如何从负步幅位图复制的像素数据？ [英] How can I copy the pixel data from a Bitmap with negative stride?

问题描述

我一直在寻找一个位图转换为8bpp的最快方法。
我发现2种方式：

I was looking for the fastest way to convert a Bitmap to 8bpp. I found 2 ways:

1

        public static System.Drawing.Image ConvertTo8bpp(Bitmap oldbmp)
    {
        using (var ms = new MemoryStream())
        {
            oldbmp.Save(ms, ImageFormat.Gif);
            ms.Position = 0;
            return System.Drawing.Image.FromStream(ms);
        }
    }

2 http://www.wischik.com /lu/programmer/1bpp.html

但是：
1 在一个非常低质量的结果，结果（坏托盘）

But: 1. Results in a very low quality result (bad pallet)

和 2 给我负步幅位图，当我尝试lockbits和数据复制到一个字节数组我得到一个异常：尝试读取或写入受保护的内存。这通常是指示其他内存已损坏。的

and 2 gives me a Bitmap with negative stride, when I try to lockbits and copy the data to a byte array I get an exception: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.

        BitmapData bmpData = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height), ImageLockMode.ReadWrite, bmp.PixelFormat);

        this.stride = bmpData.Stride;
        this.bytesPerPixel = GetBytesPerPixel(bmp.PixelFormat);
        int length = bmpData.Stride * bmp.Height;
        if (this.stride < 0)
            this.data = new byte[-length];
        else
            this.data = new byte[length];
        Marshal.Copy(bmpData.Scan0, data, 0, length);

        //Unlock the bitmap
        bmp.UnlockBits(bmpData);

我怎样才能让 2 给出了肯定的步伐？或者我如何可以复制使用负箭步lockbits数据??

How can I make 2 gives a positive stride? Or how can I copy data using lockbits of a negative stride??

推荐答案

复制1个排的时间，​​计算行的起始指针（（BYTE *）SCAN0 +（Y *步幅） ）。的code将是正或负的步幅相同。

Copy 1 row at a time, calculating the starting pointer for a row as ((byte*)scan0 + (y * stride)). The code will be identical for either positive or negative stride.

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