What is the best and fast way to get pixels' column of bitmap?

What is the fastest way to get colu开发者_如何学JAVAmn of pixels from bitmap? I don't consider two loops because it could take to long. I will appreciate for any idea. Thanks!

I would suggest to convert your bitmap into a vector of bytes using the following code:

Bitmpa myImage=new Bitmap("myImage.bmp");    

BitmapData bmpData1=myImage.LockBits(new Rectangle(0,0,myImage.Width,myImage.Height), 
                 System.Drawing.Imaging.ImageLockMode.ReadWrite, myImage.PixelFormat);
byte[] myImageData = new byte[bmpData1.Stride * bmpData1.Height];
System.Runtime.InteropServices.Marshal.Copy(bmpData1.Scan0,myImageData,0
                       ,myImageData.Length);
myImgage.UnlockBits(bmpData1);

Then it becomes easy to retrieve the pixels on the column you want. Just loop through the vector myImageData with a step equals to the number of pixels per rows * the number of bytes per pixel.

Just be careful about the number of bytes per pixel are used for the representation of your bitmap. This depends on the PixelFormat .

Assuming you only need a single column, the following routines should help you.

First here is the standard solution using verifiable C# code

static Color[] GetPixelColumn(Bitmap bmp, int x)
{
  Color[] pixelColumn = new Color[bmp.Height];
  for (int i = 0; i < bmp.Height; ++i)
  {
    pixelColumn[i] = bmp.GetPixel(x, i);
  }
  return pixelColumn;
}

Here is a faster alternative, but this requires that you enable unsafe support for the C# compiler

static Color[] GetPixelColumnFast(Bitmap bmp, int x)
{
  Color[] pixelColumn = new Color[bmp.Height];
  BitmapData pixelData = bmp.LockBits(
    new Rectangle(0, 0, bmp.Width, bmp.Height),
    ImageLockMode.ReadOnly,
    PixelFormat.Format32bppArgb);
  unsafe
  {
    int* pData = (int*)pixelData.Scan0.ToPointer();
    pData += x;
    for (int i = 0; i < bmp.Height; ++i)
    {
      pixelColumn[i] = Color.FromArgb(*pData);
      pData += bmp.Width;
    }
  }
  bmp.UnlockBits(pixelData);

  return pixelColumn;
}

Both functions will return a Color array with the colors of the pixels for a specific column in the bitmap.

Convert it to a array of bytes

    private static byte[, ,] BitmapToBytes(Bitmap bitmap)
    {
        BitmapData bitmapData = 
            bitmap.LockBits(new Rectangle(new Point(), bitmap.Size), ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
        byte[] bitmapBytes;
        var stride = bitmapData.Stride;
        try
        {
            int byteCount = bitmapData.Stride * bitmap.Height;
            bitmapBytes = new byte[byteCount];
            Marshal.Copy(bitmapData.Scan0, bitmapBytes, 0, byteCount);
        }
        finally
        {
            bitmap.UnlockBits(bitmapData);                
        }
        byte[, ,] result = new byte[3, bitmap.Width, bitmap.Height];
        for (int k = 0; k < 3; k++)
        {
            for (int i = 0; i < bitmap.Width; i++)
            {
                for (int j = 0; j < bitmap.Height; j++)
                {
                    result[k, i, j] = bitmapBytes[j * stride + i * 3 + k];
                }
            }
        }
        return result;
    }