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Posted 28 Sep 2006
Licenced Ms-PL

Pan and Zoom Very Large Images

, 31 Oct 2009
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Smoothly panning and zooming very large images can be a challenge. Here’s a control, with source code, that demonstrates one way of overcoming this challenge, as well as a few "Extra" image processing features.

Note: This was written against .NET 2.0, then manually converted to .NET 1.1.

Sample image


I recently wrote an article showing a simple method for panning an image. The code worked very well for small to moderate sized images. However, when using very large images, the performance degraded significantly.

That article used a picture box within a panel, and used the auto scroll functionality of the panel to perform scrolling. I received quite a bit of feedback indicating the need for a version that could handle very large images and still pan very smoothly. I also received requests for ideas on how to zoom the image in and out. So, I got to work.

What I came up with is a control that could smoothly pan super-sized images, and also provided zoom functionality. My tests were with a 49MB GIF (7000 x 7000). The performance was very smooth. Of course, the control works equally as well with small images. The control is demonstrated in the included sample project.

This custom control does not use a picture box, nor does it inherit from one. Neither is there a panel or any "auto-scrolling". This is very different and very much a better way of panning an image (in my opinion). An added benefit to this example is the ability to zoom the image without resizing a picture box (which can get quite large in memory).

How It Works

  1. Only paints the part of the image currently visible.
  2. Double-buffering provides flicker free panning.
  3. GDI+ automatically scales the image for us.

Public Properties

  • Public Property PanButton() As System.Windows.Forms.MouseButtons
  • Public Property ZoomOnMouseWheel() As Boolean
  • Public Property ZoomFactor() As Double
  • Public Property Origin() As System.Drawing.Point

Public Shadows

  • Public Shadows Property Image() As System.Drawing.Image
  • Public Shadows Property initialimage() As System.Drawing.Image

Public Methods

  • Public Sub ShowActualSize()
  • Public Sub ResetImage()

Using the control is as simple as using a standard PictureBox. First, drop the control on a form, then when you need to show an image, you can do it this way:

Dim bmp As New Bitmap("Image.jpg")
Me.ImageViewer1.Image = bmp

Don't forget to change the filename!

It is important to note: If you are working with very large images, you should not pre-load them in the designer. This seriously bloats the project, and can result in "Out of Memory" issues. Instead, load your images during run-time.

Default Behavior

  • Panning the image: Click and hold the left mouse button while the cursor is over the image. Then, simply move your mouse around, with the button still depressed.
  • Zooming: Make sure the control has focus (click the image). Then, use your mouse wheel to zoom in and out.

Customized Usage

You can tell the control what button to use for panning, with the "PanButton" property. You can turn off the default zooming by setting the ZoomOnMouseWheel property to False.

You can manually set the zoom factor so you could implement your own zoom functionality (i.e., using a slider, or buttons).

You can move the image around programmatically by setting the origin. The origin property gets or sets the coordinates of the top left corner of the viewable window in relation to the original image. For example, if you wanted to see the bottom right corner of an image with a size of 5000 x 5000, and your viewable control size was 500 pixels x 500 pixels, you could set the origin to 4500, 4500. This assumes, of course, that you have a zoom factor of 1 (not zoomed in or out).

You could catch the paint event of the control and overlay your own graphics. Just be careful to take the zoom factor into consideration if you need to draw at precise coordinates in relation to the original image.


Due to popular demand, scrollbars have now been implemented.

Double Buffering

Double buffering is accomplished by setting the control styles in the constructor as such:

Public Sub New()
     'This call is required by the Windows Form Designer.
     'Add any initialization after the InitializeComponent() call
     Me.SetStyle(ControlStyles.AllPaintingInWmPaint, True)
     Me.SetStyle(ControlStyles.DoubleBuffer, True)
End Sub

Just In Time Painting?

Well, sort of. While we do have a copy of the image in memory, we only paint the area currently viewable.

Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs)
End Sub

Protected Overrides Sub OnSizeChanged(ByVal e As EventArgs)
     DestRect = New System.Drawing.Rectangle(0, 0, _
                    ClientSize.Width, ClientSize.Height)
End Sub

Private Sub DrawImage(ByRef g As Graphics)
     If m_OriginalImage Is Nothing Then Exit Sub
     SrcRect = New System.Drawing.Rectangle(m_Origin.X, m_Origin.Y, _
                          ClientSize.Width / m_ZoomFactor, _
                          ClientSize.Height / m_ZoomFactor)
     g.DrawImage(m_OriginalImage, DestRect, SrcRect, GraphicsUnit.Pixel)
End Sub

Note that we are taking the current zoom factor into consideration when drawing. By using the DrawImage method of the Graphics object, GDI will scale the image from the source area to fit the destination area.

