Overview of codecs architecture

In This Topic

Definitions:

Decoder - an object that performs decoding of images of certain format.
Encoder - an object that performs encoding of images of certain format.
Codec - an object that manages encoder and decoder for certain image format.

The SDK contains the open architecture of image codecs, which is used for obtaining information, encoding and decoding images of various formats (TIFF, PDF, BMP, etc).

All classes used for image encoding and decoding are located in Vintasoft.Imaging.Codecs namespace.

The following diagram illustrates the logical links among base classes of the codecs architecture:

Logical links among base classes of the codecs architecture

The basic classes, illustrated on the above diagram, are divided into four levels of abstraction:

The "codecs" level consists from AvailableCodecs, AvailableDecoders, AvailableEncoders,Codec and derived classes. AvailableCodecs, AvailableDecoders and AvailableEncoders classes provide information about available decoders and encoders as well as provide the ability to add and remove codecs. Codec and derived classes contain methods allowing to create encoder or decoder for specific image formats.
The "encoder/decoder" level consists from EncoderBase and DecoderBase classes and derived classes,which provide the unified access to the functions intended for obtaining information and image encoding/decoding.
The "image file" level consists from ImageFileBase<T> and derived classes and related classes. The classes, which are derived from ImageFileBase<T> and ImagePage classes, provide the full access to all features of image decoding/encoding and to the metadata of specific format.
ImageFileSource class is used by ImageFileBase<T> hierarchy classes for reading/writing binary data from an instance of System.IO.Stream object.
The "encoded data" level represents System.IO.Stream class, which contains image data encoded ina specific format (TIFF, PDF, BMP, etc).

1. "Codec" and "AvailableCodecs" classes

Static AvailableCodecs class contains information about available codecs as well as provides the ability to remove and add new codecs:

AvailableCodecs.Codecs property provides access to a list of available codecs, instances of classes derived from Codec class.
AvailableCodecs.AddCodec, AvailableCodecs.InsertCodec, AvailableCodecs.RemoveCodec methods allows to manipulate the list of AvailableCodecs.Codecs.
AvailableCodecs.IsCodecAvailable method allows to determine whether there is available codec with specified name.

The Codec class is base class for all codecs. The Codec class defines how to create decoder and encoder for images of specific format.
Codec class includes the following informative properties:

Codec.Name - codec name.
Codec.FileExtensions - defines the file extension associated with the codec.
Codec.CanCreateDecoder - determines whether the codec can create decoders using function Codec.CreateDecoder.
Codec.CanCreateEncoder - determines whether the codec can create encoders using function Codec.CreateEncoder.

New codec, derived from Codec class, always must implement at least the following methods:

Codec.CreateDecoder - creates an instance of class derived from DecoderBase class using constructor without parameters or using constructor which receives a stream containing encoded image data.
Codec.CreateEncoder - creates an instance of class derived from EncoderBase class using constructor without parameters.

Important: The static Codec.CreateStandardCodec method allows to create by name a "standard" codec for the following image file formats: Bmp, Docx, Emf, Gif, Icon, Jbig2, Jpeg, Jpeg2000, Pbm, Pdf, Png, Raw, Tga, Tiff, Webp, Wmf, Xlsx.

Here is C#/VB.NET code that demonstrates how to obtain information about available codecs and their characteristics:

/// <summary>
/// Shows detailed information about available codecs.
/// </summary>
public static void ShowAvailableCodecsInfo()
{
    foreach (Vintasoft.Imaging.Codecs.Codec codec in Vintasoft.Imaging.Codecs.AvailableCodecs.Codecs)
    {
        string codecInfo = "";
        if (codec.CanCreateDecoder && codec.CanCreateEncoder)
            codecInfo = "decoder, encoder";
        else if (codec.CanCreateDecoder)
            codecInfo = "decoder";
        else if (codec.CanCreateEncoder)
            codecInfo = "encoder";
        System.Console.WriteLine(string.Format("{0} codec ({1}):", codec.Name, codecInfo));
        System.Console.Write("  File extensions:");
        for (int i = 0; i < codec.FileExtensions.Length; i++)
        {
            System.Console.Write(string.Format(" *{0}", codec.FileExtensions[i].ToLowerInvariant()));
        }
        System.Console.WriteLine();
    }
}

