Question

I have a library which contains all font characters (Arial in my case). For example:

I’m using this library to OCR text from image.

The problem is that when you try to OCR such characters as “j”, “/”, “t” – characters could overlap one another! So OCR is now impossible, because characters do not match pattern images (up to 3 pixels are different).

How do I have to deal with this problem? Is there a better way to compare images? (C#, WinForms app)

I’m using this method for comparison:

unsafe public static bool CompareMemCmp(Bitmap b1, Bitmap b2)
    {
        if ((b1 == null) != (b2 == null)) return false;
        if (b1.Size != b2.Size) return false;

        var bd1 = b1.LockBits(new Rectangle(new System.Drawing.Point(0, 0), b1.Size), ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb);
        var bd2 = b2.LockBits(new Rectangle(new System.Drawing.Point(0, 0), b2.Size), ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb);

        try
        {
            IntPtr bd1scan0 = bd1.Scan0;
            IntPtr bd2scan0 = bd2.Scan0;

            int stride = bd1.Stride;
            int len = stride * b1.Height;

            return memcmp(bd1scan0, bd2scan0, len) == 0;
        }
        finally
        {
            b1.UnlockBits(bd1);
            b2.UnlockBits(bd2);
        }
    }

It’s extremely fast and reliable.. but you cant get a result if condition from above is met.. unfortunately.

Answer 1

You could make these character pairs (there could be an unreasonable amount of them though..) “characters” ie. the “-j” combination would be recognized as “-j” character..