vb.net how can zoom image - vb.net

Question

I have a Custom Control for viewing images with zooming facility but without scrollBar, and its working condition is good. Actually The Custom Control is a Panel with a Picutrbox on it. I also using a TrackBar for zooming in/out the image. It is also working better.
But I am not fully satisfied, even it is covering the purpose of my App because I need zooming PictureBox based on center point. Now it is anchoring Top Left.
Another One is when Zooming out the image, the image goes to zero size at TrackBar's Zero. Even I limited zoom level to the panel size and working good, my unsatisfaction taking place here also, as it is not responding at zero level of TrackBar. Here I need, the original size of image loaded in picture box have to go for 100% of TrackBar and when image reached at Custom controle size have to go for 0% of TrackBar. Then I will fullfilled.
I figuring my code here.........
My Custom Control is a User Control Inheriting from Panel.
code for cutom control :
Public Class ImageViewer
Inherits Panel
Dim AutoScaleDimensions As SizeF
Dim AutoScaleMode As AutoScaleMode
Protected Overrides Sub DefWndProc(ByRef m As Message)
If m.Msg <> 131 Then
MyBase.DefWndProc(m)
End If
End Sub
End Class
On Form1, I Placed my Custom Control- ImageViewer1 and also placed PicutreBox1 with in ImageViewer1, Palced Button1 and TrackBar1 on Form1
Changed Properties as follows
ImageViewer1 - AutoScroll=True
PicutreBox1 - SizeMode=Zoom
TrackBar1- Maximum=100
My Declared Variables are
Dim imgName As String
Private SliderCenter As Integer = 50
Private originalImg As Bitmap
Code for Button1.Click
Try
Dim inputImg As FileDialog = New OpenFileDialog()
inputImg.Filter = "Image File (*.Jpg;*.Bmp;*.Png;*.Gif;*.Tiff;*.Tif;*.PDF)|*.Jpg;*.Bmp;*.Png;*.Gif;*.Tiff;*.Tif;*.PDF"
If inputImg.ShowDialog() = DialogResult.OK Then
imgName = inputImg.FileName
originalImg = New Bitmap(inputImg.FileName)
Dim newImg As New Bitmap(imgName)
PictureBox1.Image = DirectCast(newImg, Image)
End If
inputImg = Nothing
Catch ae As System.ArgumentException
imgName = ""
MessageBox.Show(ae.Message.ToString)
Catch ex As Exception
MessageBox.Show(ex.Message.ToString)
End Try
Code for TrackBar1.ValueChanged
If originalImg IsNot Nothing Then
If TrackBar1.Value > 0 Then
Dim scale As Double = TrackBar1.Value
Dim height As Integer = Convert.ToInt32((scale / SliderCenter) * originalImg.Height)
Dim width As Integer = Convert.ToInt32((scale / SliderCenter) * originalImg.Width)
PictureBox1.Size = New Size(width, height)
If PictureBox1.Width <= ImageViewer1.Width Then
PictureBox1.Size = New Size(PictureBox1.Width + (ImageViewer1.Width - PictureBox1.Width), ImageViewer1.Height)
End If
If PictureBox1.Height <= ImageViewer1.Height Then
PictureBox1.Size = New Size(ImageViewer1.Width, PictureBox1.Height + (ImageViewer1.Height - PictureBox1.Height))
End If
End If
End If
Please help me in your kind ........ Thank You.