Blur and sharpen a bitmap

**Mikro** · 03-13-2005

Latest version of my source.

Code:

	void filter()
	{
		int rsum = 0;
		int gsum = 0;
		int bsum = 0;
		int ksum = 0;
		Pixel p;
		bmp = new Bitmap(bitmap.getHeight(), bitmap.getWidth()); // Dynamically createas an empty Bitmap
		int filter[3][3] = {{0,-1,0}, {-1,5,-1}, {0,-1,0}}; // The sharpen filter

		for (int x = 0; x < bitmap.getHeight(); x++)
		{
			for (int y = 0; y < bitmap.getWidth(); y++)
			{
				for (int row = -1; row < 1; row++)
				{
					for (int col = -1; col < 1; col++)
					{
						if ((x + row) >= 0 && (x + row) < bmp->getHeight())
						{
							if ((y + col) >= 0 && (y + col) < bmp->getWidth())
							{
								p = bitmap.getCopyOfPixel(x, y);
							
								rsum += filter[row + 1][col + 1] * p.r;	// Red
								gsum += filter[row + 1][col + 1] * p.g;	// Green
								bsum += filter[row + 1][col + 1] * p.b;	// Blue
								ksum += filter[row + 1][col + 1];
							}
						}
					}
				}
				
				// To avoid devision by zero
				if (ksum == 0)
				{
					p.r = rsum;
					p.g = gsum;
					p.b = bsum;
				}
				else
				{
					p.r = rsum / ksum;
					p.g = gsum / ksum;
					p.b = bsum / ksum;
				}
		
				// Resets the value
				rsum = 0;	
				gsum = 0;
				bsum = 0;
				ksum = 0;
				bmp->setPixel(x, y, p);  // Inserts the pixel
			}
        }
}

It doesn't matter where I reset the sum values it either goes rubbish or just black. Even tried with different numbers in the matrix filter but still nothing.

**VirtualAce** · 03-13-2005

4 for loops??

Why?

Code:

for (DWORD i=0;i<height;i++)
{
  for (DWORD j=0;j<width;j++)
 {
    DWORD i1=i+1;
    DWORD j1=j+1;

    if (i1>height) i1=0;
    if (j1>width) j1=0;

    WORD avgRed=Buffer[i][j].red+Buffer[i][j1].red+Buffer[i1][j].red+Buffer[i1][j1].red;
    WORD avgGreen=Buffer[i][j].green+Buffer[i][j1].green+Buffer[i1][j].green+Buffer[i1][j1].green;
    WORD avgBlue=Buffer[i][j].blue+Buffer[i][j1].blue+Buffer[i1][j].blue+Buffer[i1][j1].blue;

    avgRed>>=2;
    avgGreen>>=2;
    avgBlue>>=2;

    BlurredBuffer[i][j]=RGB((BYTE)avgRed,(BYTE)avgGreen,(BYTE)avgBlue);
   }
}

The way you are doing it your values will quickly resolve to 0.

I know there are other algorithms for this on google. I searched and found about a billion.

If you are looking for a image manipulation kernel based on matrices there is an easier way. Extract the color values from your bitmap (which is just a big matrix) into a temp matrix the same size as the filter matrix. Concatenate the matrices, write the resulting matrix back into the color buffer or into a blurred buffer. All your values should be normalized so that any muls or divs in your filters won't overflow the data type. With this method you could easily implement any type of matrix filter you want as long as you know how to concatenate the matrices.

**Sang-drax** · 03-13-2005

Bubba, he's trying to implement a sharpen filter.

I think it's too early to optimize the code. 4 for-loops can be good in the beginninng and it allows changing the filter easily.

Mikro your for-loops are wrong:

Code:

for (int row = -1; row <= 1; row++)
{
for (int col = -1; col <= 1; col++)

Code:

p = bitmap.getCopyOfPixel(x + row, y + col);

You need to compare different pixels each time.

Besides, you should compare (x+row) to bitmap.getWidth(), not getHeight().

Change this and try again.

