Public Class Form1
    Inherits System.Windows.Forms.Form
 
#Region " Windows Form Designer generated code "
 
    Private Ramp1(255, 2) As Short
    Private Ramp2(255, 2) As Short
    Dim a As Short, b As Short
    Dim varAbdunkeln As Boolean
    Dim varStart As Boolean
    Private Declare Function GetDeviceGammaRamp Lib "gdi32" (ByVal hdc As _
      IntPtr, ByRef lpv As Short) As Integer
    Private Declare Function SetDeviceGammaRamp Lib "gdi32" (ByVal hdc As _
    IntPtr, ByRef lpv As Short) As Integer
 
    Public Sub GammaAbdunkeln()
        Dim g As Graphics = Me.CreateGraphics
        Dim varHDC As IntPtr
        Try
            varHDC = g.GetHdc
            SetDeviceGammaRamp(varHDC, Ramp1(0, 0))
            varAbdunkeln = False
        Catch eX As System.Exception
            MsgBox("Abdunkeln" & eX.ToString())
        Finally
            g.ReleaseHdc(varHDC)
            g.Dispose()
        End Try
    End Sub
 
    Public Sub GammaAufhellen()
        Dim g As Graphics = Me.CreateGraphics
        Dim varHDC As IntPtr
        Try
            varHDC = g.GetHdc
            'On Error Resume Next
            Dim iCtr As Short
            Dim lVal As Long
 
            For iCtr = 0 To 255
                lVal = Ramp1(iCtr, 0)
                Ramp2(iCtr, 0) = Ramp1(iCtr, 0) / b
                Ramp2(iCtr, 1) = Ramp1(iCtr, 1) / b
                Ramp2(iCtr, 2) = Ramp1(iCtr, 2) / b
            Next iCtr
 
            a = a - 2
            SetDeviceGammaRamp(varHDC, Ramp2(0, 0))
            varAbdunkeln = True
        Catch eX As System.Exception
            MsgBox("Aufhellen" & eX.ToString())
        Finally
            g.ReleaseHdc(varHDC)
            g.Dispose()
        End Try
    End Sub
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles MyBase.Load
        Dim g As Graphics = Me.CreateGraphics
        Dim varHDC As IntPtr
        Try
            varHDC = g.GetHdc
            If Not varStart = True Then
                GetDeviceGammaRamp(varHDC, Ramp1(0, 0))
                a = 2
                b = 2
                varStart = True
            End If
        Catch eX As System.Exception
            MsgBox("Laden" & eX.ToString())
        Finally
            g.ReleaseHdc(varHDC)
            g.Dispose()
        End Try
 
    End Sub
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button1.Click
        If Not varAbdunkeln = True Then
            GammaAufhellen()
        Else
            GammaAbdunkeln()
        End If
    End Sub
 
End Class

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