利用asp.net怎么改变改变网页中图片的颜色

#region 改变图片颜色 

/// <summary> 
/// 改变图片的颜色 
/// </summary> 
/// <param name="filePath">图片的完整路径</param> 
/// <param name="colorIndex">改变的颜色，true为灰色，false为彩色</param> 
public void update_pixelColor(string filePath, bool colorIndex) 
{ 
Bitmap bmp = new Bitmap(Bitmap.FromFile(filePath)); 

int value = 0; 

for (int i = 0; i < bmp.Height; i++) 
{ 
for (int j = 0; j < bmp.Width; j++) 
{ 
if (colorIndex) 
value = this.GetGrayNumColor(bmp.GetPixel(j, i)); 
else 
value = this.GetHongNumColor(bmp.GetPixel(j, i)); 

bmp.SetPixel(j, i, Color.FromArgb(value, value, value)); 
} 
} 

bmp.Save(filePath); 
} 

/// <summary> 
/// 获取彩色单点像素 
/// </summary> 
/// <param name="posClr">单点像素</param> 
/// <returns>int</returns> 
private int GetHongNumColor(Color posClr) 
{ 
return (posClr.R * 19595 + posClr.G * 38469 + posClr.B * 7472) >> 16; 
} 

/// <summary> 
/// 获取灰色单点像素 
/// </summary> 
/// <param name="posClr">单点像素</param> 
/// <returns>Color</returns> 
private int GetGrayNumColor(Color posClr) 
{ 
//要改变ARGB 
return (posClr.R * 19595 + posClr.G * 38469 + posClr.B * 7472) >> 16; 
} 

#endregion 改变图片颜色