c# - 使用 lockbits 进行图像处理，替代 getpixel？

Question

我正在尝试使用锁位来增加我的图像检测类，但这会导致代码出现问题，因此它无法运行。我如何才能同时使用 lockbits 和 getpixel 以加快图像检测速度，或者有人可以告诉我一个同样快的替代方案吗？

代码:

static IntPtr Iptr = IntPtr.Zero;
    static BitmapData bitmapData = null;
    static public byte[] Pixels { get; set; }
    static public int Depth { get; private set; }
    static public int Width { get; private set; }
    static public int Height { get; private set; }

    static public void LockBits(Bitmap source)

    {
            // Get width and height of bitmap
            Width = source.Width;
            Height = source.Height;

            // get total locked pixels count
            int PixelCount = Width * Height;

            // Create rectangle to lock
            Rectangle rect = new Rectangle(0, 0, Width, Height);

            // get source bitmap pixel format size
            Depth = System.Drawing.Bitmap.GetPixelFormatSize(source.PixelFormat);


            // Lock bitmap and return bitmap data
            bitmapData = source.LockBits(rect, ImageLockMode.ReadWrite,
                                         source.PixelFormat);

            // create byte array to copy pixel values
            int step = Depth / 8;
            Pixels = new byte[PixelCount * step];
            Iptr = bitmapData.Scan0;

            // Copy data from pointer to array
            Marshal.Copy(Iptr, Pixels, 0, Pixels.Length);

    }


     static public bool SimilarColors(int R1, int G1, int B1, int R2, int G2, int B2, int Tolerance)
    {
        bool returnValue = true;
        if (Math.Abs(R1 - R2) > Tolerance || Math.Abs(G1 - G2) > Tolerance || Math.Abs(B1 - B2) > Tolerance)
        {
            returnValue = false;
        }
        return returnValue;
    }


     public bool findImage(Bitmap small, Bitmap large, out Point location)
     {
         unsafe
         {
             LockBits(small);
             LockBits(large);
             //Loop through large images width
             for (int largeX = 0; largeX < large.Width; largeX++)
             {
                 //And height
                 for (int largeY = 0; largeY < large.Height; largeY++)
                 {
                     //Loop through the small width
                     for (int smallX = 0; smallX < small.Width; smallX++)
                     {
                         //And height
                         for (int smallY = 0; smallY < small.Height; smallY++)
                         {
                             //Get current pixels for both image
                             Color currentSmall = small.GetPixel(smallX, smallY);
                             Color currentLarge = large.GetPixel(largeX + smallX, largeY + smallY);
                             //If they dont match (i.e. the image is not there)

                             if (!colorsMatch(currentSmall, currentLarge))
                                 //Goto the next pixel in the large image

                                 goto nextLoop;
                         }
                     }
                     //If all the pixels match up, then return true and change Point location to the top left co-ordinates where it was found
                     location = new Point(largeX, largeY);
                     return true;
                 //Go to next pixel on large image
                 nextLoop:
                     continue;
                 }
             }
             //Return false if image is not found, and set an empty point
             location = Point.Empty;
             return false;
         }
     }

Answer 1

您不会希望依赖 getPixel() 进行图像处理；偶尔调用以获取点值(例如在鼠标悬停时)是可以的，但通常最好在图像内存中或在必要时可以转换为位图的某些 2D 数组中进行图像处理。

首先，您可以尝试编写一个方法，使用 LockBits/UnlockBits 提取一个便于操作的数组。完成对数组的操作后，您可以使用不同的 LockBits/UnlockBits 函数将其写回位图。

这是我过去使用过的一些示例代码。第一个函数从位图中返回值的一维数组。由于您知道位图的宽度，因此可以将此一维数组转换为二维数组以进行进一步处理。完成处理后，您可以调用第二个函数将(修改后的)一维数组再次转换为位图。

public static byte[] Array1DFromBitmap(Bitmap bmp){
    if (bmp == null) throw new NullReferenceException("Bitmap is null");

    Rectangle rect = new Rectangle(0, 0, bmp.Width, bmp.Height);
    BitmapData data = bmp.LockBits(rect, ImageLockMode.ReadWrite, bmp.PixelFormat);
    IntPtr ptr = data.Scan0;

    //declare an array to hold the bytes of the bitmap
    int numBytes = data.Stride * bmp.Height;
    byte[] bytes = new byte[numBytes];

    //copy the RGB values into the array
    System.Runtime.InteropServices.Marshal.Copy(ptr, bytes, 0, numBytes);

    bmp.UnlockBits(data);

    return bytes;           
}

public static Bitmap BitmapFromArray1D(byte[] bytes, int width, int height)
{
    Bitmap grayBmp = new Bitmap(width, height, PixelFormat.Format8bppIndexed);
    Rectangle grayRect = new Rectangle(0, 0, grayBmp.Width, grayBmp.Height);
    BitmapData grayData = grayBmp.LockBits(grayRect, ImageLockMode.ReadWrite, grayBmp.PixelFormat);
    IntPtr grayPtr = grayData.Scan0;

    int grayBytes = grayData.Stride * grayBmp.Height;
    ColorPalette pal = grayBmp.Palette;

    for (int g = 0; g < 256; g++){
        pal.Entries[g] = Color.FromArgb(g, g, g);
    }

    grayBmp.Palette = pal;

    System.Runtime.InteropServices.Marshal.Copy(bytes, 0, grayPtr, grayBytes);

    grayBmp.UnlockBits(grayData);
    return grayBmp;
}

这些方法对 Bitmap 像素格式做出的假设可能不适合您，但我希望总体思路是清楚的:使用 LockBits/UnlockBits 从 Bitmap 中提取字节数组，以便您可以编写和调试算法最很容易，然后再次使用 LockBits/UnlockBits 将数组再次写入位图。

为了可移植性，我建议您的方法返回所需的数据类型，而不是在方法本身内操作全局变量。

如果您一直在使用 getPixel()，那么如上所述转换为数组或从数组转换可以显着加快您的代码速度，只需少量的编码工作投入。