Advanced functionality for image decoding

In This Topic

SDK includes the following interfaces for optimal decoding of image data:

IRasterGridDecoder - the interface can be implemented in raster image decoder, which can use the image grid with scaling for decoding of image.
ILineInterlacedDecoder - the interface can be implemented in raster image decoder, which can effectively skip one or more image lines while decoding a part of image.
ISimpleLineInterlacedDecoder - the interface can be implemented in raster image decoder, which can effectively skip one or more image lines while decoding the whole image.
IVectorDecoder - the interface can be implemented in vector image decoder.

ImageRenderer class decodes a part or a scaled part of image by the most optimal way and without loading the whole image into memory if decoder implements one or several of the following interfaces: IRasterGridDecoder, ILineInterlacedDecoder, ISimpleLineInterlacedDecoder, IVectorDecoder.

Important! It is recommended to use the ImageRenderer class for solving the following tasks:

get any part of image in specified scale synchronously and asynchronously
render image progressively
render image or a part of image in several threads

ImageViewer and WpfImageViewer classes can load only necessary part of image when image is displayed in image viewer if decoder implements one or several of the following interfaces: IRasterGridDecoder, ILineInterlacedDecoder, ISimpleLineInterlacedDecoder, IVectorDecoder. This functionality can be enabled/disabled using the ImageViewer.RenderingRequirements and WpfImageViewerBase.RenderingRequirements properties.

ImageViewer and WpfImageViewer classes can load image in image viewer progressively if decoder implements the IVectorDecoder interface. This functionality can be enabled/disabled using the ImageViewer.IntermediateImagePreviewInterval and WpfImageViewer.IntermediateImagePreviewInterval properties.

ThumbnailViewer and WpfThumbnailViewer classes can render image thumbnail without loading the whole image into memory if decoder implements one or several of the following interfaces: IRasterGridDecoder, ILineInterlacedDecoder, ISimpleLineInterlacedDecoder, IVectorDecoder.

Here is C#/VB.NET code that demonstrates how to render the specified image region in specified scale using ImageRenderer class:

/// <summary>
/// Returns the scaled image region.
/// </summary>
/// <param name="image">The source image.</param>
/// <param name="rect">The image region on source image, which should be rendered.</param>
/// <param name="scale">The scale factor, which should be applied to the image region.</param>
/// <returns>The scaled image region.</returns>
public static Vintasoft.Imaging.VintasoftImage RenderScaledImageRegion(
    Vintasoft.Imaging.VintasoftImage image,
    System.Drawing.Rectangle rect,
    float scale)
{
    // create the image renderer
    using (Vintasoft.Imaging.ImageRendering.ImageRenderer renderer = 
        new Vintasoft.Imaging.ImageRendering.ImageRenderer(image))
    {
        // create the rendering task
        Vintasoft.Imaging.ImageRendering.ImageRenderingTask task = 
            Vintasoft.Imaging.ImageRendering.ImageRenderingTask.CreateImageRegion(rect, scale);
        // execute the rendering
        return renderer.ExecuteRendering(task);
    }
}

VB.NET

''' <summary>
''' Returns the scaled image region.
''' </summary>
''' <param name="image">The source image.</param>
''' <param name="rect">The image region on source image, which should be rendered.</param>
''' <param name="scale">The scale factor, which should be applied to the image region.</param>
''' <returns>The scaled image region.</returns>
Public Shared Function RenderScaledImageRegion(image As Vintasoft.Imaging.VintasoftImage, rect As System.Drawing.Rectangle, scale As Single) As Vintasoft.Imaging.VintasoftImage
    ' create the image renderer
    Using renderer As New Vintasoft.Imaging.ImageRendering.ImageRenderer(image)
        ' create the rendering task
        Dim task As Vintasoft.Imaging.ImageRendering.ImageRenderingTask = Vintasoft.Imaging.ImageRendering.ImageRenderingTask.CreateImageRegion(rect, scale)
        ' execute the rendering
        Return renderer.ExecuteRendering(task)
    End Using
End Function

