对于任何愿意使用“不安全”代码的人来说，您可以获得比标准System.Drawing.Graphics方法更好的性能，如果使用Bitmap.Clone()则更好。

请记住，32bpp是该方法支持的唯一格式。(其他格式可以工作，只要1像素存储为4字节)

我包含了两个版本，一个使用Span，它在裁剪到较小的图像时性能稍好。 如果裁剪到1000x1000的图像，它们的速度差不多。

如果感兴趣，基准在下面。

public static class BitmapExtension
{
    unsafe public static Bitmap Crop(this Bitmap bitmap, int left, int top, int width, int height)
    {
        Bitmap cropped = new Bitmap(width, height);
        BitmapData originalData = bitmap.LockBits(new System.Drawing.Rectangle(0, 0, bitmap.Width, bitmap.Height), ImageLockMode.ReadOnly, bitmap.PixelFormat);
        BitmapData croppedData = cropped.LockBits(new System.Drawing.Rectangle(0, 0, width, height), ImageLockMode.WriteOnly, bitmap.PixelFormat);

        int* srcPixel = (int*)originalData.Scan0 + (left + originalData.Width * top);
        int nextLine = originalData.Width - width;

        for (int y = 0, i = 0; y < height; y++, srcPixel += nextLine)
        {
            for (int x = 0; x < width; x++, i++, srcPixel++)
            {
                *((int*)croppedData.Scan0 + i) = *srcPixel;
            }
        }

        bitmap.UnlockBits(originalData);
        cropped.UnlockBits(croppedData);

        return cropped;
    }

    unsafe public static Bitmap CropSmall(this Bitmap bitmap, int left, int top, int width, int height)
    {
        Bitmap cropped = new Bitmap(width, height);
        BitmapData originalData = bitmap.LockBits(new System.Drawing.Rectangle(0, 0, bitmap.Width, bitmap.Height), ImageLockMode.ReadOnly, bitmap.PixelFormat);
        BitmapData croppedData = cropped.LockBits(new System.Drawing.Rectangle(0, 0, width, height), ImageLockMode.WriteOnly, bitmap.PixelFormat);

        Span<int> srcPixels = new Span<int>((void*)originalData.Scan0, originalData.Width * originalData.Height);

        int nextLine = originalData.Width - width;

        for (int y = 0, i = 0, s = left + originalData.Width * top; y < height; y++, s += nextLine)
        {
            for (int x = 0; x < width; x++, i++, s++)
            {
                *((int*)croppedData.Scan0 + i) = srcPixels[s];
            }
        }

        bitmap.UnlockBits(originalData);
        cropped.UnlockBits(croppedData);

        return cropped;
    }
}

裁剪3440x1440到1000x1000

裁剪3440x1440到256x256

裁剪3440x1440到1440x1440

查看这个链接:http://www.switchonthecode.com/tutorials/csharp-tutorial-image-editing-saving-cropping-and-resizing

private static Image cropImage(Image img, Rectangle cropArea)
{
   Bitmap bmpImage = new Bitmap(img);
   return bmpImage.Clone(cropArea, bmpImage.PixelFormat);
}

对于任何愿意使用“不安全”代码的人来说，您可以获得比标准System.Drawing.Graphics方法更好的性能，如果使用Bitmap.Clone()则更好。

请记住，32bpp是该方法支持的唯一格式。(其他格式可以工作，只要1像素存储为4字节)

我包含了两个版本，一个使用Span，它在裁剪到较小的图像时性能稍好。 如果裁剪到1000x1000的图像，它们的速度差不多。

如果感兴趣，基准在下面。

public static class BitmapExtension
{
    unsafe public static Bitmap Crop(this Bitmap bitmap, int left, int top, int width, int height)
    {
        Bitmap cropped = new Bitmap(width, height);
        BitmapData originalData = bitmap.LockBits(new System.Drawing.Rectangle(0, 0, bitmap.Width, bitmap.Height), ImageLockMode.ReadOnly, bitmap.PixelFormat);
        BitmapData croppedData = cropped.LockBits(new System.Drawing.Rectangle(0, 0, width, height), ImageLockMode.WriteOnly, bitmap.PixelFormat);

