Everything about Jpeg 2000 totally explained
JPEG 2000 is a
wavelet-based
image compression standard. It was created by the
Joint Photographic Experts Group committee in the year 2000 with the intention of superseding their original
discrete cosine transform-based
JPEG standard (created about 1991). The standardized
filename extension is
.jp2 for
ISO/
IEC 15444-1 conforming files and
.jpx for the extended part-2 specifications, published as ISO/IEC 15444-2, while the
MIME type is
image/jp2.
JPEG 2000 requires far greater decompression time than JPEG and allows more sophisticated progressive downloads, yet averages similar compression rates. JPEG 2000 becomes increasingly blurred with higher compression ratios rather than generating JPEG's "blocking and ringing"
artifacts, complicating direct comparison of their respective compression rates.
Part of JPEG 2000 has been published as an
ISO standard, ISO/IEC 15444-1:2000.
As of 2008, JPEG 2000 isn't widely supported in
web browsers, and hence isn't generally used on the
World Wide Web.
Even though provisions have been made to integrate all kinds of external meta-data, there's currently no accepted way to embed
Exif data (although a JPEG 2000 "
JpgTiffExif->JP2" UUID box to store EXIF information has been proposed, and is implemented by
ExifTool
version 6.92 or later).
Features
- Superior compression performance: At high bit rates, where artifacts become nearly imperceptible, JPEG 2000 has a small machine-measured fidelity advantage over JPEG. At lower bit rates (for example, less than 0.25 bits/pixel for gray-scale images), JPEG 2000 has a much more significant advantage over certain modes of JPEG: artifacts are less visible and there's almost no blocking. The compression gains over JPEG are attributed to the use of DWT and a more sophisticated entropy encoding scheme.
Multiple resolution representation: JPEG2000 decomposes the image into a multiple resolution representation in the course of its compression process. This representation can be put to use for other image presentation purposes beyond compression as such.
Progressive transmission by pixel and resolution accuracy, commonly referred to as progressive decoding and signal-to-noise ratio (SNR) scalability: JPEG2000 provides efficient codestream organizations which are progressive by pixel accuracy and by image resolution (or by image size). This way, after a smaller part of the whole file has been received, the viewer can see a lower quality version of the final picture. The quality then improves progressively through downloading more data bits from the source. The 1991 JPEG standard also has a progressive transmission feature but it's rarely used.
Lossless and lossy compression: Like JPEG 1991, the JPEG2000 standard provides both lossless and lossy compression in a single compression architecture. Lossless compression is provided by the use of a reversible integer wavelet transform in JPEG 2000.
Random codestream access and processing, also referred as Region Of Interest (ROI): JPEG2000 codestreams offer several mechanisms to support spatial random access or region of interest access at varying degrees of granularity. This way it's possible to store different parts of the same picture using different quality.
Error resilience: Like JPEG 1991, JPEG2000 is robust to bit errors introduced by noisy communication channels, due to the coding of data in relatively small independent blocks.
Flexible file format: The JP2 and JPX file formats allow for handling of color-space information, metadata, and for interactivity in networked applications as developed in the JPEG Part 9 JPIP protocol.
Side channel spatial information: it fully supports transparency and alpha planes.
More advantages associated with JPEG 2000 can be referred to from the Official JPEG 2000 page.
Technical discussion
The aim of JPEG 2000 isn't only improved compression performance over JPEG but also adding (or improving) features such as scalability and editability. In fact, JPEG 2000's improvement in compression performance relative to the original JPEG standard is actually rather modest and shouldn't ordinarily be the primary consideration for evaluating the design. Very low and very high compression rates are supported in JPEG 2000. In fact, the graceful ability of the design to handle a very large range of effective bit rates is one of the strengths of JPEG 2000. For example, to reduce the number of bits for a picture below a certain amount, the advisable thing to do with the first JPEG standard is to reduce the resolution of the input image before encoding it. That's unnecessary when using JPEG 2000, because JPEG 2000 already does this automatically through its multiresolution decomposition structure. The following sections describe the algorithm of JPEG 2000.
Color components transformation
Initially, images have to be transformed from the RGB color space to another color space, leading to three components that are handled separately. There are two possible choices:
Irreversible Color Transform (ICT) uses the well known YCBCR color space. It is called "irreversible" because of the quantization errors it introduces.
Reversible Color Transform (RCT) uses a modified YUV color space that doesn't introduce quantization errors, so it's fully reversible. The transformation matrices are: » 
