C#

Imports Microsoft.VisualBasic

Public Class deskew
    ' Representation of a line in the image.
    Public Class HougLine
        ' Count of points in the line.
        Public Count As Integer
        ' Index in Matrix.
        Public Index As Integer
        ' The line is represented as all x,y that solve y*cos(alpha)-x*sin(alpha)=d
        Public Alpha As Double
        Public d As Double
    End Class
    ' The Bitmap
    Dim cBmp As Bitmap
    ' The range of angles to search for lines
    Const stepsPerDeg = 5
    Const minAngle = -13
    Const maxAngle = 13
    Dim cAlphaStart As Double = minAngle
    Dim cAlphaStep As Double = 1 / stepsPerDeg
    Dim cSteps As Integer = (maxAngle - minAngle) * stepsPerDeg
    ' Precalculation of sin and cos.
    Dim cSinA() As Double
    Dim cCosA() As Double
    ' Range of d
    Dim cDMin As Double
    Dim cDStep As Double = 1
    Dim cDCount As Integer
    ' Count of points that fit in a line.
    Dim cHMatrix() As Integer

    Public getPixelCalls As Long

    Public Sub setAngleRange(ByVal minAngle As Long, ByVal maxAngle As Long)
        cAlphaStart = minAngle
        cSteps = (maxAngle - minAngle) / cAlphaStep
    End Sub

    ' Calculate the skew angle of the image cBmp.
    Public Function GetSkewAngle() As Double
        Dim hl() As deskew.HougLine
        Dim i As Integer
        Dim sum As Double
        Dim count As Integer

        ' Hough Transformation
        Calc()
        ' Top 20 of the detected lines in the image.
        hl = GetTop(20)
        ' Average angle of the lines
        For i = 0 To 19
            sum += hl(i).Alpha
            count += 1
        Next
        Return sum / count
    End Function

    ' Calculate the Count lines in the image with most points.
    Private Function GetTop(ByVal Count As Integer) As HougLine()
        Dim hl() As HougLine
        Dim i As Integer
        Dim j As Integer
        Dim tmp As HougLine
        Dim AlphaIndex As Integer
        Dim dIndex As Integer

        ReDim hl(Count)
        For i = 0 To Count - 1
            hl(i) = New HougLine
        Next
        For i = 0 To cHMatrix.Length - 1
            If cHMatrix(i) > hl(Count - 1).Count Then
                hl(Count - 1).Count = cHMatrix(i)
                hl(Count - 1).Index = i
                j = Count - 1
                While j > 0 AndAlso hl(j).Count > hl(j - 1).Count
                    tmp = hl(j)
                    hl(j) = hl(j - 1)
                    hl(j - 1) = tmp
                    j -= 1
                End While
            End If
        Next
        For i = 0 To Count - 1
            dIndex = hl(i).Index \ cSteps
            AlphaIndex = hl(i).Index - dIndex * cSteps
            hl(i).Alpha = GetAlpha(AlphaIndex)
            hl(i).d = dIndex + cDMin
        Next
        Return hl
    End Function
    Public Sub New(ByVal bmp As Bitmap)
        cBmp = bmp
    End Sub
    ' Hough Transforamtion:
    Private Sub Calc()
        Dim x As Integer
        Dim y As Integer
        Dim hMin As Integer = cBmp.Height / 4
        Dim hMax As Integer = cBmp.Height * 3 / 4

        Init()
        For y = hMin To hMax
            For x = 1 To cBmp.Width - 2
                ' Only lower edges are considered.
                If IsBlack(x, y) Then
                    If Not IsBlack(x, y + 1) Then
                        Calc(x, y)
                    End If
                End If
            Next
        Next
    End Sub
    ' Calculate all lines through the point (x,y).
    Private Sub Calc(ByVal x As Integer, ByVal y As Integer)
        Dim alpha As Integer
        Dim d As Double
        Dim dIndex As Integer
        Dim Index As Integer

        For alpha = 0 To cSteps - 1
            d = y * cCosA(alpha) - x * cSinA(alpha)
            dIndex = CalcDIndex(d)
            Index = dIndex * cSteps + alpha
            Try
                cHMatrix(Index) += 1
            Catch ex As Exception
                Debug.WriteLine(ex.ToString)
            End Try
        Next
    End Sub
    Private Function CalcDIndex(ByVal d As Double) As Double
        Return Convert.ToInt32(d - cDMin)
    End Function
    Private Function IsBlack(ByVal x As Integer, ByVal y As Integer) As Boolean
        Dim c As Color
        Dim luminance As Double
        getPixelCalls += 1
        c = cBmp.GetPixel(x, y)
        luminance = (c.R * 0.299) + (c.G * 0.587) + (c.B * 0.114)
        Return luminance < 140
    End Function
    Private Sub Init()
        Dim i As Integer
        Dim angle As Double
        getPixelCalls = 0
        ' Precalculation of sin and cos.
        ReDim cSinA(cSteps - 1)
        ReDim cCosA(cSteps - 1)
        For i = 0 To cSteps - 1
            angle = GetAlpha(i) * Math.PI / 180.0#
            cSinA(i) = Math.Sin(angle)
            cCosA(i) = Math.Cos(angle)
        Next
        ' Range of d:
        cDMin = -cBmp.Width
        cDCount = 2 * (cBmp.Width + cBmp.Height) / cDStep
        ReDim cHMatrix(cDCount * cSteps)
    End Sub

    Public Function GetAlpha(ByVal Index As Integer) As Double
        Return cAlphaStart + Index * cAlphaStep
    End Function
End Class

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tahernd wrote:

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