問題描述

我一直在尋找將位圖轉換為 8bpp 的最快方法.我找到了兩種方法:

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. 結果質量非常低(托盤不良)

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

和 2 給了我一個負步幅的位圖，當我嘗試鎖定位并將數據復制到字節數組時，我得到一個異常:嘗試讀取或寫入受保護的內存.這通常表明其他內存已損壞.

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);

我怎樣才能讓 2 取得積極的進展?或者如何使用負步幅的鎖位復制數據?

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

推薦答案

一次復制 1 行，計算一行的起始指針為 ((byte*)scan0 + (y * stride)).無論是正步幅還是負步幅，代碼都是相同的.