**Mikro** · 03-13-2005

Code:

void filter()
	{
		int rsum = 0;
		int gsum = 0;
		int bsum = 0;
		int ksum = 0;
		Pixel p;
		bmp = new Bitmap(bitmap.getHeight(), bitmap.getWidth()); // Dynamically createas an empty Bitmap
		int filter[3][3] = {{0,-1,0}, {-1,5,-1}, {0,-1,0}}; // The sharpen filter

		for (int x = 0; x < bitmap.getHeight(); x++)
		{
			for (int y = 0; y < bitmap.getWidth(); y++)
			{
				for (int row = -1; row <= 1; row++)
				{
					for (int col = -1; col <= 1; col++)
					{
						if ((x + row) >= 0 && (x + row) < bmp->getHeight())
						{
							if ((y + col) >= 0 && (y + col) < bmp->getWidth())
							{
								p = bitmap.getCopyOfPixel(x + row, y + col);
							
								rsum += filter[row + 1][col + 1] * p.r;	// Red
								gsum += filter[row + 1][col + 1] * p.g;	// Green
								bsum += filter[row + 1][col + 1] * p.b;	// Blue
								ksum += filter[row + 1][col + 1];
							}
						}
					}
				}
				
				// To avoid devision by zero
				if (ksum == 0)
				{
					p.r = rsum;
					p.g = gsum;
					p.b = bsum;
				}
				else
				{
					p.r = rsum / ksum;
					p.g = gsum / ksum;
					p.b = bsum / ksum;
				}
		
				// Resets the value
				rsum = 0;	
				gsum = 0;
				bsum = 0;
				ksum = 0;
				bmp->setPixel(x, y, p);  // Inserts the pixel
			}
        }
}

Well now that I have done the small changes the result now is partly correct. If I try switching getWidth() and getHeight() then slightly more than 50% of the image is displayed. So I am leaving these at the same place for the moment.

**Mikro** · 03-13-2005

Finally it has been solved

Code:

void filter()
	{
		int rsum = 0;
		int gsum = 0;
		int bsum = 0;
		int ksum = 0;
		Pixel p;
		bmp = new Bitmap(bitmap.getHeight(), bitmap.getWidth()); // Dynamically createas an empty Bitmap
		int filter[3][3] = {{0,-1,0}, {-1,5,-1}, {0,-1,0}}; // The sharpen filter

		for (int x = 0; x < bitmap.getHeight(); x++)
		{
			for (int y = 0; y < bitmap.getWidth(); y++)
			{
				for (int row = -1; row <= 1; row++)
				{
					for (int col = -1; col <= 1; col++)
					{
						if ((x + row) >= 0 && (x + row) < bitmap.getHeight())
						{
							if ((y + col) >= 0 && (y + col) < bitmap.getWidth())
							{
								p = bitmap.getCopyOfPixel(x + row, y + col);
							
								rsum += filter[row + 1][col + 1] * p.r;	// Red
								gsum += filter[row + 1][col + 1] * p.g;	// Green
								bsum += filter[row + 1][col + 1] * p.b;	// Blue
								ksum += filter[row + 1][col + 1];
							}
						}
					}
				}
				
				// To avoid devision by zero
				if (ksum == 0)
				{
					p.r = rsum;
					p.g = gsum;
					p.b = bsum;
				}
				else
				{
					if (rsum / ksum > 255)
						p.r = 255;
					else if (rsum / ksum < 0)
						p.r = 0;
					else
						p.r = rsum / ksum;

					if (gsum / ksum > 255)
						p.g = 255;
					else if (gsum / ksum < 0)
						p.g = 0;
					else
						p.g = gsum / ksum;
					if (bsum / ksum > 255)
						p.b = 255;
					else if (bsum / ksum < 0)
						p.b = 0;
					else
						p.b = bsum / ksum;
				}
		
				// Resets the value
				rsum = 0;	
				gsum = 0;
				bsum = 0;
				ksum = 0;
				bmp->setPixel(x, y, p);  // Inserts the pixel
			}
        }
}

I thank everbody that has helped me with this and when I feel that I am done with this program I will post the full source.

**Sang-drax** · 03-13-2005

Originally Posted by Mikro

If I try switching getWidth() and getHeight() then slightly more than 50% of the image is displayed. So I am leaving these at the same place for the moment.

Yes, your code is correct, but you should know that using x for height and y for width is... against common practice.

It got me confused, at least.

Glad that it's finally working.

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