Sustainability of Digital Formats
 Planning for Library of Congress Collections

Format for continuous-tone still images that supports a wide range of features including:

• Multiple color formats for display or print
• Fixed or floating point, high-dynamic-range image encoding
• Lossless or high-quality lossy compression
• Efficient decoding for multiple resolutions and sub-regions
• Minimal overhead for format conversion or transformations during decoding

The developer states that the format delivers "a lightweight, high-performance algorithm with a small memory footprint that enables practical, in-device encoding and decoding."

Support for HD Photo is provided by the Windows Imaging Component (WIC) installable codec architecture and the Windows Presentation Foundation (WPF; concerned in part with user interfaces) developed for the Windows Vista operating system. Microsoft states that Vista represents the integration of imaging at the operating system level, reducing the level of activity required of specific applications.

In a July 31, 2007, press release, Microsoft Corp. announced the decision by the Joint Photographic Expert Group (JPEG) to introduce a new work item for the standardization of HD Photo which, if approved, would lead to a format tentatively titled "JPEG XR."

Licensing applies to applications that create or display images, not to the images themselves. A Microsoft Web page consulted in August 2006 and no longer available in January 2007 (http://www.microsoft.com/windows/windowsmedia/licensing/wmphoto.aspx) stated, "Under most conditions, Windows Media Photo technology is available free of charge; royalties are associated only with specific licensing conditions."

According to the Wikipedia article "HD Photo" (consulted February 6, 2008), "A Microsoft representative stated in a January 2007 interview that in order to encourage the adoption and use of HD Photo, the specification is made available under the Microsoft Open Specification Promise, which asserts that Microsoft offers the specification for free, and will not file suit on the patented technology, and that open-source software can therefore make use of the format. However, as of Microsoft's December 4, 2007 update, HD Photo is still not among the technologies that Microsoft has listed as being covered by the Open Specification Promise."

WMP_1_0 uses a "TIFF-like" file container to store image data in a table of Image File Directory (IFD) tags, using tag numbers from TIFF's baseline, extended, and "private" sets. Examples of tags drawn from extended and private TIFF sets: ICCProfile (34675), XMPMetadata (700), and EXIFMetadata (34665). For an overview of tags, including a listing of WMP_1_0 tags, see Tags for TIFF and Related Specifications.

The large number of possible image encodings are identified by means of GUIDs specified by Microsoft. (This contrasts with an approach based upon the placement of data in a set of tags for such features as bits per pixel, photometric interpretation, and so on.)

Regarding compression: The Wikipedia article "HD Photo" offers a good overview of the format. The following summation is from the January 2007 version of this article; a more detailed version was available in February 2008. The 2007 summation stated that HD Photo "uses a reversible color space conversion, a reversible lapped biorthogonal transform and a non-arithmetic entropy encoding scheme, which is very efficient in preserving high frequency image data. This makes the algorithm retain a higher image quality at high compression ratios. The transform operation needs 3 multiply and add operations and 7 add or shift operations at the highest quality level and in the highest performance mode, 1 multiply and add operation and 4 add or shifts are required per pixel, giving the codec a high performance. [HD Photo] processes images in 16x16 macroblocks."

Regarding digital rights management: In a blog consulted in August 2006, HD Photo Program Manager Bill Crow commented:

• Windows Media DRM is ideal for publishing audio and video, but is really not that useful for still photography. Most commercial scenarios for digital photos require that the customer receive direct access to the image, which basically defeats the approach used by Windows Media DRM (where the goal is to protect the content all the way to the glass or speakers). Also, Windows Media DRM is designed for a "few to many" publishing model; the DRM license gerneration technology does not easily allow anyone to generate their own DRM licenses.
• While we are looking at DRM for photos for possible support in the future, the initial implementation was deliberately been designed to be simple, lightweight and easy for partners to implement directly in devices. That said, you can currently use Windows Document Rights Management for very effective management of rights access to digital photos.
• We're investigating more comprehensive solutions to manage digital photo access rights, copyright protection and provenance guarantees as features for future versions of Windows Media Photo.

Other notes:Bill Crow's own blog is informative; here are some excerpts collected in August 2006:

• Our current encoder tools include a choice between the sample applications that are part of the Windows Media Photo Device Porting Kit (DPK) or an encoder utility based on the Windows Imaging Components (WIC) interfaces that we developed internally for our own testing purposes. Both tools are command line utilities, and each has its own specific strengths.
• The fundamental goal with a high dynamic range, wide gamut pixel format is to never discard image information that falls outside the visible range. The entire tonal spectrum is always retained, regardless of the current exposure or color adjustments. Using fixed point or floating point values, pixel information is encoded using an extended numerical range. The visible portion of the numerical range is a subset of the total numerical range that can be encoded with fixed point or floating point values. . . . If color or exposure adjustment pushes a pixel value outside the visible range, rather than losing this value (as is the case with unsigned integer representations), the numerical value is still retained. If a subsequent adjustment brings that pixel value back into the visible range, the correct numerical value is fully recovered. This dramatically eliminates the issues and concerns with "flattening" a file. Most color or exposure adjustments are completely reversible, eliminating the need to restart with the original RAW file or an intermediate layered editing file.