silverlight 图像降噪的研究

手机照相机上自动降噪挺好玩的，于是研究了一下，但具体的算法都没找到。于是自己想了一下，使用平均对比度方法，降低像素颜色的差别。

原理如下：

• 在相片一定范围内计算平均值（修正半径）
• 得出平均值后，对没个像素进行修正（修正强度：0.0到1.0）

假设下图是图像颜色曲线：

通过修正强度值为0.5修正后曲线如下：

这时，图像像素点间对比对会减小，从而实现降噪的效果。

当然，这种方法缺点也比较明显，修正后，相片模糊失真。

主要代码如下：

///
<summary>

///
图像降噪

///
</summary>

///
<param name="srcBmp">原图像</param>

///
<param name="radius">半径</param>

///
<param name="strength">强度</param>

///
<returns></returns>

public
WriteableBitmap ClsNoise(WriteableBitmap srcBmp, int radius, double strength)

{

WriteableBitmap newBitmap = new
WriteableBitmap(srcBmp.PixelWidth, srcBmp.PixelHeight);

Color pixelPercent, pixelSrc;

byte r, g, b;

for (int yRow = 0; yRow < srcBmp.PixelHeight; yRow++)

{

for (int xCol = 0; xCol < srcBmp.PixelWidth; xCol++)

{

pixelSrc = srcBmp.GetPixel(xCol, yRow);

pixelPercent = this.GetPercentileColor(srcBmp, yRow, xCol, radius);

if (pixelSrc == pixelPercent)

{

newBitmap.SetPixel(xCol, yRow, pixelSrc);

}

else

{

r = (byte)(pixelSrc.R + (pixelPercent.R - pixelSrc.R) * strength);

g = (byte)(pixelSrc.G + (pixelPercent.G - pixelSrc.G) * strength);

b = (byte)(pixelSrc.B + (pixelPercent.B - pixelSrc.B) * strength);

newBitmap.SetPixel(xCol, yRow, Color.FromArgb(255, r, g, b));

}

}

}

return newBitmap;

}

///
<summary>

///
获取平均值

///
</summary>

///
<param name="srcBmp"></param>

///
<param name="yRow"></param>

///
<param name="xCol"></param>

///
<param name="radius"></param>

///
<returns></returns>

private
Color GetPercentileColor(WriteableBitmap srcBmp, int yRow, int xCol, int radius)

{

int r = 0, g = 0, b = 0, start_yRow, end_yRow, start_xCol, end_xCol, c = 0;

start_yRow = yRow - radius;

if (start_yRow < 0)

{

start_yRow = 0;

}

end_yRow = yRow + radius;

if (end_yRow > srcBmp.PixelHeight - 1)

{

end_yRow = srcBmp.PixelHeight - 1;

}

start_xCol = xCol - radius;

if (start_xCol < 0)

{

start_xCol = 0;

}

end_xCol = xCol + radius;

if (end_xCol > srcBmp.PixelWidth - 1)

{

end_xCol = srcBmp.PixelWidth - 1;

}

for (int y = start_yRow; y <= end_yRow; y++)

{

for (int x = start_xCol; x <= end_xCol; x++)

{

Color color = srcBmp.GetPixel(x, y);

r += color.R;

b += color.B;

g += color.G;

c++;

}

}

if (c == 0)

{

return srcBmp.GetPixel(xCol, yRow);

}

else

{

return
Color.FromArgb(255, (byte)(r / c), (byte)(g / c), (byte)(b / c));

}

}

如果你用过WriteableBitmap 类，就会发现没有 GetPixel 和 SetPixel 方法的，我是通过扩展方法提供的，如：

public
static
class
WriteableBitmapExtension

{

public
static
Color GetPixel(this
WriteableBitmap bitmap, int xCol, int yRow)

{

byte[] bytes = BitConverter.GetBytes(bitmap.Pixels[bitmap.PixelWidth * yRow + xCol]);

return
Color.FromArgb(bytes[3], bytes[2], bytes[1], bytes[0]);

}

public
static
void SetPixel(this
WriteableBitmap bitmap, int xCol, int yRow, Color color)

{

byte[] bytes = new
byte[] { color.B, color.G, color.R, color.A };

bitmap.Pixels[bitmap.PixelWidth * yRow + xCol] = BitConverter.ToInt32(bytes, 0);

}

}

最终效果如下：