How to clip a image using 4 corner(x,y) in imagemagick C#

Question

I am using afroge previously to clip image using 4 corners of the image like below and it works fine and only problem with Aforge is not able to handle large images like 40000 X 34000 using bitmap, so I want to check imageMagick to crop using 4 corner, but it seems it accepts x,y and width and height of the image to crop, but this will not work if the image is tilted or not straight.

I have tried ImageMagick using below code, but it takes only one x,y location and height and width, which will provide wrong clipped image

Point location = new Point();
location.X = topleft.X;
location.Y = topleft.Y;        
Size ze = new Size();
ze.Height = width;
ze.Height = height;
Rectangle rt = new Rectangle(location, ze);
MagickGeometry mgeomentory = new MagickGeometry(rt);
originalImage.Crop(mgeomentory);

aforge code - existing code - working perfectly

List<AForge.IntPoint> corners = new List<AForge.IntPoint>();
corners.Add(new AForge.IntPoint(topleft.X, topleft.Y));
corners.Add(new AForge.IntPoint(topright.X, topright.Y));
corners.Add(new AForge.IntPoint(bottomright.X, bottomright.Y));
corners.Add(new AForge.IntPoint(bottomleft.X, bottomleft.Y));

SimpleQuadrilateralTransformation filter = new 
SimpleQuadrilateralTransformation(corners, width, height);
Bitmap newImage = filter.Apply(originalImage);

Answer 1

I've rewritten jcupitt's example code in C#. This example uses net-vips, the C# binding for libvips.

static void Main(string[] args)
{
    if (args.Length != 8)
    {
        Console.WriteLine(
            "Usage: [input] [output] " +
            "[topLeftX] [topLeftY] " +
            "[topRightX] [topRightY] " +
            "[bottomRightX] [bottomRightY]");
        return;
    }

    Image image = Image.NewFromFile(args[0]);
    string outFilename = args[1];
    int topLeftX = int.Parse(args[2]);
    int topLeftY = int.Parse(args[3]);
    int topRightX = int.Parse(args[4]);
    int topRightY = int.Parse(args[5]);
    int bottomRightX = int.Parse(args[6]);
    int bottomRightY = int.Parse(args[7]);

    // the angle the top edge is rotated by
    int dx = topRightX - topLeftX;
    int dy = topRightY - topLeftY;
    double angle = (180 / Math.PI) * Math.Atan2(dx, dy);
    if (angle < -45 || angle >= 45)
    {
        angle = 90 - angle;
    }

    // therefore the angle to rotate by to get it straight
    angle = -angle;

    image = image.Rotate(angle);

    // the new position of the rectangle in the rotated image
    double radians = (Math.PI * angle) / 180.0;
    double c = Math.Cos(radians);
    double s = Math.Sin(radians);

    int left = Convert.ToInt32(topLeftX * c - topLeftY * s);
    int top = Convert.ToInt32(topLeftX * s + topLeftY * c);
    int width = Convert.ToInt32(Math.Sqrt(Math.Pow(topRightX - topLeftX, 2) +
                                          Math.Pow(topRightY - topLeftY, 2)));
    int height = Convert.ToInt32(Math.Sqrt(Math.Pow(topRightX - bottomRightX, 2) +
                                           Math.Pow(topRightY - bottomRightY, 2)));

    // after a rotate, the new position of the origin is given by .Xoffset, .Yoffset
    Image tile = image.Crop(left + image.Xoffset, top + image.Yoffset, width, height);

    tile.WriteToFile(outFilename);
}

Note that if you need OpenSlide support on Windows, you'll have to use the libvips -all distribution. For security reasons, NetVips only bundles the -web libvips x86/x64 distribution. See here for a complete tutorial.