Imports System
Imports System.Drawing
Imports System.Drawing.Imaging
Imports System.Runtime.InteropServices

' Bitmap.LockBits/UnlockBitsの処理をラップしたクラス
Class BitmapLock
  Implements IDisposable

  Private bitmap As Bitmap
  Private data As BitmapData

  Public Sub New(ByVal bitmap As Bitmap, ByVal rect As Rectangle, ByVal mode As ImageLockMode, ByVal format As PixelFormat)
    MyClass.bitmap = bitmap
    MyClass.data = bitmap.LockBits(rect, mode, format)
  End SUb

  Public Sub Dispose() Implements IDisposable.Dispose
    If Not data is Nothing Then
      bitmap.UnlockBits(data)

      data = Nothing
      bitmap = Nothing
    End If
  End Sub

  ' ラインyの先頭のポインタを取得する
  Public Function GetScanLine(ByVal y As Integer) As IntPtr
    If data Is Nothing Then Throw New ObjectDisposedException(Me.GetType().FullName)

    Return New IntPtr(data.Scan0.ToInt32() + y * data.Stride)
  End Function
End Class

Class Sample
  Shared Sub Main()
    Using bitmap As Bitmap = DirectCast(Image.FromFile("origin.png"), Bitmap)
      Dim rect As New Rectangle(0, 0, bitmap.Width, bitmap.Height)

      ' 画像全体のピクセルを読み書きできるようにロックする
      Using locked As New BitmapLock(bitmap, rect, ImageLockMode.ReadWrite, PixelFormat.Format32bppArgb)
        For y As Integer = 0 To rect.Height - 1
          Dim line As IntPtr = locked.GetScanLine(y)

          For x As Integer = 0 To rect.Width - 1
            ' 1ピクセル分読み込み
            Dim col As Integer = Marshal.ReadInt32(line, x * 4)

            ' 反転した値を書き込む
            Marshal.WriteInt32(line, x * 4, Not col)
          Next
        Next
      End Using

      bitmap.Save("negated.png", ImageFormat.Png)
    End Using
  End Sub
End Class