/* This code example produces the following output:
    
Raw codec (decoder):
  File extensions: *.nef *.nrw *.cr2 *.crw *.dng
Tiff codec (decoder, encoder):
  File extensions: *.tif *.tiff
Gif codec (decoder, encoder):
  File extensions: *.gif
Png codec (decoder, encoder):
  File extensions: *.png
Jpeg codec (decoder, encoder):
  File extensions: *.jpg *.jpeg
Bmp codec (decoder, encoder):
  File extensions: *.bmp
Pdf codec (decoder, encoder):
  File extensions: *.pdf
Jbig2 codec (decoder, encoder):
  File extensions: *.jb2 *.jbig2
Jpeg2000 codec (decoder, encoder):
  File extensions: *.jp2 *.jpc *.j2k *.j2c
Dicom codec (decoder):
  File extensions: *.dcm *.dic *.acr
Docx codec (decoder):
  File extensions: *.docx
Wmf codec (decoder):
  File extensions: *.wmf
Emf codec (decoder):
  File extensions: *.emf
Icon codec (decoder):
  File extensions: *.ico *.cur
Jpeg-LS codec (decoder):
  File extensions: *.jls
Pcx codec (decoder, encoder):
  File extensions: *.pcx
  
 */

VB.NET

        ''' <summary>
        ''' Shows detailed information about available codecs.
        ''' </summary>
        Public Shared Sub ShowAvailableCodecsInfo()
            For Each codec As Vintasoft.Imaging.Codecs.Codec In Vintasoft.Imaging.Codecs.AvailableCodecs.Codecs
                Dim codecInfo As String = ""
                If codec.CanCreateDecoder AndAlso codec.CanCreateEncoder Then
                    codecInfo = "decoder, encoder"
                ElseIf codec.CanCreateDecoder Then
                    codecInfo = "decoder"
                ElseIf codec.CanCreateEncoder Then
                    codecInfo = "encoder"
                End If
                System.Console.WriteLine(String.Format("{0} codec ({1}):", codec.Name, codecInfo))
                System.Console.Write("  File extensions:")
                For i As Integer = 0 To codec.FileExtensions.Length - 1
                    System.Console.Write(String.Format(" *{0}", codec.FileExtensions(i).ToLowerInvariant()))
                Next
                System.Console.WriteLine()
            Next
        End Sub

        ' This code example produces the following output:
'
'        Raw codec (decoder):
'          File extensions: *.nef *.nrw *.cr2 *.crw *.dng
'        Tiff codec (decoder, encoder):
'          File extensions: *.tif *.tiff
'        Gif codec (decoder, encoder):
'          File extensions: *.gif
'        Png codec (decoder, encoder):
'          File extensions: *.png
'        Jpeg codec (decoder, encoder):
'          File extensions: *.jpg *.jpeg
'        Bmp codec (decoder, encoder):
'          File extensions: *.bmp
'        Pdf codec (decoder, encoder):
'          File extensions: *.pdf
'        Jbig2 codec (decoder, encoder):
'          File extensions: *.jb2 *.jbig2
'        Jpeg2000 codec (decoder, encoder):
'          File extensions: *.jp2 *.jpc *.j2k *.j2c
'        Dicom codec (decoder):
'          File extensions: *.dcm *.dic *.acr
'        Docx codec (decoder):
'          File extensions: *.docx
'        Wmf codec (decoder):
'          File extensions: *.wmf
'        Emf codec (decoder):
'          File extensions: *.emf
'        Icon codec (decoder):
'          File extensions: *.ico *.cur
'        Jpeg-LS codec (decoder):
'          File extensions: *.jls
'        Pcx codec (decoder, encoder):
'          File extensions: *.pcx
'
'

2. "DecoderBase" and "AvailableDecoders" classes

Static AvailableDecoders class contains information about available decoders and allows to:

Get decoder for specified stream, which contains encoded image data, using AvailableDecoders.CreateDecoder method.
Get names of available decoders using AvailableDecoders.DecoderNames property.
Check whether there is available decoder with specified name using AvailableDecoders.IsDecoderAvailable method.

