c#-使用安全代码将频道从一个图像复制到另一个

我试图使用System.Runtime.InteropServices.Marshal.Copy重构此不安全的代码,以将单个ARGB通道从一个图像复制到另一个图像,如本例中MSDN所示,但我完全迷失了.

谁能指导我完成我的工作？

public enum ChannelARGB
{
    Blue = 0,
    Green = 1,
    Red = 2,
    Alpha = 3
}

public static void transferOneARGBChannelFromOneBitmapToAnother(
    Bitmap source,
    Bitmap dest,
    ChannelARGB sourceChannel,
    ChannelARGB destChannel )
{
    if ( source.Size!=dest.Size )
        throw new ArgumentException();
    Rectangle r = new Rectangle( Point.Empty, source.Size );
    BitmapData bdSrc = source.LockBits( r, 
                                        ImageLockMode.ReadOnly, 
                                        PixelFormat.Format32bppArgb );
    BitmapData bdDst = dest.LockBits( r, 
                                      ImageLockMode.ReadWrite,
                                      PixelFormat.Format32bppArgb );
    unsafe
    {
        byte* bpSrc = (byte*)bdSrc.Scan0.ToPointer();
        byte* bpDst = (byte*)bdDst.Scan0.ToPointer();
        bpSrc += (int)sourceChannel;
        bpDst += (int)destChannel;
        for ( int i = r.Height * r.Width; i > 0; i-- )
        {
            *bpDst = *bpSrc;
            bpSrc += 4;
            bpDst += 4;
        }
    }
    source.UnlockBits( bdSrc );
    dest.UnlockBits( bdDst );
}

编辑

为了尝试通过@Ben Voigt walk,尽管到目前为止我已经提出了这个建议.不幸的是,我现在收到以下错误：

Attempted to read or write protected memory. This is often an
indication that other memory is corrupt.

    private static void TransferOneArgbChannelFromOneBitmapToAnother(
                                         Bitmap source,
                                         Bitmap destination, 
                                         ChannelARGB sourceChannel, 
                                         ChannelARGB destinationChannel)
    {
        if (source.Size != destination.Size)
        {
            throw new ArgumentException();
        }

        Rectangle rectangle = new Rectangle(Point.Empty, source.Size);

        // Lockbits the source.
        BitmapData bitmapDataSource = source.LockBits(rectangle,
                                                  ImageLockMode.ReadWrite,
                                                  PixelFormat.Format32bppArgb);

        // Declare an array to hold the bytes of the bitmap.
        int bytes = bitmapDataSource.Stride * bitmapDataSource.Height;

        // Allocate a buffer for the source image
        byte[] sourceRgbValues = new byte[bytes];

        // Get the address of the first line.
        IntPtr ptrSource = bitmapDataSource.Scan0;

        // Copy the RGB values into the array.
        System.Runtime.InteropServices.Marshal.Copy(ptrSource, 
                                                    sourceRgbValues, 
                                                    0, 
                                                    bytes);

        // Unlockbits the source.
        source.UnlockBits(bitmapDataSource);

        // Lockbits the destination.
        BitmapData bitmapDataDestination = destination.LockBits(rectangle,
                                                  ImageLockMode.ReadWrite,
                                                  PixelFormat.Format32bppArgb);

        // Allocate a buffer for image
        byte[] destinationRgbValues = new byte[bytes];

        IntPtr ptrDestination = bitmapDataDestination.Scan0;

        // Copy the RGB values into the array.
        System.Runtime.InteropServices.Marshal.Copy(ptrDestination,
                                                    destinationRgbValues, 
                                                    0, 
                                                    bytes);

        ptrSource += (int)sourceChannel;
        ptrDestination += (int)destinationChannel;

        for (int i = rectangle.Height * rectangle.Width; i > 0; i--)
        {
            destinationRgbValues[i] = sourceRgbValues[i];
            ptrSource += 4;
            ptrDestination += 4;
        }

        // Copy the RGB values back to the bitmap
        // ******This is where I am getting the exception*******.
        System.Runtime.InteropServices.Marshal.Copy(destinationRgbValues, 
                                                    0, 
                                                    ptrDestination, 
                                                    bytes);

        // Unlock bits the destination.
        destination.UnlockBits(bitmapDataDestination);
    }

谁能看到我做错了吗？老实说,这有点让我烦恼.我想我应该买一些书.

解决方法:

> LockBits源.
>元帅.将源BitmapData复制到byte []缓冲区.
>解锁源.
> LockBits目的地.
>元帅.将目标BitmapData复制到byte []缓冲区.
>遍历并将该通道从源字节[]复制到目标字节[](请注意,对索引而不是对指针使用算术运算)
>元帅.将目标字节[]复制回BitmapData.
>解锁目标.

不过,我不确定这是什么意思.使用Marshal.Copy的代码与使用unsafe关键字的代码一样危险,并且应该需要类似的代码安全权限.

可能更有效的方法是使用ImageAttributes.SetColorMatrix从目标图像中删除所需的通道,从源图像中删除所有其他通道,然后进行融合.参见示例ColorMatrix

或者使用DirectX(或OpenGL)和仅传输一个通道的着色器.

标签：gdi-2,c
来源： https://codeday.me/bug/20191201/2079271.html