如何转换像素格式？ C#中从32bppRGB到16bpp灰度

Question

我需要为我的图像做一些阈值处理。 阈值过滤器 function 只接受8-16bpp 灰度。 我的 bitmap 图片具有32bppRGB像素格式。 请建议一些相同的代码。 （我也想知道是否可以不进行逐像素操作）

ps 我正在使用 Aforge.NET 进行阈值处理。

谢谢

-萨加尔

Answer 1

使用 AForge.NET 框架灰度过滤器

过滤器接受 24、32、48 和 64 bpp 彩色图像并产生 8（如果源是 24 或 32 bpp 图像）或 16（如果源是 48 或 64 bpp 图像）bpp 灰度图像。

然后应用阈值过滤器。

Answer 2

最简单的方法：

public static Bitmap MakeGrayscale(Bitmap original)
 {
    //make an empty bitmap the same size as original
    Bitmap newBitmap = new Bitmap(original.Width, original.Height);

   for (int i = 0; i < original.Width; i++)
    {
       for (int j = 0; j < original.Height; j++)
       {
          //get the pixel from the original image
          Color originalColor = original.GetPixel(i, j);

         //create the grayscale version of the pixel
          int grayScale = (int)((originalColor.R * .3) + (originalColor.G * .59)
              + (originalColor.B * .11));

         //create the color object
          Color newColor =  Color.FromArgb(grayScale, grayScale, grayScale);

          //set the new image's pixel to the grayscale version
          newBitmap.SetPixel(i, j, newColor);
         }
     }

    return newBitmap;
 }

更快的方式：

public static Bitmap MakeGrayscale2(Bitmap original)
 {
    unsafe
    {
       //create an empty bitmap the same size as original
       Bitmap newBitmap = new Bitmap(original.Width, original.Height);

      //lock the original bitmap in memory
       BitmapData originalData = original.LockBits(
          new Rectangle(0, 0, original.Width, original.Height),
          ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);

      //lock the new bitmap in memory
       BitmapData newData = newBitmap.LockBits(
          new Rectangle(0, 0, original.Width, original.Height), 
         ImageLockMode.WriteOnly, PixelFormat.Format24bppRgb);

       //set the number of bytes per pixel
       int pixelSize = 3;

      for (int y = 0; y < original.Height; y++)
       {
          //get the data from the original image
          byte* oRow = (byte*)originalData.Scan0 + (y * originalData.Stride);

         //get the data from the new image
          byte* nRow = (byte*)newData.Scan0 + (y * newData.Stride);

         for (int x = 0; x < original.Width; x++)
          {
             //create the grayscale version
             byte grayScale = 
               (byte)((oRow[x * pixelSize] * .11) + //B
                (oRow[x * pixelSize + 1] * .59) +  //G
                (oRow[x * pixelSize + 2] * .3)); //R

            //set the new image's pixel to the grayscale version
             nRow[x * pixelSize] = grayScale; //B
             nRow[x * pixelSize + 1] = grayScale; //G
             nRow[x * pixelSize + 2] = grayScale; //R
          }
       }

      //unlock the bitmaps
       newBitmap.UnlockBits(newData);
       original.UnlockBits(originalData);

      return newBitmap;
    }
 }

最快的方式：

public static Bitmap MakeGrayscale3(Bitmap original)
 {
    //create a blank bitmap the same size as original
    Bitmap newBitmap = new Bitmap(original.Width, original.Height);

    //get a graphics object from the new image
    Graphics g = Graphics.FromImage(newBitmap);

   //create the grayscale ColorMatrix
    ColorMatrix colorMatrix = new ColorMatrix(
       new float[][] 
      {
          new float[] {.3f, .3f, .3f, 0, 0},
          new float[] {.59f, .59f, .59f, 0, 0},
          new float[] {.11f, .11f, .11f, 0, 0},
          new float[] {0, 0, 0, 1, 0},
          new float[] {0, 0, 0, 0, 1}
       });

   //create some image attributes
    ImageAttributes attributes = new ImageAttributes();

   //set the color matrix attribute
    attributes.SetColorMatrix(colorMatrix);

   //draw the original image on the new image
    //using the grayscale color matrix
    g.DrawImage(original, new Rectangle(0, 0, original.Width, original.Height),
       0, 0, original.Width, original.Height, GraphicsUnit.Pixel, attributes);

   //dispose the Graphics object
    g.Dispose();
    return newBitmap;
 }