The conventional wisdom was that already-compressed files cannot be compressed again.
However, a new exquisite image compression technology that had been viewed as unobtainable by many has been successfully developed by a Korean image processing guru for the first time in the world. Hyoung Joong Kim, professor at Graduate School of Information Security, Korea University has succeeded in compressing image files in the JPEG format (a standard method of lossy plus lossless compression for digital photography).
Generally speaking, the probability of every symbol is put to use at the final stage of bit-rate reduction or data compression. Since compression algorithms have fully exploited the probability of every symbol, making attempts to compress them again by reusing the probability of each symbol is impossible. Therefore, Professor Kim has come up with a trailblazing data compression method: hiding information in compressed files using a reversible data hiding technique. His compression algorithm embeds message into the compressed bit stream, and hidden information can be extracted and compared with the uncompressed image states.
Professor Kim’s data compression method enables the possibility of further compressing already-compressed still image files as well as video data (including MPEG and H.264 files). In other words, regardless of what kind of data compression algorithm was used, all types of image files can be further reduced in size. Once a compressed file is uncompressed, its original image is restored and referenced. Clues to hidden message can be discovered from the uncompressed image (See the pictures below). Hidden information is extracted in a reversible manner based on whether each piece of the restored content fits well with its surroundings, which is the basic principle of the decompression method.
With the advent of file compression standards such as JPEG and MPEG, the world has been ushered into the smart media era. However, the industry still covets faster, more efficient compression technologies that boast high compression rates. The more technology advances, the more vivid images users demand. As a result, the size of files is getting bigger and bigger at a breakneck pace that has even ultra-high speed networks panting. Accordingly, faster, more advanced file compression technologies are needed as the key to making the world a smarter place. Professor Kim’s unprecedented file compression mechanism seems to give a much-needed impetus to revolutionizing the smart device industry.
Unfortunately, not all of the compressed files can be compressed again. As it stands now, this new technology is applicable only to image files. Yet, its coverage is likely to extend to audio files and documents in the foreseeable future. The development of this data compression method is funded by National Research Foundation (NRF) of Korea, and 3DLife.
Reversible data hiding technique allows us to extract hidden message and have the original image uncompressed without error. It is the first time for such a technique to be utilized for image file compression as opposed to image authentication.
Hyoung Joong Kim, Professor at Korea University, graduated in electrical engineering from Seoul National University and received his PhD degree from the same university. He is renowned for his unrivalled expertise in reversible data hiding technology, steganography, and multimedia forensics.
