For the next century multimedia image application, we should be able to provide higher compression efficiency and more functions of image compression technology. In order to practice this dream, the new generation of static image compression standards, JPEG 2000, has begun to set up. This article mainly introduces the development status, principle and application of JPEG 2000.
JPEG (pronounced: Jay PEG), the full name is Joint Photographic Experts Group, a committee that is working on static image compression standards under the International Standards Organization (ISO). It worked out the first set of international static image compression standards, ISO 10918-1, commonly known as JPEG. Because of the excellent image quality of JPEG, it attracts the public's attention and has achieved great success in a short span of several years, and 80% of the images on the website are using JPEG compression standard.
However, with the increase of multimedia usage population and application domain, traditional JPEG compression technology can not satisfy the demand of multimedia image data. For the next century multimedia imaging applications, we need to be able to provide higher compression efficiency and more recent features of the new generation of image compression technology. In order to practice this dream, the new generation of static image compression standards, JPEG 2000, began to set up.
JPEG2000 Development Status
JPEG 2000, the official name of "ISO 15444", is also the responsibility of the JPEG organization. Since its inception in March 1997 and the beginning of public consultation with universities, companies and research institutions around the world, 22 proposals from major research groups have been submitted shortly. In November of that year, the 22 proposals were compared and tested, and the best technology was chosen to start building the so-called validation model (verification). Through continuous technical testing, the verification model gradually converge to a stable technology, the prototype of JPEG 2000 is generally completed. June 1999, JPEG 2000 into the next stage, that is, the so-called work report (working draft) of the writing, November 1999, JPEG 2000 Committee report (Committee draft) has been completed, the software and hardware manufacturers at this point in succession to jump into the production JPEG 2000 Series/decoder ranks together to divide the market large. It is expected that by November 2000, JPEG 2000 will be completed!
The principle of JPEG2000
The biggest difference between JPEG 2000 and traditional JPEG is that it discards the block coding method based on discrete-string transformation (discrete cosine Transform), and transforms the multiple-resolution coding method based on wavelet transform (Wavelet Transform). The main purpose of the wavelet transform is to extract the frequency component of the image. The following figure shows the results obtained by San Jiexiao conversion. The upper-left corner is the low-frequency part of the image, while the rest is the high-frequency portion of the image at different scales, in different directions (horizontal, vertical and diagonal). Usually, the low-frequency part retains the image's full picture, while the high-frequency part takes place at the so-called edge, the junction of two lines.
In the encoding of DCT (discrete-string conversion), imagine a image as a brick wall built by the DCT coefficients, and the bricks are composed of each DCT block. The act of compressing the image can be seen as opening the brick from the tail and tapping to reveal the gap, and squeeze the wall across the gap. On the brick wall after the squeeze, the cracked remains filled. This unsightly patch often occurs in the lower-level DCT compression method, as shown in the following figure.
However, in the wavelet transform, the created irregular gap occurs at the border of the two lines. In the brick wall after the squeeze, because it is better in the edge anastomosis, so that the cracks produced by the squeeze is not easy to detect, it will produce a smoother visual effect, the following figure.
At the same time, the wavelet transform technology makes JPEG 2000 more resilient, the characteristics include the user can see the complete picture when they receive a part of the file, the user may select the partial decompression of the frame selection flexibly, and the user can select the original color photo to extract into black and white or color, and when the lossless compression is adopted, You can choose to extract the distortion or distortion. However, regardless of how the image is presented, all the relevant information is contained in a single JPEG 2000 file.
JPEG 2000 is essentially an open standard, and is bound to replace the traditional JPEG format because of its distinctive features and features and the requirement that older versions be supported.
The application of JPEG2000
The development of JPEG 2000 is the application-oriented approach, that is, the application of the first to develop specifications. The application domain of JPEG 2000 can be roughly divided into two parts, one for the traditional JPEG market, such as printer, scanner, digital camera and so on, one for the new application domain, such as network transmission, wireless communication, medical imaging, etc. The companies that have been put in place have agreed that future JPEG 2000 licenses will be available free of charge.
JPEG Official website: http://www.jpeg.org/