How to "Threshold" and "Histogram Equalize" an image?

  ' Threshold
  Dim threshold As Byte
  threshold = 250

  ' Load source bitmap
  Dim bitmap As New GraphicsMill.bitmap
  bitmap.LoadFromFile "c:\c1rr-aurigma.jpg"
  
  ' Convert bitmap to grayscale
  bitmap.Data.ConvertTo8bppGrayscale
  
  ' Apply threshold using low-level access to bitmap
  bitmap.LockData
  Dim arrSrcRow() As Byte
  Dim I As Long
  Dim J As Long
  Dim ptrSrcRow As Long
  
  ReDim arrSrcRow(0 To bitmap.Data.Stride - 1)
  ptrSrcRow = VarPtr(arrSrcRow(0))
    
  For J = 0 To bitmap.Data.Height - 1
     CopyMemory ByVal ptrSrcRow, ByVal bitmap.Data.Scan0 + J * bitmap.Data.Stride, bitmap.Data.Stride
     For I = 0 To bitmap.Data.Width - 1
       If arrSrcRow(I) < threshold Then
          arrSrcRow(I) = 0
       End If
    Next
    CopyMemory ByVal bitmap.Data.Scan0 + J * bitmap.Data.Stride, ByVal ptrSrcRow, bitmap.Data.Stride
  Next
  bitmap.UnlockData
  
  ' Prepare destination image
  bitmap.ColorAdjustment.Invert
  bitmap.Effects.MinimumFilter 1
  bitmap.Data.ConvertTo1bppIndexed
  
  ' Save destination image
  bitmap.SaveToFile "c:\1.png"