The JPEG 2000 standard was designed to support the efficient electronic dissemination of digital documents and images to multiple end users. A properly designed system can leverage the encoding and decoding options of JPEG 2000 to provide end users with Just Enough Quality delivered Just in Time.
JPEG 2000 allows reduced resolution images to be quickly and efficiently extracted from a compressed file. This capability is useful for generating index or catalog pages with thumbnails of each image. With JPEG 2000, sub resolution images of various size can be extracted from the single compressed file and do not need to be stored separately.
JPEG 2000 also allows reduced quality images to be extracted from a compressed file, producing images with higher effective compression ratios optimized for specific workflows.
Lossless Compression and Lossy Decompression
This implementation of quality scalability elegantly supports remote viewing and access of large losslessly compressed image files. For archival and reference purposes, a lossless image at 2:1 compression can be stored on the server. From this master file, a medium quality image at 30:1 compression can be extracted and transmitted for browsing, and a high quality image at 10:1 compression can be extracted and viewed for most research. JPEG 2000 allows the more highly compressed images to be quickly extracted from the single master file. With the layered file format, only the additional layers must be transmitted to progress to a higher quality image.
JPEG 2000’s progressive transmission format displays a low resolution version of an image after only a small portion of the file has been received. As more data arrives, the display is progressively refined until the full resolution image is shown. This feature allows a user to quickly orient themselves to an image, reducing the time spent waiting for data to arrive.
User interface for the Aware large image encoder/decoder tool (source code included) – This shows Resolution 2 of 5 for each tile. Those tiles bounded by red overlay have yet to be fully decoded.
Rich Support for Metadata
The comprehensive and flexible nature of metadata support within JPEG 2000 makes it ideal for digital archives.
Part 1 baseline JPEG 2000 supports embedded metadata in the following ways:
- Inclusion of comments directly in the codestream: The comments can be either ISO Latin 15 text or binary in format. The length of each text string can be up to 64 kbytes and the text strings can be placed in the main file header or the header for each tile if the image is tiled
- JP2 File Format: JP2 is an optional file format that may be used to wrap JPEG 2000 codestreams. The file format includes capabilities to specify the colorspace of the image, alpha channel information, and large amounts of metadata. Multiple JPEG 2000 codestreams can be wrapped into a single JP2 file. All information in a JP2 file is included in entities called “boxes”. For example, a specific box type is used to include a JPEG 2000 codestream, a different one is used to include colorspace information.
The JP2 file format defines the following box types for the inclusion of metadata into the JP2 file:
- Intellectual Property Box – Used for carrying intellectual property rights information about the image(s) in the file.
- XML Box – Used for vendor specific information in XML format.
- URL Box – Used for including an URL that can be used by an application to acquire more information about the associated image or vendor.
- UUID Box – Used for any other information not covered by above metadata boxes.
The UUID box is the most versatile metadata mechanism. It allows the user or application to associate any type of information with the image file in a specific place. Decoders that are designed to read JP2 files with this information included can extract it easily, while others can disregard it completely.