Subroutine ShrinkImage makes a Bitmap to represent the input image. It then creates a new Bitmap that is half as tall and wide as the input image. If it should antialias, it sets the Graphics object's InterpolationMode property to HighQualityBilinear. It then uses the Graphics object's DrawImage method to copy the source Bitmap into the result Bitmap and displays the results.

Private Sub Form1_Load(ByVal sender As System.Object, ByVal _
    e As System.EventArgs) Handles MyBase.Load
    ShrinkImage(picOriginal, picNotAntialiased)
    ShrinkImage(picOriginal, picAntialiased, True)
End Sub

Private Sub ShrinkImage(ByVal from_pic As PictureBox, ByVal _
    to_pic As PictureBox, Optional ByVal anti_alias As _
    Boolean = False)
    ' Get the source Bitmap.
    Dim from_bm As New Bitmap(from_pic.Image)

    ' Make the destination Bitmap.
    Dim wid As Integer = from_pic.Width \ 2
    Dim hgt As Integer = from_pic.Height \ 2
    Dim to_bm As New Bitmap(wid, hgt)

    ' Copy the image.
    Dim gr As Graphics = Graphics.FromImage(to_bm)
    If anti_alias Then gr.InterpolationMode = _
        Drawing2D.InterpolationMode.HighQualityBilinear
    gr.DrawImage(from_bm, 0, 0, wid - 1, hgt - 1)

    ' Display the result.
    to_pic.Image = to_bm
End Sub