Panning the Image

The code for panning the image and keeping the zoom factor in mind, is as follows:

Private Sub ImageViewer_MouseMove(ByVal sender As Object, _
        ByVal e As System.Windows.Forms.MouseEventArgs) _
        Handles MyBase.MouseMove

     'Make sure we are panning on the correct mouse button
     If e.Button = m_MouseButtons Then
          Dim DeltaX As Integer = m_PanStartPoint.X - e.X
          Dim DeltaY As Integer = m_PanStartPoint.Y - e.Y

          'Set the origin of the new image
          m_Origin.X = m_Origin.X + (DeltaX / m_ZoomFactor)
          m_Origin.Y = m_Origin.Y + (DeltaY / m_ZoomFactor)

          'Make sure we don't go out of bounds
          If m_Origin.X < 0 Then m_Origin.X = 0
          If m_Origin.Y < 0 Then m_Origin.Y = 0

          If m_Origin.X > m_OriginalImage.Width - _
                         (ClientSize.Width / m_ZoomFactor) Then
               m_Origin.X = _m_OriginalImage.Width - _
                            (ClientSize.Width / m_ZoomFactor)
          End If
          If m_Origin.Y > m_OriginalImage.Height - _
                           (ClientSize.Height / m_ZoomFactor) Then
               m_Origin.Y = m_OriginalImage.Height - _
                           (ClientSize.Height / m_ZoomFactor)
          End If

          If m_Origin.X < 0 Then m_Origin.X = 0
          If m_Origin.Y < 0 Then m_Origin.Y = 0

          'reset the startpoints
          m_PanStartPoint.X = e.X
          m_PanStartPoint.Y = e.Y

          'Force a paint
     End If
End Sub


Many of the concepts used within this example project are worthy of their own discrete articles. Therefore, I didn't go into any great detail about what double buffering is, nor did I dive into the intricacies of GDI+ in .NET. However, I hope that I have adequately covered the basics of how this control works, as well as how you can use it.

Please Note...

This is by no means meant to be a complete solution, nor is this code "production-ready". Then too, there are usually many ways to solve a problem; this is one. Hopefully, though, this sample has proven beneficial in some way. Perhaps, this article has given you a great idea about how to do this a better way, or an idea for expanding what is presented here. Great! That's why I wrote it. Please feel free to leave some feedback. Let me know how it went for you. If you do have an idea on how to improve this example or this article, please let me know that too.

P.S.: Don't forget to vote! If you don't have an account, make one!

Revisions and Bug Fixes ...

  • 02/04/2007
    • Added scrollbar functionality
    • Fixed null image bug
    • Fixed memory leak
    • Implemented several performance improving suggestions
    • Added ability to invert colors
    • Added ability to stretch image or set to actual pixels
    • Removed the hard coded image file and added dialogue box to test harness
  • 02/06/2007
    • Added a .NET 1.1 version
  • 30/10/2009
    • Deleted the .NET 1.1 zip file


  1. Change Points to PointF and Rectangles to RectangleF to allow finer panning and scrolling when zoomed in very tight
  2. Update the article to dissect the app and explain why it works the way it does
  3. Update the code presented in the article

Thanks for your patience!


This article, along with any associated source code and files, is licensed under The Microsoft Public License (Ms-PL)


About the Author

Anthony Queen
Software Developer (Senior)
United States United States
I started my career in software development back in 2000. Prior to that, I made my living as a detail drafter. My true start in programming, though, goes back much further. I first started learning to program when I was about 10 years old. It was back in ‘82 that I wrote my first application. It was a simple calculator program written on a TRS-80 that my uncle had. Since then, I’ve programmed in Basic, QuickBasic, Pascal, C++, VB 6, VB.NET, Java, HTML, and C #. I have a very diverse background. I’ve worked and written software for several types of companies, including manufacturing, engineering, and finance. I’ve had the opportunity to design and maintain a few enterprise level databases, I’ve written applications to run on windows CE, in a wireless manufacturing environment. I’ve also had opportunities to teach OOP methodologies, and design patterns. I thoroughly enjoy what I do, and my only regret is that I didn’t start sooner.

Comments and Discussions

GeneralRe: Change Request: Keeping the image centered Pin
adrianh_za10-Feb-07 21:42
memberadrianh_za10-Feb-07 21:42 
GeneralRe: Change Request: Keeping the image centered Pin
adrianh_za15-May-07 7:17
memberadrianh_za15-May-07 7:17 
GeneralRe: Change Request: Keeping the image centered Pin
Anthony Queen15-May-07 16:58
memberAnthony Queen15-May-07 16:58 
QuestionWhat about DirectCast? Pin
Mohammed Abd Alla7-Feb-07 3:53
memberMohammed Abd Alla7-Feb-07 3:53 
AnswerRe: What about DirectCast? Pin
Anthony Queen7-Feb-07 10:38
memberAnthony Queen7-Feb-07 10:38 
GeneralComment and Suggestion Pin
Ilíon20-Jan-07 16:51
memberIlíon20-Jan-07 16:51 
GeneralRe: Comment and Suggestion Pin
Anthony Queen21-Jan-07 8:15
memberAnthony Queen21-Jan-07 8:15 
GeneralRe: Comment and Suggestion Pin
Ilíon21-Jan-07 15:51
memberIlíon21-Jan-07 15:51 
"However, my has been extremely limited the last several weeks ..."
That's OK, I certainly understand. I noticed your earlier note about being time-limited, but I thought you might like a bit of feedback to think about for your next update.