        int* srcPixel = (int*)originalData.Scan0 + (left + originalData.Width * top);
        int nextLine = originalData.Width - width;

        for (int y = 0, i = 0; y < height; y++, srcPixel += nextLine)
        {
            for (int x = 0; x < width; x++, i++, srcPixel++)
            {
                *((int*)croppedData.Scan0 + i) = *srcPixel;
            }
        }

        bitmap.UnlockBits(originalData);
        cropped.UnlockBits(croppedData);

        return cropped;
    }

    unsafe public static Bitmap CropSmall(this Bitmap bitmap, int left, int top, int width, int height)
    {
        Bitmap cropped = new Bitmap(width, height);
        BitmapData originalData = bitmap.LockBits(new System.Drawing.Rectangle(0, 0, bitmap.Width, bitmap.Height), ImageLockMode.ReadOnly, bitmap.PixelFormat);
        BitmapData croppedData = cropped.LockBits(new System.Drawing.Rectangle(0, 0, width, height), ImageLockMode.WriteOnly, bitmap.PixelFormat);

        Span<int> srcPixels = new Span<int>((void*)originalData.Scan0, originalData.Width * originalData.Height);

        int nextLine = originalData.Width - width;

        for (int y = 0, i = 0, s = left + originalData.Width * top; y < height; y++, s += nextLine)
        {
            for (int x = 0; x < width; x++, i++, s++)
            {
                *((int*)croppedData.Scan0 + i) = srcPixels[s];
            }
        }

        bitmap.UnlockBits(originalData);
        cropped.UnlockBits(croppedData);

        return cropped;
    }
}

裁剪3440x1440到1000x1000

裁剪3440x1440到256x256

裁剪3440x1440到1440x1440

你可以使用[图形。使用DrawImage][1]将裁剪图像从位图绘制到图形对象上。

Rectangle cropRect = new Rectangle(...);
using (Bitmap src = Image.FromFile("") as Bitmap)
{
    using (Bitmap target = new Bitmap(cropRect.Width, cropRect.Height))
    {
        using (Graphics g = Graphics.FromImage(target))
        {
            g.DrawImage(src, new Rectangle(0, 0, target.Width, target.Height),
                cropRect,
                GraphicsUnit.Pixel);
        }
    }
}

我正在寻找一个简单和快速的函数，没有额外的库来做这项工作。我尝试了尼克斯解决方案，但我需要29.4秒来“提取”一个atlas文件的1195张图像。所以后来我用这种方法做了同样的工作，需要2.43秒。也许这个会有帮助。

// content of the Texture class
public class Texture
{
    //name of the texture
    public string name { get; set; }
    //x position of the texture in the atlas image
    public int x { get; set; }
    //y position of the texture in the atlas image
    public int y { get; set; }
    //width of the texture in the atlas image
    public int width { get; set; }
    //height of the texture in the atlas image
    public int height { get; set; }
}

Bitmap atlasImage = new Bitmap(@"C:\somepicture.png");
PixelFormat pixelFormat = atlasImage.PixelFormat;

foreach (Texture t in textureList)
{
     try
     {
           CroppedImage = new Bitmap(t.width, t.height, pixelFormat);
           // copy pixels over to avoid antialiasing or any other side effects of drawing
           // the subimages to the output image using Graphics
           for (int x = 0; x < t.width; x++)
               for (int y = 0; y < t.height; y++)
                   CroppedImage.SetPixel(x, y, atlasImage.GetPixel(t.x + x, t.y + y));
           CroppedImage.Save(Path.Combine(workingFolder, t.name + ".png"), ImageFormat.Png);
     }
     catch (Exception ex)
     {
          // handle the exception
     }
}

这很简单:

创建一个裁剪大小的新位图对象。 使用图形。为新的位图创建一个图形对象。 使用DrawImage方法将图像绘制到具有负X和负Y坐标的位图上。