Image Viewer Items

ImageViewer supports one or more items with each containing its own image data, size and optional additional transformation.

Using Items

To access the items, use the ImageViewer.Items property. This is of type ImageViewerItems which implements standard ICollection and IList interfaces to easily add/remove/get/set and enumerate the items:

When an items list or the properties of an item has changed, the following events occur in the image viewer:

In addition to the above standard collection operations, ImageViewerItems supports the following:

The items are arranged for viewing using the layout system. For more information, refer to Image Viewer Layouts.

A new item can be added to the viewer using any of the following:

• From raster image data in a RasterImage object
• From SVG image data in anSvgDocument object
• From a URL containing raster or SVG image data
• As an empty item (without any image data, just size information)

For code snippets below, replace the code used in Using Image Viewer with Windows.Forms with the snippet below, then add the code described.

Generic Code

// Create a new image viewer instance with a vertical layout 
ImageViewerViewLayout viewLayout = new ImageViewerVerticalViewLayout(); 
ImageViewer imageViewer = new ImageViewer(viewLayout); 
// Set some properties 
imageViewer.Dock = DockStyle.Fill; 
imageViewer.BackColor = Color.Bisque; 
// Add a border (need some padding as well) 
imageViewer.ImageBorderThickness = 1; 
imageViewer.ItemPadding = new Padding(imageViewer.ImageBorderThickness); 
// Add it to the form 
this.Controls.Add(imageViewer); 
imageViewer.BringToFront(); 
// Add pan/zoom interactive mode. Click and drag to pan the image and ctrl-click 
// and drag to zoom in/out 
imageViewer.InteractiveModes.Add(new ImageViewerPanZoomInteractiveMode()); 

Adding and Removing Items

The following code will create a new item, load a TIF file as a RasterImage, set it as the image data of the item, and add the item to the viewer:

// Create an item 
ImageViewerItem item = new ImageViewerItem(); 
// Load an image into it 
using (RasterCodecs codecs = new RasterCodecs()) 
   item.Image = codecs.Load(@"C:\LEADTOOLS22\Resources\Images\Ocr1.tif", 1); 
// Add it to the viewer 
imageViewer.Items.Add(item); 

Alternatively, let the viewer load it (using the internal RasterCodecs instance) by setting the URL:

// Create an item 
ImageViewerItem item = new ImageViewerItem(); 
// Load an image into it 
item.Url = new Uri(@"C:\LEADTOOLS22\Resources\Images\Ocr1.tif"); 
// Add it to the viewer 
imageViewer.Items.Add(item); 

It is also possible to use the ImageViewerItems method to add the items directly without creating an ImageViewerItem instance:

// Add an item directly 
using (RasterCodecs codecs = new RasterCodecs()) 
{ 
   RasterImage rasterImage = codecs.Load(@"C:\LEADTOOLS22\Resources\Images\Ocr1.tif", 1); 
   imageViewer.Items.AddFromImage(rasterImage, 1); 
} 

Another way is to add an item from a file directly without creating a RasterImage object:

// Add an item directly from a disk file 
imageViewer.Items.AddFromImageFile(@"C:\LEADTOOLS22\Resources\Images\Ocr1.tif", 1); 

Or from a URL

// Add an item directly from a URL 
imageViewer.Items.AddFromImageUrl(new Uri(@"C:\LEADTOOLS22\Resources\Images\Ocr1.tif")); 

In the cases above, the item added can be easily obtained for further modification by using the return values from the methods or accessing the ImageViewer.Items collection.

ImageViewer also supports adding SVG items. They can be SVG files or any document format that supports being loaded as SVG. This code will load a page from a PDF file as SVG and add an item for it:

// Create an item 
ImageViewerItem item = new ImageViewerItem(); 
// Load a page from a PDF file as SVG and set it in the item 
using (RasterCodecs codecs = new RasterCodecs()) 
   item.SvgDocument = codecs.LoadSvg(@"C:\LEADTOOLS22\Resources\Images\Leadtools.pdf", 1, null) as SvgDocument; 
// Add it to the viewer 
imageViewer.Items.Add(item); 

Similarly to using RasterImage, the viewer can load the SVG document by setting the URL. An extra step is required:

// Create an item 
ImageViewerItem item = new ImageViewerItem(); 
// Tell the item to load the data in the URL as SVG, not a RasterImage 
item.LoadUrlAsSvg = true; 
// Load an image into it 
item.Url = new Uri(@"C:\LEADTOOLS22\Resources\Images\Leadtools.pdf"); 
// Add it to the viewer 
imageViewer.Items.Add(item); 

AddFromSvgDocument, AddFromSvgUrl or AddFromSvgFile work the same way as the RasterImage counterparts described above.

