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);
        }
    }
}

只有这个示例工作没有问题:

var crop = new Rectangle(0, y, bitmap.Width, h);
var bmp = new Bitmap(bitmap.Width, h);
var tempfile = Application.StartupPath+"\\"+"TEMP"+"\\"+Path.GetRandomFileName();


using (var gr = Graphics.FromImage(bmp))
{
    try
    {
        var dest = new Rectangle(0, 0, bitmap.Width, h);
        gr.DrawImage(image,dest , crop, GraphicsUnit.Point);
        bmp.Save(tempfile,ImageFormat.Jpeg);
        bmp.Dispose();
    }
    catch (Exception)
    {


    }

}

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);
}

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);
        }
    }
}

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

在c#中裁剪图像非常简单。然而，做的东西，你将如何管理裁剪你的图像将会有点困难。

下面的示例是如何在c#中裁剪图像的方法。

var filename = @"c:\personal\images\horizon.png";
var img = Image.FromFile(filename);
var rect = new Rectangle(new Point(0, 0), img.Size);
var cloned = new Bitmap(img).Clone(rect, img.PixelFormat);
var bitmap = new Bitmap(cloned, new Size(50, 50));
cloned.Dispose();