1. Decode part or scaled part of raster image

The following interfaces are responsible for decoding of raster image:

IRasterGridDecoder is implemented by Jpeg2000Decoder, TiffDecoder, JpegDecoder decoders
ILineInterlacedDecoder is implemented by BmpDecoder decoder
ISimpleLineInterlacedDecoder is implemented by PngDecoder decoder

IRasterGridDecoder interface can be implemented in raster image decoder, which can use the image grid with scaling for decoding of image. The interface provides the wide abilities to get a part or whole image in necessary scale and without the need to decode the whole image. The class, which implements this interface, should support the following methods:

IRasterGridDecoder.GetImageRectGrid - returns an image grid as array of rectangles
IRasterGridDecoder.GetImageRectScales - returns an array of scale factors for rectangles of image grid
IRasterGridDecoder.GetImageRect - returns scaled or unscaled rectangle of raster image
IRasterGridDecoder.GetImageRegion - returns scaled or unscaled region of raster image
IRasterGridDecoder.CanReadImageRegion - determines that decoder can decode a region of the image
IRasterGridDecoder.CanUseProgressiveDecoding - determines that decoder can progressively decode an image

ILineInterlacedDecoder interface can be implemented in raster image decoder, which can effectively skip one or more image lines while decoding a part of image. The class, which implements this interface, must support ILineInterlacedDecoder.GetImage method, which performs the rendering of image with specified interlace decoding settings (InterlaceSettings).

InterlaceSettings class defines the following interlace decoding settings:

the rectangle which will be decoded
the step, used for interlaced decoding of image lines.

ISimpleLineInterlacedDecoder interface can be implemented in raster image decoder, which can effectively skip one or more image lines while decoding the whole image. The decoder, which implements this interface, must support the ISimpleLineInterlacedDecoder.GetImage method, which performs rendering of image with specified interlace step.

Here is C#/VB.NET code that demonstrates how to render a part of JPEG2000 image reduced 4 times:

/// <summary>
/// Returns a 4 times downscaled image of left-top rectangle of JPEG2000 image.
/// </summary>
public static Vintasoft.Imaging.VintasoftImage GetJpeg2000RectangleDownscaled4(string filename)
{
    using (System.IO.Stream stream =
        new System.IO.FileStream(filename, System.IO.FileMode.Open, System.IO.FileAccess.Read))
    {
        using (Vintasoft.Imaging.Codecs.Decoders.Jpeg2000Decoder decoder =
            new Vintasoft.Imaging.Codecs.Decoders.Jpeg2000Decoder(stream))
        {
            // check available scales
            int[] scales = decoder.GetImageRectScales(0, decoder.GetDefaultDecodingSettings(0));
            for (int i = 0; i < scales.Length; i++)
            {
                if (scales[i] == 4)
                {
                    // get top-left rectangle of raster grid with scale 4
                    return decoder.GetImageRect(0, 0, 4, null, null, null);
                }
            }

            throw new System.Exception("Scale 4 is not available for specified JPEG2000 file.");
        }
    }
}

VB.NET

''' <summary>
''' Returns a 4 times downscaled image of left-top rectangle of JPEG2000 image.
''' </summary>
Public Shared Function GetJpeg2000RectangleDownscaled4(filename As String) As Vintasoft.Imaging.VintasoftImage
    Using stream As System.IO.Stream = New System.IO.FileStream(filename, System.IO.FileMode.Open, System.IO.FileAccess.Read)
        Using decoder As New Vintasoft.Imaging.Codecs.Decoders.Jpeg2000Decoder(stream)
            ' check available scales
            Dim scales As Integer() = decoder.GetImageRectScales(0, decoder.GetDefaultDecodingSettings(0))
            For i As Integer = 0 To scales.Length - 1
                If scales(i) = 4 Then
                    ' get top-left rectangle of raster grid with scale 4
                    Return decoder.GetImageRect(0, 0, 4, Nothing, Nothing, Nothing)
                End If
            Next

            Throw New System.Exception("Scale 4 is not available for specified JPEG2000 file.")
        End Using
    End Using
End Function

