How to Create Thumbnail Images in C#
A thumbnail is a small sized image. Creating a thumbnail using .NET is extremely simple. In this article, we will explore how to create a thumbnail image and display the thumbnail in our application. Follow these steps:
Step 1: Open Visual Studio 2005/2008. File > New > Project > Visual C# or Visual Basic > Windows Application. Enter the name of the application and click Ok.
Step 2: Drag and drop a label, 2 button controls and an OpenFileDialog component to the form. Rename them as follows:
Label1 – lblFile
Button1 – btnOpen
Button2 – btnGenerateThumbnail
TextBox – txtFileNm
OpenFileDialog – Set the Filter to ‘JPG Files|*.jpg’
Step 3: On the ‘btnOpen’ click, display the File Open dialog box and accept the selected .jpg file in the txtFileNm textbox.
C#
private void btnOpen_Click(object sender, EventArgs e)
{
if (openFileDialog1.ShowDialog() == System.Windows.Forms.DialogResult.OK)
{
txtFileNm.Text = openFileDialog1.FileName;
}
}
Step 4: Next, on the ‘btnGenerateThumbnail’ click, add the following code:
C#
// Declare a class level variable
Image imgThumb = null;
private void btnGenerateThumbnail_Click(object sender, EventArgs e)
{
try
{
Image image = null;
// Check if textbox has a value
if (txtFileNm.Text != String.Empty)
image = Image.FromFile(txtFileNm.Text);
// Check if image exists
if (image != null)
{
imgThumb = image.GetThumbnailImage(100, 100, null, new IntPtr());
this.Refresh();
}
}
catch
{
MessageBox.Show("An error occured");
}
}
The code creates an Image object from the image supplied in the textbox. Using the Image.GetThumbnailImage(), the code then creates a thumbnail image with a size of 100*100.
The Image.GetThumbnailImage() takes in four arguments :
Width, in pixel of the thumbnail image that is to be generated
Height, in pixel of the thumbnail image that is to be generated
Callback, a Image.GetTumbnailImageAbort delegate to prematurely cancel execution
CallbackData, of type IntPtr to represent a pointer or a handle.
Step 5: The final step is to add the Paint event which is called using this.Refresh() in the button click. The thumbnail image is drawn on the form.
C#
private void Form1_Paint(object sender, PaintEventArgs e)
{
if(imgThumb != null)
e.Graphics.DrawImage(imgThumb,30, 20, imgThumb.Width, imgThumb.Height);
}
Run the application, select the image and click on the Generate button. The preview will be similar to the image displayed below :
You can actually extend this example to 'save' the generated thumbnails. Something like a ‘Thumbnail Creator’ program. You can loop through a folder containing images and generate thumbnail images for all the images in the folder. I would encourage you to try out these ideas.
