How to Reduce Noise using the Median Filter of Image Processing?
How To Reduce Noise Using The Median Filter Of Image Processing?¶
Introduction
The photograph has many noises. We can reduce the noise using the median filter. There are a 3 by 3 matrix matching the photograph. We do the amount of the pixels of the 3 by 3 matrix. Then, we divide by 9. The result is the center pixel value of the 3 by 3 matrix. We will rewrite the result into the photograph.
Equipment
Operation System: Microsoft Windows 7 (64 bit)
Development Utility: Microsoft Visual Studio 2010
Usage
// The loop of the median filter
for ( iI = 0; iI < 6; iI++ )
{
// The height of the image
for ( int iY = 1; iY < imageA->DibInfo->bmiHeader.biHeight - 1; iY++ )
{
// The width of the image
for ( int iX = 1; iX < imageA->DibInfo->bmiHeader.biWidth - 1; iX++ )
{
// Variables
dobFilterResult = 0;
intCount = 0;
// The height of the 3 by 3 matrix
for ( intFWY = -1; intFWY <= 1; intFWY++ )
{
// The width of the 3 by 3 matrix
for ( intFWX = -1; intFWX <= 1; intFWX++ )
{
// The index with 3 by 3 matrix. The bit depth is three. Because the bit depth is 24 bits.
// So we multiplied by three.
lIDXA = ( (iX+intFWX) * 3 ) + ( (iY+intFWY) * imageA->DibInfo->bmiHeader.biWidth * 3 );
// Get the pixel of the blue channel.
byteRGB_BA = imageA->DibArry[lIDXA+0];
// Get the pixel of the green channel.
byteRGB_GA = imageA->DibArry[lIDXA+1];
// Get the pixel of the red channel.
byteRGB_RA = imageA->DibArry[lIDXA+2];
// Transform RGB color space to gray scale.
dobYUV_YA = (0.299 * byteRGB_RA + 0.587 * byteRGB_GA + 0.114 * byteRGB_BA);
// Record all pixels of the 3 by 3 matrix into the array.
*(pdobSort + intCount) = dobYUV_YA;
// The count of the 3 by 3 matrix.
intCount++;
} // The closing "The width of the 3 by 3 matrix".
} // The closing "The height of the 3 by 3 matrix".
// Sort the array
for ( int iSortI = 0; iSortI < 9; iSortI++ )
{
// Sort the array
for ( int iSortJ = iSortI; iSortJ < 9; iSortJ++ )
{
double dobA = 0;
double dobB = 0;
// Get a value of index I.
dobA = *(pdobSort + iSortI);
// Get a value of index J.
dobB = *(pdobSort + iSortJ);
// If the value of I more than the value of J, it should exchange.
if ( dobA > dobB )
{
// To exchange them.
*(pdobSort + iSortI) = dobB;
*(pdobSort + iSortJ) = dobA;
}
}
}
// Choose median value from the array.
dobFilterResult = *(pdobSort + 4);
// The index of the image.
lIDXB = ( iX * 3 ) + ( iY * imageB->DibInfo->bmiHeader.biWidth * 3 );
// Set the result of blue into image B.
imageB->DibArry[lIDXB+0] = dobFilterResult;
// Set the result of green into image B.
imageB->DibArry[lIDXB+1] = dobFilterResult;
// Set the result of red into image B.
imageB->DibArry[lIDXB+2] = dobFilterResult;
// Set the result of blue into image A.
imageA->DibArry[lIDXB+0] = dobFilterResult;
// Set the result of green into image A.
imageA->DibArry[lIDXB+1] = dobFilterResult;
// Set the result of red into image A.
imageA->DibArry[lIDXB+2] = dobFilterResult;
} // The closing "The width of the image".
} // The closing "The height of the image".
} // The closing "The loop of median filter".
You can download the source code and binary code.
https://drive.google.com/file/d/0BzHb_OyLyVZlNEprbWtEcFNJQ2s/view?usp=sharing
Exception
There is a notice, if your bit depth of bitmap file are not 24 bits, you should change your bitmap files to adapt this program, or you could rewrite this source code to fit your bitmap format.
You have to install Microsoft SDK v7.1, because I include windowscodes.lib.
#pragma comment(lib, "windowscodecs.lib")
Reference
[1] Gary Bradski and Adrian Kaehler, “Learning OpenCV: Computer Vision with the OpenCV Library,” O’REILLY, September 2008, ISBN:978-0-596-51613-0
Acknowledge
Thank you (Microsoft Visual Studio 2010, Lenna Sjööblom) very much for this great development utility and beautiful photo.
