带矩形OCR的网格字母

Question

我一直试图在图像上用矩形网格化每个字母（在该图像上只有白色和黑色的颜色）。我是这样开始的：

    Dim bmp As Bitmap = Label1.Image
    Dim xmax As Integer
    Dim ymax As Integer
    xmax = Label1.Width - 1
    ymax = Label1.Height - 1
    Dim top, bottom, left, right As Integer
    Dim first As Boolean = True
    Dim last As Boolean = False
    Dim first2 As Boolean = True
    Dim last2 As Boolean = False

    Dim pen As Pen = Pens.Red

    For x = 0 To xmax

        For y = 0 To ymax
            With bmp.GetPixel(x, y)
                If .R = 0 And .G = 0 And .B = 0 And first = True Then
                    left = x 
                    first = False
                    last = True
                ElseIf .R = 0 And .G = 0 And .B = 0 And last = True Then
                    right = x 
                End If
            End With
        Next y
    Next x

    For y = 0 To ymax
        For x = 0 To xmax
            With bmp.GetPixel(x, y)
                If .R = 0 And .G = 0 And .B = 0 And first2 = True Then
                    top = y 
                    first2 = False
                    last2 = True
                ElseIf .R = 0 And .G = 0 And .B = 0 And last2 = True Then
                    bottom = y 
                End If
            End With
        Next x
    Next y
    first = True
    first2 = True
    last = False
    last2 = False
    Dim rect As New Rectangle(left, top, right - left, bottom - top)
    Dim g As Graphics = Graphics.FromImage(bmp)
    g.DrawRectangle(pen, rect)
    Label1.Image = bmp

它会检查图像上的所有像素，它会得到黑色的像素，我只能在一个字母周围绘制矩形，但我当时不能超过一个。 仍然不能将它用于单独的字母。

我会感谢您的所有回复。