Integration of relevant metadata in images provides an opportunity for participating industries to take image processing to the next level. Image metadata is essentially nonpicture information that is bundled with picture information in a file. Metadata can include information such as the date and time the picture was taken, whether a flash was used, which camera model was used and even audio annotations.
Metadata is a key supporting technology for content management. The content management services built into the Microsoft Windows Millennium Edition (Windows Me) and later Windows operating systems uses metadata extensively.
Metadata helps users organize digital images. As digital cameras and scanners become more widely available, users are faced with managing hundreds or thousands of images.
Using the content-management capabilities of the Windows operating systems, users can sort and search their images on metadata items such as date and time, camera make and model, or location.
For example, users might add titles and GPS location data to images in a real-estate workflow. Or, insurance adjusters might sort images by the time they were taken, to correspond to blocks of appointments.
Users might add voice annotations to some images, and later sort images with voice annotations, to listen to them or transcribe them all together, rather than searching each image individually.
In addition, metadata helps devices render digital images with higher quality. Currently, devices render images as best they can, based on average settings for the average image. Improving the quality of a given rendering requires the user to make manual adjustments.
Vendors can use metadata such as brightness and exposure bias to refine device algorithms for rendering images to produce higher-quality images automatically, with less need for user intervention. They can also enhance image reproduction. For example, suppose a vendor produces both digital cameras and printers. Having metadata available to the printer driver allows the vendor to enhance the end-to-end quality of the image reproduction system.
Microsoft is supporting metadata in image files through GDI+, the next-generation graphics engine for 2-D vector graphics, imaging and typography for Windows-based and Web-based applications. GDI+ (graphics device interface) supports a number of native still-image file formats, including BMP, EXIF, JPEG, TIFF, PNG and GIF. In turn, GDI+ provides core services for managing files in these formats to Microsoft Windows platforms.
Vendors can use GDI+ to read and modify metadata in image files. GDI+ makes more extensive use of metadata in image files than earlier versions of Windows operating systems, and more image metadata is exposed to users. Vendors who generate image files are encouraged to store valid and presentable information in all possible metadata items.
Application developers are also encouraged to use Windows image acquisition (WIA) to set device properties that generate metadata if the camera supports that behavior. For example, an application might recognize that the date and time of an image are missing and communicate with the device through WIA to set those values so that subsequent images will contain date and time metadata.
A common baseline set of metadata promotes widespread use of specific metadata by the industry and consumers. It also makes it possible to provide developers with simple and consistent interfaces for accessing metadata in their applications.
A baseline set of metadata should follow certain guidelines. It should be consistent with current de facto industry standards, such as Jeida's EXIF set of metadata. It should also include a standard minimal set of metadata intended for use by end users. It should be easily transferable across file formats.
For example, it should be possible to capture an image with a digital camera in an EXIF file and convert it to a PNG file for posting on a Web site while preserving all of the metadata from the EXIF file.
Image files should include a metadata item that can contain a list of search keywords, separated by a comma or semicolon. A search-keyword metadata item adds value to image files. For example, the operating system can search keyword information transparently to sort and manage image files within the system.
Image metadata in GDI+ is indirectly related to any standard file format, because GDI+ provides an interface between different standard file formats and their metadata. As part of its core graphics technology, GDI+ supports metadata in the following ways:
- It abstracts the metadata interface, so applications can write to a simple and consistent interface for accessing metadata independently of the file format.
- It provides the infrastructure necessary to support content management, a strategic feature for Windows-based imaging applications, so developers are not required to implement content management separately in their applications.
Content management plus a consistent set of metadata makes it possible for users to organize and search stored images by metadata values, such as the time a picture was taken or its location. GDI+ supports a number of image file formats-TIFF, EXIF, JFIF, GIF, PNG and BMP-and can map standard metadata items between them.
When converting a file from one format to another, GDI+ preserves all possible metadata items in the destination file format. GDI+ also preserves metadata across image-altering operations whenever possible. For example, developers can take advantage of a GDI+ function to perform lossless 90-degree rotations in JPEG. GDI+ updates standard metadata items, such as thumbnail, width, height and orientation, to reflect the rotated image.