MSDN Magazine - April 2008 - (Page 115)

Windows Imaging Component Basics KENNY KERR T he Microsoft® Windows® Imaging Component (WIC) is an extensible framework for encoding, decoding, and manipulating images. Originally designed for Windows Vista® and Windows Presentation Foundation (WPF), today WIC not only ships with Windows Vista and the Microsoft .NET Framework 3.0 and later, but it is also available as a download for Windows XP and Windows Server® 2003 for use in native applications. One of several powerful native frameworks that power WPF, WIC in this context is the framework used in the implementation of the System.Windows.Media.Imaging namespace. It is, however, also ideally suited for native applications written in C++ because it provides a simple-yet-powerful API exposed through a set of COM interfaces. WIC supports different image formats using an extensible set of imaging codecs. Each codec supports a different image format and typically provides both an encoder and decoder. WIC includes a set of built-in codecs for virtually all of the major image formats including PNG, JPEG, GIF, TIFF, HD Photo (HDP), ICO, and of course the Windows BMP. HDP is the only format you may not have heard about. It was originally called Windows Media Photo and was developed in conjunction with Windows Vista to overcome some of the limitations with existing formats and provide better performance and higher image quality. For more information on HDP, check out the specification at microsoft.com/whdc/xps/wmphoto.mspx. Fortunately, WIC provides great support for this new image format, so applications don’t have to know the specifics of the formats to use them. This month I’ll show you how to use WIC to encode and decode different image formats and a few things in between. Next time I’ll explore some of the more advanced features and show you how to extend WIC with your own imaging codecs. Figure 1 CLSIDs for Built-In WIC Codecs Format BMP PNG ICO JPEG GIF TIFF HDP Decoder CLSID_WICBmpDecoder CLSID_WICPngDecoder CLSID_WICIcoDecoder CLSID_WICJpegDecoder CLSID_WICGifDecoder CLSID_WICTiffDecoder CLSID_WICWmpDecoder Encoder CLSID_WICBmpEncoder CLSID_WICPngEncoder Not available CLSID_WICJpegEncoder CLSID_WICGifEncoder CLSID_WICTiffEncoder CLSID_WICWmpEncoder #include #include #pragma comment(lib, “WindowsCodecs.lib”) Since the WIC API consists primarily of COM interfaces, I use the Active Template Library (ATL) CComPtr class to handle the creation and management of the interface pointers. If you would like to do the same, you’ll need to also include the atlbase.h header file that defines the CComPtr template class: #include The WIC API also uses the COM library, so the CoInitializeEx function must be called on any thread that will use the API. Finally, the WIC API makes use of HRESULTs to describe errors. The samples in this article use the HR macro to clearly identify where methods return an HRESULT that needs to be checked. You can replace this with your own error-handling strategy—whether that is throwing an exception or returning the HRESULT yourself. Decoding Images Getting Started The WIC API consists of COM interfaces, functions, structures, and error codes, as well as GUIDs identifying various codecs, containers, and formats. All of the declarations you will need are included in the wincodec.h and wincodecsdk.h header files that are provided as part of the Windows SDK (and included with Visual Studio® 2008). It will also be necessary for you to link to the WindowsCodecs.lib library, which provides the various definitions you may need. You can add the following to your project’s precompiled header to make it all available: Decoders are represented by the IWICBitmapDecoder interface. WIC provides a few ways to create a decoder object, but at a minimum you can simply use a particular decoder’s CLSID to create an instance. The following example creates a decoder for a TIFF image: CComPtr decoder; HR(decoder.CoCreateInstance(CLSID_WICTiffDecoder)); Figure 1 lists the codecs included with WIC and the CLSIDs you can use to create the different decoders. Once the decoder is created, it needs to be initialized with a stream containing the pixels and optional metadata in a format understood by the decoder: CComPtr stream; // Create stream object here april2008 115 http://microsoft.com/whdc/xps/wmphoto.mspx

Table of Contents Feed for the Digital Edition of MSDN Magazine - April 2008

MSDN Magazine - April 2008 Contents Toolbox CLR Inside Out Basic Instincts Cutting Edge Foundations Test Run Service Station Windows with C++ Going Places { End Bracket }

MSDN Magazine - April 2008

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