CSJ2K - A Managed and Portable JPEG2000 Codec

Copyright (c) 1999-2000 JJ2000 Partners; original C# port (c) 2007-2012 Jason S. Clary; C# encoding and adaptation to Portable Class Library with platform specific support (c) 2013-2016 Anders Gustafsson, Cureos AB

Licensed and distributable under the terms of the BSD license

NOTE! The following information applies to the upcoming version 2.0 of CSJ2K. Please consult commit associated with release 0.9.1 for details about 0.9.x versions of CSJ2K.

Summary

This is a Portable Class Library adaptation of CSJ2K, which provides JPEG 2000 decoding and encoding functionality to .NET based platforms. CSJ2K is by itself a C# port of the Java package jj2000, version 5.1. This Portable Class Library adaptation of CSJ2K makes it possible to implement JPEG decoding and encoding on the following platforms:

• Windows Universal Platform (8.1 and 10)
• Windows Phone Silverlight version 8 and higher
• Silverlight version 5
• .NET Framework version 4 and higher
• Xamarin iOS
• Xamarin Android

A Class Library targeting .NET Core is also included, targeting .NET Standard 1.0.

The code is still applicable to .NET 3.5 and later as well; a .NET 3.5 dedicated class library is maintained here for reference.

Along with the CSJ2K Portable Class Library there are also platform specific replacement libraries for bitmap processing and file handling. In particular, the .NET Framework library implements bitmap processing for WriteableBitmap, thus facilitating JPEG 2000 decoding in WPF based applications.

Included are very basic Universal Windows 8.1, WPF, Windows Phone 8 Silverlight, Silverlight 5, Xamarin Android and Xamarin iOS test applications for reading and displaying JPEG 2000 files.

Installation

Apart from building the relevant class libraries from source, pre-built packages for the supported platforms can also be obtained via NuGet.

Usage

The Portable Class Library provides interfaces for image rendering, file I/O and logging.

On .NET, both System.Drawing.Bitmap and WriteableBitmap images can be managed, but not simultaneously. By default, WriteableBitmap is managed. To work with Bitmap images instead, register the corresponding image creator:

BitmapImageCreator.Register();

To switch back to WriteableBitmap:

WriteableBitmapCreator.Register();

On other platforms, only one image manager is available and automatically selected.

Decoding

To decode a JPEG 2000 encoded image, call one of the following methods:

public class J2kImage
{
	public static PortableImage FromStream(Stream, ParameterList = null);
	public static PortableImage FromBytes(byte[], ParameterList = null);
	public static PortableImage FromFile(string, ParameterList = null);
}

J2kImage.FromFile(string) is not sufficiently implemented for Silverlight and Windows Phone.

The returned PortableImage offers a "cast" method As<T>() to obtain an image in the type relevant for the platform. When using the BitmapImageCreator on .NET, a cast to Bitmap would suffice:

var bitmap = decodedImage.As<Bitmap>();

On platforms implementing WriteableBitmap, use:

var wbm = decodedImage.As<WriteableBitmap>();

On Android, use:

var bitmap = decodedImage.As<Android.Graphics.Bitmap>();

On iOS, depending on context, use:

var image = decodedImage.As<CGImage>();
var image = decodedImage.As<CIImage>();
var image = decodedImage.As<UIImage>();

Encoding

To encode an image, the following overloads are available:

public class J2kImage
{
	public static byte[] ToBytes(object, ParameterList = null);
	public static byte[] ToBytes(BlkImgDataSrc, ParameterList = null);
}

The first overload takes an platform-specific image object. This is still works-in-progress, but a partial implementation is available for System.Drawing.Bitmap objects on .NET Desktop.

The second overload takes an CSJ2K specific object implementing the BlkImgDataSrc interface. When Portable Graymap (PGM), Portable Pixelmap (PPM) or JPEG2000 conformance testing format (PGX) objects are available as Streams, it is possible to create BlkImgDataSrc objects using either of the following methods:

J2kImage.CreateEncodableSource(Stream);
J2kImage.CreateEncodableSource(IList<Stream>);

For PGM and PPM images, you would normally use the single Stream overload, whereas for PGX images, you may enter one Stream object per color component.

Links

• CSJ2K web site on Codeplex
• Guide to the practical implementation of JPEG2000