VintasoftImage object uses AvailableDecoders.CreateDecoder method for choosing the decoder, which allows to decode image data from stream or file, which contains image data.

The DecoderBase class is base class for all decoders. The DecoderBase class defines the unified set of methods intended for obtaining metadata and image decoding:

DecoderBase.IsValidFormat - allows to determine whether the decoder can decode data from specified stream.
DecoderBase.PageCount - returns the count of pages in specified stream.
DecoderBase.GetImage - returns an image of specifed page.
DecoderBase.GetThumbnail - returns a thumbnail of specified page.
DecoderBase.GetImageInfo - allows to obtain image parameters (like size, resolution, pixel format, etc) of specified page.
DecoderBase.GetPageMetadata - returns metadata of specified page.

Here is C#/VB.NET code that demonstrates how to get the decoder for the specified stream and obtain information about all images encoded in that stream:

/// <summary>
/// Shows detailed information about pages of image stored in specified stream.
/// </summary>
public static void ShowInformationAboutPages(System.IO.Stream stream)
{
    Vintasoft.Imaging.Codecs.Decoders.DecoderBase decoder;
    try
    {
        // create appropriate decoder
        decoder = Vintasoft.Imaging.Codecs.Decoders.AvailableDecoders.CreateDecoder(stream);
    }
    catch (Vintasoft.Imaging.Codecs.Decoders.DecoderException ex)
    {
        System.Console.WriteLine(ex.Message);
        return;
    }

    if (decoder == null)
    {
        System.Console.WriteLine("Appropriate decoder was not found.");
        return;
    }

    // get the number of pages
    System.Console.WriteLine(string.Format("Stream contains {0} page(s).", decoder.PageCount));
    for (int i = 0; i < decoder.PageCount; i++)
    {
        // get the information about the page
        Vintasoft.Imaging.Codecs.Decoders.ImageInfo pageImageInfo = decoder.GetImageInfo(i);

        System.Console.WriteLine();

        // get general image parameters

        System.Console.WriteLine(string.Format("Page {0}:", i + 1));
        System.Console.WriteLine(string.Format("  Image dimensions: {0}x{1} pixels", pageImageInfo.Width, pageImageInfo.Height));
        System.Console.WriteLine(string.Format("  Image resolution: {0}x{1} dpi",
            System.Math.Round(pageImageInfo.Resolution.Horizontal), System.Math.Round(pageImageInfo.Resolution.Vertical)));
        System.Console.WriteLine(string.Format("  Image bit depth: {0}", pageImageInfo.BitsPerPixel));
        System.Console.WriteLine(string.Format("  Image pixel format: {0}", pageImageInfo.PixelFormat));

        // get information about palette

        int paletteColorCount = pageImageInfo.Palette.ColorCount;
        if (paletteColorCount > 0)
            System.Console.WriteLine(string.Format("  Image has a palette with {0} colors", paletteColorCount));
        else
            System.Console.WriteLine(string.Format("  Image has no palette"));
        System.Console.WriteLine();
    }
}

VB.NET

''' <summary>
''' Shows detailed information about pages of image stored in specified stream.
''' </summary>
Public Shared Sub ShowInformationAboutPages(stream As System.IO.Stream)
    Dim decoder As Vintasoft.Imaging.Codecs.Decoders.DecoderBase
    Try
        ' create appropriate decoder
        decoder = Vintasoft.Imaging.Codecs.Decoders.AvailableDecoders.CreateDecoder(stream)
    Catch ex As Vintasoft.Imaging.Codecs.Decoders.DecoderException
        System.Console.WriteLine(ex.Message)
        Return
    End Try

    If decoder Is Nothing Then
        System.Console.WriteLine("Appropriate decoder was not found.")
        Return
    End If

    ' get the number of pages
    System.Console.WriteLine(String.Format("Stream contains {0} page(s).", decoder.PageCount))
    For i As Integer = 0 To decoder.PageCount - 1
        ' get the information about the page
        Dim pageImageInfo As Vintasoft.Imaging.Codecs.Decoders.ImageInfo = decoder.GetImageInfo(i)

        System.Console.WriteLine()

