Question

Following function solves the problem, but I don’t understand how to call it, especially “out List ImgLetters” part.

  public static bool ApplyBlobExtractor (Bitmap SourceImg, int LettersCount, out List<Bitmap> ImgLetters)
    {
        ImgLetters = null;
        ImgLetters = new List<Bitmap> ();

        BlobCounter blobCounter  = new BlobCounter ();

        // Sort order
        blobCounter.ObjectsOrder = ObjectsOrder.XY;            
        blobCounter.ProcessImage (SourceImg);
        Blob[] blobs             = blobCounter.GetObjects (SourceImg, false);            

        // Adding images into the image list            
        UnmanagedImage currentImg;            
        foreach (Blob blob in blobs)
        {
            currentImg = blob.Image;
            ImgLetters.Add (currentImg.ToManagedImage ());
        }            

        return ImgLetters.Count == LettersCount;
    }

Now lets look at this:

public static bool ApplyBlobExtractor (Bitmap SourceImg, int LettersCount, out List<Bitmap> ImgLetters)

Bitmap SourceImg – picture, where blobs will be found

int LettersCount – blob that we are going to extract (number)

out List ImgLetters – ???

What does 3rd parameter do (how to call this function)?

Bitmap image1 = new Bitmap(@"C:\1.png");    
..
ApplyBlobExtractor (image1, 1, ??? )
..
image2.save(@"C:\2.png")

Answer 1

an out parameter allows you to get results back from a method call other than through the return parameter. http://msdn.microsoft.com/en-us/library/t3c3bfhx(v=vs.80).aspx

In your example the method ApplyBlobExtractor it appears to take a source Bitmap, and a LetterCount (presumably the number of letters you expect to find) it then uses this Blobcounter object to chop it up. It will return true if it finds the same number of letter you expect to find. It will also provide you the output images as a list back through the out parameter.

to call it would would do something like…

Bitmap img1 = new Bitmap(@"C:\1.png");

List<Bitmap> foundImages;

bool result = ApplyBlobExtractor(img1, 1, out foundImages);