As for the computation of the ratios, I'm originally a mainframe programmer (originally using Assembler). One of the primary "rules" in that world is "don't do a computation inside a loop unless it really is necessary for the loop's logic." So, even though I wasn't studying your code in-depth, that sort of just jumped out at me.

"Now, as to your memory issue, are you loading the image at design time or run time?"
No, I'm loading the images (plural) at runtime.

What I'm *hoping* to be able to do in the finished project is hold in memory 500 to 1000 "preview-sized" versions of the images being processed. This will significantly speed up the user's experience of using the application.

It's really strange, what's happening in my testing.

I've been testing my logic for "navigating" through the images being processed using the images in a folder containing over 400 JPEG images. This files probably average @150KB, with a typical resolution of 500(w) X 744(h).

I haven't *noticed* a problem using these images -- and at the time, I was using the *entire* image, rather than a reduced resolution "preview" version. I can load all the images into active memory two or three times (I duplicated the folder to get unique paths) without noticing a problem.

However, I have another folder of test images, which are more realistically sized, at a bit over 2000(w) X 3000(h) (I'd say they average 600-700KB as JPEG files).

There are only 160 of these more realistically sized images, and I invariably get an "out of memory" exception when I try to use them ... regardless of whether I try to hold the full 2000x3000 image, or a resized 454x568 version. I also eventually get the exception when I hold only 50 (as opposed to all 160) in active memory.

To make it even more outrageous, I even get the exception when I don't actually hold them in memory!

What I mean is:
1) If I read in all 160 in sequence into a byte-array (but do nothing further and thus keep "throwing away" each image), I don't get the expection. But I also don't have any images to work with.
2) If I convert the individual byte-arrays to an image-object and then dispose of the image-object, I don't get the expection. But I also don't have any images to work with.
3) However, if I then try to produce a thumbnail or preview version of the images, even though at that time in testing I'm still disposing of everything, I get the exception.
4) If I save ALL 160 byte-arrays into DataSet.Table.Row objects, I don't get the exception ... until I start converting them to images as I "navigate" through the set of images.

It's very frustrating.

Of course, I don't expect you to resolve this problem for me ... but you indicated a bit of interest. So, any thoughts you have are welcome.
GeneralRe: Comment and Suggestion Pin
Anthony Queen22-Jan-07 3:16
memberAnthony Queen22-Jan-07 3:16 
GeneralRe: Comment and Suggestion Pin
Ilíon22-Jan-07 4:05
memberIlíon22-Jan-07 4:05 
GeneralRe: Comment and Suggestion Pin
Ilíon22-Jan-07 4:34
memberIlíon22-Jan-07 4:34 
GeneralRe: Comment and Suggestion Pin
Anthony Queen22-Jan-07 4:54
memberAnthony Queen22-Jan-07 4:54 
NewsSorry for no response lately. Pin
Anthony Queen10-Jan-07 3:27
memberAnthony Queen10-Jan-07 3:27 
Generalproblem in scrollbar Pin
Mausumi10-Jan-07 1:33
memberMausumi10-Jan-07 1:33 
GeneralRe: problem in scrollbar Pin
Anthony Queen10-Jan-07 3:28
memberAnthony Queen10-Jan-07 3:28 
AnswerRe: problem in scrollbar Pin
Anthony Queen6-Feb-07 6:14
memberAnthony Queen6-Feb-07 6:14 
QuestionScrollbars Request and Several Bugfixes Pin
Mergandevin4-Jan-07 2:57
memberMergandevin4-Jan-07 2:57 
AnswerRe: Scrollbars Request and Several Bugfixes Pin
Anthony Queen6-Feb-07 4:29
memberAnthony Queen6-Feb-07 4:29 
AnswerRe: Scrollbars Request and Several Bugfixes Pin
Anthony Queen6-Feb-07 6:14
memberAnthony Queen6-Feb-07 6:14 
GeneralInitial zoom of 0.5 causes slow panning updates Pin
jonesst993-Jan-07 4:00
memberjonesst993-Jan-07 4:00 
GeneralRe: Initial zoom of 0.5 causes slow panning updates Pin
jonesst993-Jan-07 21:56
memberjonesst993-Jan-07 21:56 
GeneralAdditional imagviewer Pin
Gridaksma21-Dec-06 7:12
memberGridaksma21-Dec-06 7:12 
AnswerRe: Additional imagviewer Pin
Anthony Queen22-Dec-06 4:48
memberAnthony Queen22-Dec-06 4:48 
AnswerRe: Additional imagviewer Pin
98z2814-Feb-07 16:59
member98z2814-Feb-07 16:59 
GeneralRefresh when .image = nothing Pin
the bill7-Nov-06 4:09
memberthe bill7-Nov-06 4:09 

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