        ' get general image parameters

        System.Console.WriteLine(String.Format("Page {0}:", i + 1))
        System.Console.WriteLine(String.Format("  Image dimensions: {0}x{1} pixels", pageImageInfo.Width, pageImageInfo.Height))
        System.Console.WriteLine(String.Format("  Image resolution: {0}x{1} dpi", System.Math.Round(pageImageInfo.Resolution.Horizontal), System.Math.Round(pageImageInfo.Resolution.Vertical)))
        System.Console.WriteLine(String.Format("  Image bit depth: {0}", pageImageInfo.BitsPerPixel))
        System.Console.WriteLine(String.Format("  Image pixel format: {0}", pageImageInfo.PixelFormat))

        ' get information about palette

        Dim paletteColorCount As Integer = pageImageInfo.Palette.ColorCount
        If paletteColorCount > 0 Then
            System.Console.WriteLine(String.Format("  Image has a palette with {0} colors", paletteColorCount))
        Else
            System.Console.WriteLine(String.Format("  Image has no palette"))
        End If
        System.Console.WriteLine()
    Next
End Sub

3. "EncoderBase", "MultipageEncoderBase" and "AvailableEncoders" classes

Static AvailableEncoders class contains information about available encoders and allows to:

Get new encoder by file extension using AvailableEncoders.CreateEncoder, AvailableEncoders.CreateMultipageEncoder methods.
Get new encoder by encoder's name using AvailableEncoders.CreateEncoderByName method.
Get names of available encoders using AvailableEncoders.EncoderNames property.
Check whether there is available encoder with certain name using AvailableEncoders.IsEncoderAvailable method.

VintasoftImage and ImageCollection objects use AvailableEncoders.CreateEncoder method to choose the encoder by name of file to be encoded.

The EncoderBase class is base class for all encoders. The EncoderBase class defines unified set of methods intended for image encoding into single-page image format (PNG, BMP, JPEG, JPEG2000):

EncoderBase.SaveImage - performs encoding of specified VintasoftImage object into specified stream.
EncoderBase.GetEncodedImageInfo - allows to obtain information about image after encoding without real encoding of image.

The MultipageEncoderBase class is derived from EncoderBase and defines unified set of methods intended for encoding the image collection into multi-page image format (TIFF, PDF, GIF, JBIG2):

MultipageEncoderBase.SaveImages - performs encoding of VintasoftImage object collection into specified stream.
MultipageEncoderBase.CreateNewFile - allows to determine that image file must be cleared before encoding new images.

Here is C#/VB.NET code that demonstrates how to choose an encoder for certain file and perform saving of image collection into the file:

/// <summary>
/// Gets an encoder by the filename extension,
/// changes settings of the encoder and
/// saves an image collection to a file using encoder.
/// </summary>
public static void ChangeEncoderSettingsAndSave(Vintasoft.Imaging.ImageCollection images, string filename)
{
    // get an encoder by the filename extension
    Vintasoft.Imaging.Codecs.Encoders.EncoderBase encoder =
        Vintasoft.Imaging.Codecs.Encoders.AvailableEncoders.CreateEncoder(filename);
    // if encoder was not found
    if (encoder == null)
    {
        throw new System.Exception("Encoder is not found for specified file extension.");
    }
    // if encoder is TIFF
    if (encoder is Vintasoft.Imaging.Codecs.Encoders.TiffEncoder)
    {
        // specify that encoded image must be divided into tiles with size 512x512
        (encoder as Vintasoft.Imaging.Codecs.Encoders.TiffEncoder).Settings.UseTiles = true;
        (encoder as Vintasoft.Imaging.Codecs.Encoders.TiffEncoder).Settings.TileSize = new System.Drawing.Size(512, 512);
    }

