In Powershell convert image to BMP 16 bits

I have a code to batch convert a folder of jpg files to BMP.

The code i have works OK, but it gets saved as BMP 24 bits.

I need it to convert it to BMP 16 bits using Powershell

function ConvertImage{

$Origen="C:\jpg" #path to files
$Destino="C:\bmp" #path to files

if (Test-Path $Origen)
{
#Load required assemblies and get object reference
 [Reflection.Assembly]::LoadWithPartialName("System.Windows.Forms") | Out-Null
 foreach($file in (Get-ChildItem -Path "$Origen\*.jpg" -Exclude *-*)){
     $convertfile = new-object System.Drawing.Bitmap($file.Fullname)
     $newfilname = $Destino + '\' + $file.BaseName + '.bmp'
     $convertfile.Save($newfilname, "bmp")
     $file.Fullname
    }  
 }
    else
 {
    Write-Host "Path not found."
 }
};ConvertImage -path $args[0]