EXCELL 文档转换成图片，32 位图如何转换成 24 位图

Public Function ConvertExcelTOImage() As String
        Dim excelFilePath As String = "E:\Picture\运行图甲.xls"
        Dim SaveExcelJPG As String = "E:\Picture\111.bmp"
        Dim app As Microsoft.Office.Interop.Excel.Application = New Microsoft.Office.Interop.Excel.Application()
        app.CutCopyMode = False
        app.Visible = False
        Dim objMis As Object = Type.Missing
        Dim singleExcel As Microsoft.Office.Interop.Excel.Workbook = app.Workbooks.Open(excelFilePath, objMis, objMis, objMis, objMis, objMis, objMis, objMis, objMis, objMis, objMis, objMis, objMis, objMis, objMis)
        Try
            Dim wsheet As Microsoft.Office.Interop.Excel.Worksheet = singleExcel.Worksheets(1)
            Dim ranobj As Object = DBNull.Value
            wsheet.Range("B2", "G3").Copy(ranobj)
            Dim iData As IDataObject = Clipboard.GetDataObject()
            Dim bits As Bitmap = iData.GetData(DataFormats.Bitmap)
            Dim myBitmap As Bitmap = New Bitmap(bits.Width, bits.Height)
            Dim g As Graphics = Graphics.FromImage(myBitmap)
            g.DrawImage(bits, -1, -1)
            myBitmap.Save(String.Format(SaveExcelJPG, Guid.NewGuid()))
            Clipboard.Clear()
            myBitmap.Dispose()
            bits.Dispose()
            Return ""
        Catch ex As Exception
            ' KillProcess("EXCEL")
            Return ex.Message
        Finally
            Clipboard.Clear()
            ' KillProcess("EXCEL")
        End Try
    End Function
上述程序是，将EXCELL文件转换成32位图图片，如何能让转换的图片是24位的呢？