp.at<Vec3b>(inRow,inCol)[2];result.at<Vec3b>(row,col)[1]= temp.at<Vec3b>(inRow,inCol)[1];result.at<Vec3b>(row,col)[0]= temp.at<Vec3b>(inRow,inCol)[0];}  }
}

C++: void pyrUp(InputArray src, OutputArray dst, const Size& dstsize=Size())

pyrUp是上采样，也是分两步进行。第一步：将图像在每个方向扩大为原来的两倍，新增的行和列以0填充。

第二步：将 上面降采样的高斯核*4和放大后的图像进行卷积。

void GassianPyramid::expendSampleFunc(Mat src, Mat& result)
{int width = src.cols;int height = src.rows;int ow = 2*width;  int oh =2*height; Mat temp;temp.create(Size(ow,oh),src.type());result.create(Size(ow,oh),src.type());for(int row=0; row<oh; row++) {  for(int col=0; col<ow; col++) {  int inRow = row/2;  int inCol = col/2;if(row - inRow*2 > 0 || col - inCol*2 > 0) {  temp.at<Vec3b>(row,col)[2] = 0;temp.at<Vec3b>(row,col)[1] = 0;temp.at<Vec3b>(row,col)[0] = 0;continue;} temp.at<Vec3b>(row,col)[2] = src.at<Vec3b>(inRow,inCol)[2];temp.at<Vec3b>(row,col)[1] = src.at<Vec3b>(inRow,inCol)[1];temp.at<Vec3b>(row,col)[0] = src.at<Vec3b>(inRow,inCol)[0];}  }  float tempArr[5][5]={1,4,6,4,1,4,16,24,16,4,6,24,36,24,6,4,16,24,16,4,1,4,6,4,1};for (int i = 0;i<5;i++){for (int j = 0; j<5; j++){tempArr[i][j] /=64;}}for (int row = 0 ;row <temp.rows ;row++){for (int col = 0 ; col <temp.cols; col++){float sumRed = 0,sumGreen = 0,sumBlue = 0;for (int subrow = -win_size;subrow<=win_size;subrow++){int srcrow = row+subrow;if (srcrow<0){srcrow *= -1;}if (srcrow>=temp.rows){srcrow = (temp.rows - 1) - (srcrow - (temp.rows-1));}for (int subcol = -win_size;subcol<=win_size;subcol++){int srccol = col+subcol;if (srccol<0){srccol *= -1;}if (srccol>=temp.cols){srccol = (temp.cols - 1) - (srccol - (temp.cols-1));}sumRed += tempArr[subrow+win_size][subcol+win_size]*temp.at<Vec3b>(srcrow,srccol)[2];sumGreen += tempArr[subrow+win_size][subcol+win_size]*temp.at<Vec3b>(srcrow,srccol)[1];sumBlue += tempArr[subrow+win_size][subcol+win_size]*temp.at<Vec3b>(srcrow,srccol)[0];}}result.at<Vec3b>(row,col)[2] = sumRed;result.at<Vec3b>(row,col)[1] = sumGreen;result.at<Vec3b>(row,col)[0] = sumBlue;}}
}

结果发现，和opencv自带的函数运行结果相同，证明结果正确。

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