In VB.NET, how do I save a bitmap in a pixel-indexed format?

[CMousseau]

Ladies and Gentlemen,

 

I am presently developing an application that will watermark .TIFF images we have on our system. These images are strictly black-and-white, so they are stored in 1 bit-per-pixel indexed format (Imaging.PixelFormat.Format1bppindexed) which naturally leads to them being very compressed.

 

Now, I know that you cannot assign a Graphics object to an indexed-pixel image, so I create a mediary bitmap in Imaging.PixelFormat.Format24bppRGB and use the first bitmap as a source to draw into the second one, to wit:

 

' Read source TIFF into new bitmap object

Dim m_clsSource As New Bitmap(strPath)

 

' Create destination bitmap object with the same features

Dim m_clsDest As New Bitmap(m_clsSource.Width, m_clsSource.Height, Imaging.PixelFormat.Format24bppRgb)

m_clsDest.SetResolution(m_clsSource.HorizontalResolution, m_clsSource.VerticalResolution)

 

Dim m_clsFrame As Bitmap

Dim m_clsCanvas As Graphics = Graphics.FromImage(m_clsDest)

 

Dim X, intPageCount As Integer

intPageCount = m_clsSource.GetFrameCount(Imaging.FrameDimension.Page)

 

m_clsCanvas.DrawImage(m_clsSource, 0, 0, m_clsDest.Width, m_clsDest.Height)

 

My question is, now - how do I go about converting m_clsDest back into the 1 bit-per-pixel indexed format?

 

Or, is there a graphics tool/class available on the net that would enable me to directly manipulate the graphic in its native 1bpp mode? Note that my employer's security policy would dictate that I need the source code for such a class and compile it personally.

 

Thank you for your time,

Charles Mousseau.

 

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