Editing StuffIt (section)

===StuffIt Image Format (SIF)===
Early in 2005, a new [[JPEG]] compression system was released that regularly obtained compression in the order of 25%<ref name="act-jpeg">{{cite web|last1=Gilchrist|first1=Jeff|title=ACT JPEG Compression Test|url=http://www.compression.ca/act/act-jpeg.html|website=www.compression.ca|language=en}}</ref> (meaning a compressed file size 75% of the original file size) without any further loss of image quality and with the ability to rebuild the original file, not just the original image. ([[ZIP (file format)|ZIP]]-like programs typically achieve JPEG compression rates in the order of 1 to 3%. Programs that optimize JPEGs without regard for the original file, only the original image, obtain compression rates from 3 to 10% (depending on the efficiency of the original JPEG). Programs that use the rarely implemented [[arithmetic coding]] option available to the JPEG standard typically achieve rates around 12%.)

The new technique was implemented as a StuffIt X format option in their ''StuffIt Deluxe'' product. They have also proposed a new image format known as SIF, which simply consists of a single JPEG file compressed using this new technique.

Pending filing of their patent, they retain knowledge of the details of this algorithm as a trade secret. Some details are disclosed in:<ref>{{cite book |last1=Salomon |first1=David |title=Handbook of Data Compression |date=18 January 2010 |isbn=9781848829039 |pages=1194|publisher=Springer }}</ref> the high JPEG recompression is achieved by undoing the last step of the JPEG compression itself (the Huffman encoding of quantized transform coefficients). Instead, the transform coefficients are compressed by a more efficient algorithm (a predictive model based on the DC coefficients of neighboring blocks). Similar techniques are also applied for other image file formats such as GIF and TIFF and even the MP3 music file format. By means of decomposition, the relatively high compression rates for individual file formats can also be achieved for container file formats such as PDF, PSD and even ZIP.