C# 如何将我的 getPixel/SetPixel 颜色处理转换为 Lockbits？

Question

编辑:非常感谢您的回复。我在这里最需要的是示例代码，用于说明我对嵌套循环中的几行代码所做的工作，因为这在 GetPixel/SetPixel 中是有效的，但也是我无法使用 Lockbits 正确工作的。谢谢

我正在尝试将我的图像处理过滤器从 GetPixel/SetPixel 转换为 Lockbits，以缩短处理时间。 我也在 Stack Overflow、MSDN 和其他网站上看到了 Lockbits 教程，但我做错了。我从一个非常简单的过滤器开始，它只是减少绿色以创建一个红色和紫色效果。这是我的代码:

   private void redsAndPurplesToolStripMenuItem_Click(object sender, EventArgs e)
    {
        // Get bitmap from picturebox
        Bitmap bmpMain = (Bitmap)pictureBoxMain.Image.Clone();

        // search through each pixel via x, y coordinates, examine and make changes. Dont let values exceed 255 or fall under 0.  
        for (int y = 0; y < bmpMain.Height; y++)
            for (int x = 0; x < bmpMain.Width; x++)
            {
                bmpMain.GetPixel(x, y);
                Color c = bmpMain.GetPixel(x, y);
                int myRed = c.R, myGreen = c.G, myBlue = c.B;
                myGreen -= 128;
                if (myGreen < 0) myGreen = 0; 
                bmpMain.SetPixel(x, y, Color.FromArgb(255, myRed, myGreen, myBlue));
            }

        // assign the new bitmap to the picturebox
        pictureBoxMain.Image = (Bitmap)bmpMain;

        // Save a copy to the HD for undo / redo.
        string myString = Environment.GetEnvironmentVariable("temp", EnvironmentVariableTarget.Machine);
        pictureBoxMain.Image.Save(myString + "\\ColorAppRedo.png", System.Drawing.Imaging.ImageFormat.Png);
    }

因此 GetPixel/SetPixel 代码可以正常工作，但速度很慢。所以我试了一下:

    private void redsAndPurplesToolStripMenuItem_Click(object sender, EventArgs e)
    {
        // Get bitmap from picturebox
        Bitmap bmpMain = (Bitmap)pictureBoxMain.Image.Clone();

        Rectangle rect = new Rectangle(Point.Empty, bmpMain.Size); 
        BitmapData bmpData = bmpMain.LockBits(rect, ImageLockMode.ReadOnly, bmpMain.PixelFormat); 

        // search through each pixel via x, y coordinates, examine and make changes. Dont let values exceed 255 or fall under 0.  
        for (int y = 0; y < bmpMain.Height; y++)
            for (int x = 0; x < bmpMain.Width; x++)
            {
                bmpMain.GetPixel(x, y);
                Color c = new Color(); 
                int myRed = c.R, myGreen = c.G, myBlue = c.B;
                myGreen -= 128;
                if (myGreen < 0) myGreen = 0; 
                bmpMain.SetPixel(x, y, Color.FromArgb(255, myRed, myGreen, myBlue));

            }

        bmpMain.UnlockBits(bmpData); 

        // assign the new bitmap to the picturebox
        pictureBoxMain.Image = (Bitmap)bmpMain;

        // Save a copy to the HD for undo / redo.
        string myString = Environment.GetEnvironmentVariable("temp", EnvironmentVariableTarget.Machine);
        pictureBoxMain.Image.Save(myString + "\\ColorAppRedo.png", System.Drawing.Imaging.ImageFormat.Png);
    } 

当它到达嵌套的第一行时抛出错误“System.Drawing.dll 附加信息中发生类型为‘System.InvalidOperationException’的未处理异常:位图区域已被锁定”环形。

我意识到这一定是初学者的错误，如果有人可以演示将这个非常简单的过滤器转换为 Lockbits 的正确方法，我将不胜感激。非常感谢

Answer 1

scan0 返回的数组是这种格式 BGRA BGRA BGRA BGRA ...等等，其中 B = 蓝色，G = 绿色，R = 红色，A = Alpha。

4 像素宽和 3 像素高的非常小的位图示例。

BGRA BGRA BGRA BGRA
BGRA BGRA BGRA BGRA
BGRA BGRA BGRA BGRA 

stride = width*bytesPerPixel = 4*4 = 16 bytes
height = 3
maxLenght = stride*height= 16*3 = 48 bytes

要达到图像中的某个像素 (x, y) 使用此公式

int certainPixel = bytesPerPixel*x + stride * y;
B = scan0[certainPixel + 0];
G = scan0[certainPixel + 1];
R = scan0[certainPixel + 2];
A = scan0[certainPixel + 3];

---

    public unsafe void Test(Bitmap bmp)
    {
        int width = bmp.Width;
        int height = bmp.Height;
        //TODO determine bytes per pixel
        int bytesPerPixel = 4; // we assume that image is Format32bppArgb
        int maxPointerLenght = width * height * bytesPerPixel;
        int stride = width * bytesPerPixel;
        byte R, G, B, A;

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


        byte* scan0 = (byte*)bData.Scan0.ToPointer();

        for (int i = 0; i < maxPointerLenght; i += 4)
        {
            B = scan0[i + 0];
            G = scan0[i + 1];
            R = scan0[i + 2];
            A = scan0[i + 3];

            // do anything with the colors
            // Set the green component to 0
            G = 0;
            // do something with red
            R = R < 54 ? (byte)(R + 127) : R;
            R = R > 255 ? 255 : R;
        }


        bmp.UnlockBits(bData);
    }

你可以测试的是你自己。在画图或任何其他程序中创建一个非常小的位图(几个像素的宽度/高度)，并在该方法的开头放置一个断点。