Merge large monochromatic (BW) images

Question

I need to work with large monochromatic images. I basically need to add a banner (frame and formatted text) to a hi-res (like 30000x20000px) monochromatic images (A2+ plots at 400dpi).

The default PixelFormat is Format1bppIndexed, which makes even those large picture relatively small in size. However, using .NET GDI+ Graphics object requires unindexed bitmap.

When turning the image to lowest available unindexed PixelFormat.Format16bppGrayscale:

bmpResized = ImgResized.Clone(New System.Drawing.Rectangle(0, 0, ImgResized.Width, ImgResized.Height),
             System.Drawing.Imaging.PixelFormat.Format16bppGrayScale)

...it becomes to large to be handled by Image and Bitmap (OutOfMemoryExeption: Not enough memory - on 32GB machine). I tried to create the banner separately and join the pictures pixel-wise, however I ran into the very same limitations - SetPixel requires unindexed bitmap.

Is there any way to overcome those issues?

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EDIT: A possible solution would be to create a byte array and edit the bytes as per [https://social.msdn.microsoft.com/Forums/vstudio/en-US/54a096ff-46f3-45ce-8560-bf5a0618ef75/how-to-set-pixel-into-bitmap-with-pixel-format-of-format8bppindexed-?forum=csharpgeneral][1]. However I'm not sure how exactly I can "shift" the 2nd image byte-wise.

Answer 1

Finally I had to do it using bit-wise manipulations. It worked out perfectly, even the performance is very good.

' Create byte array for the main ploted TIF image
Dim bmp As New Drawing.Bitmap(Img.Width, Img.Height, Drawing.Imaging.PixelFormat.Format1bppIndexed)
bmp = Img   ' getting bitmap from the default image
Dim data As System.Drawing.Imaging.BitmapData = bmp.LockBits(New Drawing.Rectangle(0, 0, bmp.Width, bmp.Height), Drawing.Imaging.ImageLockMode.[WriteOnly], Drawing.Imaging.PixelFormat.Format1bppIndexed)
Dim bytes As Byte() = New Byte(data.Height * data.Stride - 1) {}
System.Runtime.InteropServices.Marshal.Copy(data.Scan0, bytes, 0, bytes.Length)


' Create byte array for the banner
Dim bmpB As New Drawing.Bitmap(Img.Width, Img.Height, Drawing.Imaging.PixelFormat.Format1bppIndexed)
bmpB = Img.Clone()   ' banner had to be generated in 16bppp unindexed gray scale image to be able to use graphics
Dim dataB As System.Drawing.Imaging.BitmapData = bmpB.LockBits(New Drawing.Rectangle(0, 0, BmpB.Width, BmpB.Height), Drawing.Imaging.ImageLockMode.[WriteOnly], Drawing.Imaging.PixelFormat.Format1bppIndexed)
Dim bytesB As Byte() = New Byte(dataB.Height * dataB.Stride - 1) {}
System.Runtime.InteropServices.Marshal.Copy(dataB.Scan0, bytesB, 0, bytesB.Length)


' Join byte arrays:  Resulting bitmap = plotted TIF + banner
Dim bytesResult((bytes.Length + bytesB.Length) - 1) As Byte
bytesB.CopyTo(bytesResult, 0)
bytes.CopyTo(bytesResult, bytesB.Length)


' Revert resulting byte array back to bitmap and save resulting TIF image
BmpResized = New Bitmap(Img.Width, Img.Height * 2, Drawing.Imaging.PixelFormat.Format1bppIndexed)
Dim dataResult As System.Drawing.Imaging.BitmapData = BmpResized.LockBits(New Drawing.Rectangle(0, 0, BmpResized.Width, BmpResized.Height), Drawing.Imaging.ImageLockMode.[WriteOnly], Drawing.Imaging.PixelFormat.Format1bppIndexed)
System.Runtime.InteropServices.Marshal.Copy(bytesResult, 0, dataResult.Scan0, bytes.Length + bytesB.Length - 0)
Dim exportFileName As String = filenames1(0).Replace(".tif", "_mod.tif")
exportFileName = exportFileName.Replace(".png", "_mod.tif")
BmpResized.Save(exportFileName, Drawing.Imaging.ImageFormat.Tiff)

' Unlock locked bitmaps
bmp.UnlockBits(dataResult)
BmpResized.UnlockBits(dataResult)

' dispose anything not used later...