How to detect an image border programmatically?

Question

I\'m searching for a program which detects the border of a image, for example I have a square and the program detects the X/Y-Coords

Example:

alt text http://img

Answer 1

This is a very simple edge detector. It is suitable for binary images. It just calculates the differences between horizontal and vertical pixels like image.pos[1,1] = image.pos[1,1] - image.pos[1,2] and the same for vertical differences. Bear in mind that you also need to normalize it in the range of values 0..255.

But! if you just need a program, use Adobe Photoshop.

Code written in C#.

public void SimpleEdgeDetection()
{
    BitmapData data = Util.SetImageToProcess(image);
    if (image.PixelFormat != PixelFormat.Format8bppIndexed)
        return;

    unsafe
    {
        byte* ptr1 = (byte *)data.Scan0;
        byte* ptr2;
        int offset = data.Stride - data.Width;
        int height = data.Height - 1;
        int px;

        for (int y = 0; y < height; y++)
        {
            ptr2 = (byte*)ptr1 + data.Stride;
            for (int x = 0; x < data.Width; x++, ptr1++, ptr2++)
            {
                px = Math.Abs(ptr1[0] - ptr1[1]) + Math.Abs(ptr1[0] - ptr2[0]);
                if (px > Util.MaxGrayLevel) px = Util.MaxGrayLevel;
                ptr1[0] = (byte)px;
            }
            ptr1 += offset;
        }
    }
    image.UnlockBits(data);
}

Method from Util Class

static public BitmapData SetImageToProcess(Bitmap image)
{
    if (image != null)
        return image.LockBits(
            new Rectangle(0, 0, image.Width, image.Height),
            ImageLockMode.ReadWrite,
            image.PixelFormat);

    return null;
}

If you need more explanation or algorithm just ask with more information without being so general.