    // create file
    using (System.IO.Stream stream = new System.IO.FileStream(filename,
        System.IO.FileMode.Create, System.IO.FileAccess.ReadWrite))
    {
        // if encoder is multipage
        if (encoder is Vintasoft.Imaging.Codecs.Encoders.MultipageEncoderBase)
        {
            // save all images
            (encoder as Vintasoft.Imaging.Codecs.Encoders.MultipageEncoderBase).SaveImages(images, stream);
        }
        else
        {
            // check if there is exactly 1 image
            if (images.Count != 1)
                throw new System.Exception("Single-page encoder cannot be used for saving multiple images.");

            encoder.SaveImage(images[0], stream);
        }
    }
}

VB.NET

''' <summary>
''' Gets an encoder by the filename extension,
''' changes settings of the encoder and
''' saves an image collection to a file using encoder.
''' </summary>
Public Shared Sub ChangeEncoderSettingsAndSave(images As Vintasoft.Imaging.ImageCollection, filename As String)
    ' get an encoder by the filename extension
    Dim encoder As Vintasoft.Imaging.Codecs.Encoders.EncoderBase = Vintasoft.Imaging.Codecs.Encoders.AvailableEncoders.CreateEncoder(filename)
    ' if encoder was not found
    If encoder Is Nothing Then
        Throw New System.Exception("Encoder is not found for specified file extension.")
    End If
    ' if encoder is TIFF
    If TypeOf encoder Is Vintasoft.Imaging.Codecs.Encoders.TiffEncoder Then
        ' specify that encoded image must be divided into tiles with size 512x512
        TryCast(encoder, Vintasoft.Imaging.Codecs.Encoders.TiffEncoder).Settings.UseTiles = True
        TryCast(encoder, Vintasoft.Imaging.Codecs.Encoders.TiffEncoder).Settings.TileSize = New System.Drawing.Size(512, 512)
    End If

    ' create file
    Using stream As System.IO.Stream = New System.IO.FileStream(filename, System.IO.FileMode.Create, System.IO.FileAccess.ReadWrite)
        ' if encoder is multipage
        If TypeOf encoder Is Vintasoft.Imaging.Codecs.Encoders.MultipageEncoderBase Then
            ' save all images
            TryCast(encoder, Vintasoft.Imaging.Codecs.Encoders.MultipageEncoderBase).SaveImages(images, stream)
        Else
            ' check if there is exactly 1 image
            If images.Count <> 1 Then
                Throw New System.Exception("Single-page encoder cannot be used for saving multiple images.")
            End If

            encoder.SaveImage(images(0), stream)
        End If
    End Using
End Sub

4. Image file hierarchy

ImageFile hierarchy provides a set of classes for parsing, decoding and encoding image files.

The following diagram illustrates the logical links among basic classes of ImageFile architecture:

Logical links among basic classes of ImageFile architecture

4.1. Image file

ImageFileBase<T> class is a base class for:

abstract SinglePageImageFile<T> class, which is used for creating single-page image files (BmpFile, PngFile, JpegFile, Jpeg2000File, RawImageFile)
abstract ImageFile<TPage, TPageCollection> class, which is used for creating multi-page image files (TiffFile, GifFile, Jbig2File, IconFile)

The classes, which are derived from ImageFileBase<T>, provide access to a collection of file pages (or a page in case of single-page format) and general information about the file. They also implement functions of parsing, saving changes, saving to new source and packing the file.

4.2. Image page

Abstract ImagePage class defines methods, which allow to obtain information about encoded image (height, width, palette, resolution, etc) and encode image.
Classes TiffPage, PngPage, BmpPage, DibPage, GifPage, IconPage, JpegPage, Jpeg2000Page, Jbig2Page, RawImagePageBase, which are derived from ImagePage class, also provides additional information about image: color space, compression, thumbnail and other format specific details.

4.3. Image file block

Each image file consists from file blocks. An abstract ImageFileBlock class describes a data block in file.
All file blocks have the following common attributes:

block length
block offset
source

Block can be virtual (ImageFileBlock.IsVirtual, i.e. created in memory without link to the real source (ImageFileSource). Virtual blocks appear when new file is created or new blocks are added to existing file. Blocks become real after saving the file to the source.
The overriden abstract method ImageFileBlock.Parse allows to implement the parsing algorithm for the specific block. The overriden abstract method ImageFileBlock.Write allows to implement the writing of encoded data into the source.

4.4. Image file source

ImageFileSource class allows to read/write data from/to the source. The class implements a wide range of data read/write functions for different data formats: Int16, Uint16, Int32, UInt32, Int64, UInt64, Char, Bool, Single, Double, Byte, Byte[]. The ImageFileSource class implements read/write operations in little-endian format. The BigEndianImageSource class implements read/write operations in big-endian format.

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