The still image compression format now known as JPEG XR has its roots at Microsoft Research. It started as the Progressive Transform Codec (PTC), which we designed back in 1999 as an alternative to JPEG 2000. The goal for PTC was to achieve a compression performance similar to that of JPEG 2000, but with a much lower (by ~ 3x) computational complexity, less than 2x that of the original low-complexity JPEG format. PTC was also designed with two new features that distinguished it from JPEG and JPEG 2000:
- Using lapped biorthogonal transforms. Such transforms do not produce visible blocking artifacts like those from JPEG at high compression ratios. They have lower computational complexity and lower memory footprint than the wavelet transforms used in JPEG 2000. They also have a higher “coding gain” (which defines limits on compression performance) than the discrete cosine transform (DCT) used in JPEG.
- New YCoCg color transform, which has higher compression efficiency and lower computational complexity than the commonly-used YCrCB (YUV).
- All-integer arithmetic. All internal computations are in integer arithmetic, even for compression of images where pixels values are stored in floating-point format. That enables several advantages, such as lossy and lossless compression within the same algorithm, and ease of test of standard decoders, as they should produce bit-exact output when correctly implemented.
- Many other features, such as support of 32-bit pixels, many color channels (e.g. RGB plus alpha), low-resolution thumbnails automatically embedded in the bitstream, and support for region-of-interest decoding with reduced decoding time.
PTC was used in several applications, including encoding of game textures for XBox game discs. In a close collaboration between the Microsoft Research and Microsoft Windows groups, the PTC codec evolved into the HD Photo (a.k.a. Windows Media Photo) codec. The HD Photo codec was then submitted to standards committees, and was approved by both the ISO and the ITU-T as the JPEG XR format.
The JPEG XR format is now widely used in Microsoft products and services, in particular in Microsoft Office, where often pictures in PowerPoint or Word files are internally stored in HD Photo / JPEG XR format.
A well-tested JPEG XR plugin for Adobe Photoshop can be found here.