The following code adds four items to the viewer:

// Add an item directly 
using (RasterCodecs codecs = new RasterCodecs()) 
{ 
   for (int i = 1; i <= 4; i++) 
   { 
      string fileName = string.Format(@"C:\LEADTOOLS22\Resources\Images\Ocr{0}.tif", i); 
      RasterImage rasterImage = codecs.Load(fileName, 1); 
      imageViewer.Items.AddFromImage(rasterImage, 1); 
   } 
} 
// pan and zoom to see all the images on top of each other 

It is best to disable the viewer from updating while multiple items are added (or removed, or updated). Doing so ensures that the viewer does not waste resources updating its transformations and re-painting while it is in an intermediate state:

// Disable any updates till we are done 
imageViewer.BeginUpdate(); 
// Add an item directly 
using (RasterCodecs codecs = new RasterCodecs()) 
{ 
   for (int i = 1; i <= 4; i++) 
   { 
      string fileName = string.Format(@"C:\LEADTOOLS22\Resources\Images\Ocr{0}.tif", i); 
      RasterImage rasterImage = codecs.Load(fileName, 1); 
      imageViewer.Items.AddFromImage(rasterImage, 1); 
   } 
} 
// Update now 
imageViewer.EndUpdate(); 
// pan and zoom to see all the images on top of each other 

With multiple items, it is sometimes desired to add items at a certain location. This can easily be accomplished using ImageViewerItems.Insert which accepts as a parameter the index of the new item. All the direct add methods (such as AddFromImage) also have an insert counterpart (Such as InsertFromImage)

Removing items from the viewer is performed as follows. Start from the example code above and add the following:

// Remove the first item 
imageViewer.Items.RemoveAt(0); 

Run the demo again. Note that the viewer is displaying three items instead of four, starting from page 2. ImageViewerItems.Remove can be used to remove an item by its reference. ImageViewerItems.Clear will remove all the items from the viewer (and set the ActiveItem property to null)

Relationship between Item and Image Size

Each ImageViewerItem has two properties to determine the size of the item and its image:

When using the control as an "image" or "document" viewer, then in most cases these two values are the same and the image will occupy the whole item area.

When using the control as an "image list" or "thumbnails" viewer, then it is desirable to have the item size larger than the image size to leave room for text description (for example).

In both cases, each item can have its own item and image size different than any other item in the viewer.

Image Size

The viewer will calculate and set ImageViewerItem.ImageSize depending on the following conditions:

Item Size

The viewer calculates and sets ImageViewerItem.Size depending on following conditions:

Usually you set ImageViewer.ItemSize to a specified value when the viewer is used as an "image list" or "thumbnails browser". To accomplish this, set the value of ItemSize to the desired thumbnail size plus padding (for example, 200 by 200 pixels). Then add the items with their own ImageViewerItem.Size set to the default value of LeadSize.Empty. As described above, the viewer will update ImageViewerItem.Size to be equal to 200 by 200 pixels as well. One more thing to consider in this mode is how the image inside each item is displayed. In image list mode, it is probably desired to fit each image inside this size (200 by 200 pixels in the case above), so set the value of ImageViewer.ItemSizeMode to Fit or FitAlways.

Resolution

ImageViewerItem also has the Resolution property. This must be set to the resolution (in dots per inch) of the original image data, if accounting for the logical size of the image when displayed is desired.

The resolution is only used when ImageViewer.UseDpi is set to true. The values of ImageViewerItem.Resolution along with ImageViewer.ScreenDpi are used when calculating how to display the image.

For example, a typical US Letter document image is 8.5 by 11 inches, which at the typical print resolution of 300 by 300 dpi is equivalent to 2550 by 3300 pixels. Most document viewer applications will try to display this image at its original size (i.e., the image will take 8.5 inches of screen horizontal space and 11 inches of screen vertical space).

