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:

Member	Description
ImageViewerItems.Add	Adds a new item to the viewer
ImageViewerItems.Insert	Inserts at the specified index a new item to the viewer
ImageViewerItems.Remove	Removes an item from the viewer
ImageViewerItems.RemoveAt	Removes the item at the specified index from the viewer
ImageViewerItems.Clear	Delete all the items from the viewer
ImageViewerItems.Item	Gets or sets an item at the specified index
ImageViewerItems.Contains	Determines whether an item is in the viewer
ImageViewerItems.IndexOf	Gets the index of the specified item

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

Member	Description
ItemChanged	Occurs when an item has changed
ItemError	Occurs when an error occurred while setting the item image data
SelectedItemsChanged	Occurs when the number of values of selected items has changed

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

Member	Description
GetSelected	Returns the current selected items in the viewer
Select	Select items in the viewer
AddFromImage	Adds an item from a RasterImage object
InsertFromImage	Inserts an item at the specified index from a RasterImage object
AddFromImageUrl	Adds an item from a URL pointing to an image file
InsertFromImageUrl	Inserts an item at the specified index from a URL pointing to an image file
AddFromImageFile	Adds an item from an image file on disk
InsertFromImageFile	Inserts an item at the specified index from an image file on disk
UpdateImage	Replaces or sets the RasterImage object of an item
UpdateUrl	Repalces or sets the image data of an item from a URL pointing to an image file
AddFromSvgUrl	Adds an item from a URL pointing to an image or document file that supports loading as SVG
InsertFromSvgUrl	Inserts an item at the specified index from a URL pointing to an image or document file that supports loading as SVG
AddFromSvgFile	Adds an item from a disk file containing an image or document file that supports loading as SVG
InsertFromSvgFile	Inserts an item at the specified index from a disk file containing an image image or document file that supports loading as SVG
UpdateSvgDocument	Replaces or sets the SvgDocument object of an item

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 a SvgDocument object
From a URL containing raster or SVG image data
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:\Users\Public\Documents\LEADTOOLS Images\Ocr1.tif", 1);
            // Add it to the viewer
            imageViewer.Items.Add(item);

Or by letting 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:\Users\Public\Documents\LEADTOOLS Images\Ocr1.tif");
            // Add it to the viewer
            imageViewer.Items.Add(item);

You can also use the method of ImageViewerItems to add the items directly without creating an ImageViewerItem instance:


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

Or from a file directly without creating a RasterImage object:


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

Or from a URL


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

In the cases above, you can easily obtain the item added for further modification by using the return value 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 loading 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:\Users\Public\Documents\LEADTOOLS Images\Leadtools.pdf", 1, null) as SvgDocument;
            // Add it to the viewer
            imageViewer.Items.Add(item);

Similarly to using RasterImage, you can let the viewer 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:\Users\Public\Documents\LEADTOOLS 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:\Users\Public\Documents\LEADTOOLS 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 always recommended to disable the viewer from updating while multiple items are added (or removed, or updated). Doing so will ensure 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:\Users\Public\Documents\LEADTOOLS 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 sets 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:

Member	Description
ImageViewerItem.Size	The size of the whole item, including any margins, borders and padding
ImageViewerItem.ImageSize	The image size in pixels

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:

Value of ImageViewerItem.ImageSize	ImageViewerItem.Image or ImageViewerItem.SvgDocument	Description
LeadSize.Empty or 0,0	Available	The viewer will use automatically calculate the value from the image data (Image or SvgDocument) and set it in ImageViewerItem.ImageSize. The code snippets above rely on this auto-calculations.
LeadSize.Empty or 0,0	Not set	ImageViewerItem.ImageSize stays empty. This item will be invisible and will not participate in the layout calculation. The size can be set at a later time if desired to make the item visible.
Not empty	Available	The viewer will not calculate the value from the image data, instead, the value is used as is. The viewer will automatically stretch or shrink the image data when calculating the transformation or rendering to match the size.
Not empty	Not Available	The viewer will treat the item as it has image data with the specified size. It will use this value in the transformation calculation but will not render any image data. The ImageViewerVirtualizer uses this mode extensively to render a place holder of the actual image till the data is available. This mode can also be used to custom render image data.

Item Size

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

Value of ImageViewer.ItemSize	Value of ImageViewerItem.Size	Description
LeadSize.Empty or 0,0	LeadSize.Empty or 0,0	This is the default mode. The viewer will use the value of ImageViewer.ItemSize calculated above and set it in ImageViewerItem.Size. Hence, the item will have the same value for both and the image will occupy the full item area
Not empty	LeadSize.Empty or 0,0	The viewer will set the value of ImageViewer.ItemSize into ImageViewerItem.Size. All the items will have the same size and each image will be placed and rendered inside the item depending on their own ImageViewerItem.ImageSize values and alignment. This mode is useful when the viewer is used as an "image list" or "thumbnails browser".
LeadSize.Empty or 0,0	Not empty	The viewer will use the value of ImageViewerItem.Size as the size of the item. ImageViewerItem.ImageSize will not be used in this calculation and only to determine where to place and render the image inside the item.
Not empty	Not empty	The viewer will ignore ImageViewer.ItemSize and use ImageViewerItem.Size.

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's 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 A4 document image is 8.5 by 11 inches. Which could be 2550 by 3300 pixels if the image has a resolution of 300 by 300. Most document viewer applications will try to display this image in its original size. In other words, 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, you can 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 will produce 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's the user 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 is desired.

Image Ownership

RasterImage and SvgDocument are both IDisposable objects. Eventually, some part of the code need to dispose these objects when they are no longer needed. This is controlled by using the ImageViewer.AutoDisposeImages property. In the examples above, we left the value of this property 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", this can be accessed 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 and if so, will set the next closest item as the new active.

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

Single Item Mode

Some application 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 not.

For these type of application, the image viewer provides shortcuts for all the properties and method 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 you create a new instance of ImageViewer using the default constructor, 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:\Users\Public\Documents\LEADTOOLS 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 Operation and Properties

The ImageViewerItem class also supports the following members:

Member	Description
IsVisible	Controls the visibility of the item in the viewer. Invisible items will not be rendered nor participate in layout calculations
IsEnabled	Determines whether the item is enabled. Inactive items are rendered and participate in layout calculations but do not respond to interactive mode events
IsSelected	Determines whether the item is in a selected state. Selected items may be rendered differently than non-selected items
IsHovered	Determines whether the item is in a hovered state. Hovered items may be rendered differently
ClipImageToContent	Determines whether to restrict rendering of the image inside its item area if the image size or transformation result in display coordinates that lay outside the item boundary
ImageVerticalAlignment	Determines how the image is aligned vertically inside the item boundary
ImageHorizontalAlignment	Determines how the image is aligned horizontally inside the item boundary
Text	Text string associated with this item. Can be used to show a page number or file name or any other text data
TextVerticalAlignment	Determines how the text is aligned vertically inside the item boundary
TextHorizontalAlignment	Determines how the text is aligned horizontally inside the item boundary
Floater	The floater image of this item
FloaterTransform	Position, scale and rotation of the floater image relative to the image
FloaterOpacity	Controls the opacity of the floater. Can also be used to hide the floater completely
PageNumber	Item page number. Can be used to hold the original page number of the document being viewer
PageCount	Number of pages in the Image property
ImageRegionToFloater	Converts the region found in Image into a floater
CombineFloater	Merge the floater with the current image
Tag	User defined data

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