More Examples of Simplified Image Processing in GDI+ - Sample Six-Working with Thumbnail Images

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In the commonly used picture viewer applications, such as AcdSee, Windows Explorer, a thumbnail gives an outline of a real image. Using GDI+, you can easily achieve the purpose of rendering a thumbnail of an image.

The following shows the signature of the GetThumbnailImage() method:

// Summary:

// Returns a thumbnail for this System.Drawing.Image.

// Parameters:

// thumbWidth:

// The width, in pixels, of the requested thumbnail image.

// thumbHeight:

// The height, in pixels, of the requested thumbnail image.

// callback:

// A System.Drawing.Image.GetThumbnailImageAbort delegate. In GDI+ version 1.0,

// the delegate is not used. Even so, you must create a delegate and pass a

// reference to that delegate in this parameter.

// callbackData:

// Must be System.IntPtr.Zero.

// Returns:

// An System.Drawing.Image that represents the thumbnail.

public Image GetThumbnailImage(int thumbWidth, int thumbHeight, Image.GetThumbnailImageAbort callback, IntPtr callbackData);

As shown from the above definition, a thumbnail is based upon a whole image; it is in fact only a copy of the original image. In addition, the user can specify the size of a thumbnail of an image-maybe even larger than the original. Next, let us take a close look at a related sample application.

Graphics graphics=this.CreateGraphics();

graphics.Clear(Color.White);

//set up the interpolation mode-HighQualityBicubic

graphics.InterpolationMode=InterpolationMode.HighQualityBicubic;

//load the image to be shown as thumbnails

Bitmap image=new Bitmap("flower.bmp");

//obtain the size of the current window

Rectangle client=new Rectangle(0,0,

this.ClientSize.Width,this.ClientSize.Height);

float width=image.Width;

float height=image.Height;

//get a thumbnail of specified size

Image.GetThumbnailImageAbort myCallback =

new Image.GetThumbnailImageAbort(ThumbnailCallback);

Image pThumbnail = image.GetThumbnailImage(40,40, myCallback ,IntPtr.Zero);

//use the thumbnail as a brush

TextureBrush picBrush=new TextureBrush(pThumbnail);

//fill in the window

graphics.FillEllipse(picBrush,client);

Since there are already enough comments in the code, we will not dwell on it. Figure 7 gives the associated running-time snapshot.

Figure 7-the associated running-time snapshot of the thumbnail effect

Next: Sample Seven-Cloning an Image >>
 

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