If you do not use the ImageViewer.UseDpi property for this control, you are required to do the calculations yourself as follows:

viewer.UseDpi = false; 
viewer.Zoom(screenResolution / imageResolution); 

In the case of the image above, this will be 96 (typical screen resolution) divided by 300. Or, set the ImageViewer.UseDpi value to true and the control will use the above formula internally, keeping the ScaleFactor set to 1 as follows:

viewer.UseDpi = true; 
viewer.Zoom(1); 

This code produces the same results as the first code snippet.

In platforms where the screen resolution can be obtained programmatically (such as Windows.Forms), the value of ImageViewer.ScreenDpi is set automatically by the image viewer upon creation.

In platforms where the screen resolution cannot be obtained programmatically (such as JavaScript), the value of ImageViewer.ScreenDpi is set to the default value of 96.

When adding a new item to the viewer, the value of ImageViewerItem.Resolution will be checked. If the value is empty (or 0,0), then the viewer will try to obtain this value from this image data in platforms where this information can be obtained programmatically (such as Windows.Forms).

In platforms where the resolution cannot be obtained automatically (such as JavaScript), then it is the user's responsibility to set the value. For example, the LEADTOOLS HTML 5 Viewer Demo uses the LEADTOOLS REST services to obtain this value and set it for the item.

In either case, the user can then manually modify this value if desired.

Image Ownership

RasterImage and SvgDocument are both IDisposable objects. Eventually, some part of the code needs to dispose of these objects when they are no longer needed. This is controlled by using the ImageViewer.AutoDisposeImages property. In the examples above, the value of this property is to the default of true. Hence, the viewer disposes the image or SVG document when the item is removed. To prevent that, set the value of AutoDisposeImages to false.

Active Item

ImageViewer will always have an item denoted as the "Active" item. Access the item through the ImageViewer.ActiveItem property. This property cannot be set to null unless there are no more items in the viewer.

When an item is removed, the viewer will automatically check if it was the active item. If so, it will set the next closest item as the new active item.

The ActiveItem is important when using the viewer in a single item mode as described below.

Single Item Mode

Some applications, such as the Main Demo shipped with LEADTOOLS, does not require multiple items in the image viewer and will always have a single item that either has image data or does not have it.

For these type of applications, the image viewer provides shortcuts for all the properties and methods that would normally require accessing the ImageViewer.Items collection or modifying ImageViewerItem.

To achieve this, the image viewer layout must be set to ImageViewerSingleViewLayout and an empty item must be set in ImageViewer.Items. This item will be the ActiveItem, since the image viewer must have an active item at all times. This is precisely what happens when creating a new instance of ImageViewer using the default constructor, with the following code:

// Create a new image viewer instance using the default constructor 
ImageViewer imageViewer = new ImageViewer(); 
// Set some properties 
imageViewer.Dock = DockStyle.Fill; 
// Add it to the form 
this.Controls.Add(imageViewer); 
// Verify that we have a view layout, and it is of type single 
Debug.Assert(imageViewer.ViewLayout != null && imageViewer.ViewLayout is ImageViewerSingleViewLayout); 
// Verify that we have a single item 
Debug.Assert(imageViewer.Items.Count == 1); 
// Verify that we have an active item 
Debug.Assert(imageViewer.ActiveItem != null); 
// Load an image into it 
using (RasterCodecs codecs = new RasterCodecs()) 
   imageViewer.Image = codecs.Load(@"C:\LEADTOOLS22\Resources\Images\Ocr1.tif", 1); 
// Show the image size 
MessageBox.Show("ImageSize: " + imageViewer.ImageSize.ToString()); 

The ImageViewer.Image property is a short cut to ImageViewer.ActiveItem.Image. For more information, refer to Image Viewer Single Item Mode.

Note that all the members will return null (or default value) if the viewer does not have any items.

Additional Item Operations and Properties

The ImageViewerItem class also supports the following members:

See Also

Reference

Using ImageViewer

Using Image Viewer with Windows.Forms

Image Viewer Appearance

Image Viewer Bounds and Transform

Image Viewer Transformation

Image Viewer Layouts

Image Viewer Rendering

Image Viewer Scrolling

Image Viewer Interactive Modes

Image Viewer Other Operations

Image Viewer Single Item Mode

Image Viewer Virtualizer

Image Viewer Drag and Drop

Image Viewer Sync