2. Render a region of vector image

IVectorDecoder interface is responsible for rendering some part of vector image. IVectorDecoder interface can be implemented in vector image decoder and is implemented by PdfDecoder, DocxDecoder and XlsxDecoder classes. IVectorDecoder interface defines the single IVectorDecoder.GetImage method, which has the following parameters:

pageIndex - index of page
rect - the desired rectangle in source image coordinates
scale - the desired scale
decodingSettings - decoding settings
renderingSettings - rendering settings
imageRenderingProgress - delegate of rendering progress
intermediateImageRequest - delegate using which can be organized the rendering of intermediate states of image.

Here is C#/VB.NET code that demonstrates how to obtain a part of PDF document page:

/// <summary>
/// Returns an enlarged image of the central region of PDF page.
/// </summary>
public static Vintasoft.Imaging.VintasoftImage GetEnlargedImageOfPdfPageRegion(string filename, int pageIndex)
{
    using (System.IO.Stream stream =
        new System.IO.FileStream(filename, System.IO.FileMode.Open, System.IO.FileAccess.Read))
    {
        using (Vintasoft.Imaging.Codecs.Decoders.PdfDecoder decoder =
            new Vintasoft.Imaging.Codecs.Decoders.PdfDecoder(stream))
        {
            // settings for page rendering
            Vintasoft.Imaging.Codecs.Decoders.RenderingSettings renderingSettings =
                Vintasoft.Imaging.Codecs.Decoders.RenderingSettings.Empty;
            // get page info
            Vintasoft.Imaging.Codecs.Decoders.ImageInfo pageInfo = decoder.GetImageInfo(pageIndex, renderingSettings, null);

            // determine region on page
            float x = 3f * pageInfo.Width / 8f;
            float y = 3f * pageInfo.Height / 8f;
            float width = pageInfo.Width / 4f;
            float height = pageInfo.Height / 4f;
            System.Drawing.RectangleF rect = new System.Drawing.RectangleF(x, y, width, height);

            // get the central region with size of 1/4 page and scale 4
            return decoder.GetImage(pageIndex, rect, 4f, null, renderingSettings, null, null);
        }
    }
}

VB.NET

''' <summary>
''' Returns an enlarged image of the central region of PDF page.
''' </summary>
Public Shared Function GetEnlargedImageOfPdfPageRegion(filename As String, pageIndex As Integer) As Vintasoft.Imaging.VintasoftImage
    Using stream As System.IO.Stream = New System.IO.FileStream(filename, System.IO.FileMode.Open, System.IO.FileAccess.Read)
        Using decoder As New Vintasoft.Imaging.Codecs.Decoders.PdfDecoder(stream)
            ' settings for page rendering
            Dim renderingSettings As Vintasoft.Imaging.Codecs.Decoders.RenderingSettings = Vintasoft.Imaging.Codecs.Decoders.RenderingSettings.Empty
            ' get page info
            Dim pageInfo As Vintasoft.Imaging.Codecs.Decoders.ImageInfo = decoder.GetImageInfo(pageIndex, renderingSettings, Nothing)

            ' determine region on page
            Dim x As Single = 3F * pageInfo.Width / 8F
            Dim y As Single = 3F * pageInfo.Height / 8F
            Dim width As Single = pageInfo.Width / 4F
            Dim height As Single = pageInfo.Height / 4F
            Dim rect As New System.Drawing.RectangleF(x, y, width, height)

            ' get the central region with size of 1/4 page and scale 4
            Return decoder.GetImage(pageIndex, rect, 4F, Nothing, renderingSettings, Nothing, _
                Nothing)
        End Using
    End Using
End Function

2.1. Obtain intermediate images during image rendering

The ImageViewer, WpfImageViewer and ImageRenderingTask classes allow to obtain intermediate images during rendering of vector image. This feature makes the rendering process of complex vector images visually faster. The interval for displaying the intermediate images can be set using the following properties:

For correct work of the above mechanism the vector decoder must block image, which being rendered, with non-exclusive write rights.

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