TIFF to PDF convert - PDF filesize getting over 3 times as big

Hi, im trying to convert the attached TIFF to PDF using the following code:

        Dim pdf1 As Pdf = New Pdf()
        Dim sec As Section = pdf1.Sections.Add()

        Dim ms As MemoryStream = New MemoryStream(<File>)
        Dim myimage As New Bitmap(ms)

        Dim imageht As Aspose.Pdf.Generator.Image = New Aspose.Pdf.Generator.Image(sec)
        imageht.ImageInfo.ImageFileType = ImageFileType.Tiff
        imageht.ImageInfo.ImageStream = ms
        imageht.ImageInfo.IsBlackWhite = false
        sec.Paragraphs.Add(imageht)

        Dim tifstream = New MemoryStream()
        pdf1.Save(tifstream)

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The tif size is 285 kb
The converted PDF file is 954kb

When I set the "IsBlackWhite" to "true", the PDF filesize drops to 300kb.
But im not intererested in converting the tiff to BlackWhite.

How can I convert the TIFF to PDF without the filesize getting much bigger?