JPEG 2000
A raster image compression standard and coding system.
JPEG 2000, officially recognized as the ISO 15444-1 standard, is a significant part of the digital and satellite mapping industry. It is created as an image coding system to enhance the JPEG format's shortcomings. It encompasses not only the standardization of a file format but also a code stream that provides superior image compression performances.
JPEG 2000 supports both lossless (exact) and lossy (approximate) compression within a single Codestream, permitting the decoding of the same Codestream at different resolutions and quality levels. An interesting aspect of JPEG 2000 is its scalability: once an image is encoded, it can be efficiently decoded to yield a version of the image at a smaller resolution or lower quality.
JPEG 2000 utilizes a Discrete Wavelet Transform (DWT) to transform the image from the spatial to the frequency domain. DWT separates images into sub-bands which are categorized into different resolutions and different types. This division allows the image to be compressed more efficiently.
This file format and code system supports various color spaces (like sRGB, YCbCr, XYZ, and Lab), binary transparency and alpha transparency, natural rendering of grey-scale images, and, of course, high dynamic range (HDR) imagery. Additionally, JPEG 2000 supports a wider range of bit depths (up to 16 bits per channel), versus the 8 bits per channel of original JPEG.
JPEG 2000 immensely contributes to the GIS field. Particularly in cases where the land is constantly changing—agriculture, forestry, and urban environments—high-quality imagery available in smaller file sizes enables more efficient system performance.
The metadata flexibility is one of the key benefits JPEG 2000 brings to GIS. Multiple types of metadata (geospatial location, image descriptions, legal information, etc.) can be embedded with the image. The format supports XML metadata, making it easier to standardize across different systems and processes and promotes interoperability.
JPEG 2000 has been implemented in several GIS and Remote Sensing software packages, providing reduced storage and enhanced sharing of geospatial data. However, its computational complexity is perceived as a hindrance, whereby the encoding and decoding process can be slower in some instances compared to other formats.
Despite this, JPEG 2000 is evolving, with advancements in hardware and software, delivering better efficiency, which credits its position as a favoured format in GIS. Enhancing application performances, such as digital cinema, printing, streaming, archiving, and various GIS-specific tasks, JPEG 2000's improved precision and adjustable compression ratios continue to provide remarkable possibilities in the realm of geospatial data.
