opencv函数GaussianBlur，pyrDown，pyrUp深究

最新推荐文章于 2025-06-12 09:25:30 发布

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本文详细介绍了如何手动实现GaussianBlur、pyrDown与pyrUp算法，并通过与OpenCV库中对应函数的结果进行对比，验证了实现的正确性。

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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。