What is a JXR file?

JPEG XR (JPEG extended range) is a file format for continuous tone photographic images. It is a still-image compression standard that is based on HD Photo developed by Microsoft. It supports both lossy and lossless compression.

Brief History

Windows Media Photo was first announced by Microsoft at WinHEC 2006. It was renamed HD Photo in November 2006. JPEG XR was approved as International Standard ISO/IEC 29199-2 on 19 June 2009. The ITU-T and ISO/IEC published a motion format specification (ITU-T T.833 | ISO/IEC 29199-3), a conformance test set (ITU-T T.834 | ISO/IEC 29199-4), and reference software (ITU-T T.835 | ISO/IEC 29199-5) for JPEG XR after the completion of the image coding specification in 2010. A technical report describing the workflow architecture for JPEG XR was published in 2011.

JPEG XR Design

As compared to JPEG, JPEG XR offers several improvements including:

  • Better Compression: JPEG XR offers higher compression ratios.
  • Lossless Compression: JPEG XR supports lossless compression.
  • Tile Structure: JPEG XR image can be segmented into tile regions where each region can be decoded separately.
  • More color accuracy: JPEG XR includes internal conversion to the YCoCg color space for supporting images using RGB color space. JPEG XR also supports a 16-bit per component (64-bit per pixel) integer CMYK color model. JPEG XR supports RGBE shared-exponent floating point color format for HDR images. JPEG XR supports grayscale and multi-channel color encodings as well.
  • Transparency Map: JPEG XR supports the alpha channel for transparency.
  • Compressed-domain image modification: JPEG XR images can be converted to lossy encoding, reduced in resolution, cropped, flipped, rotated, and the tile structure can be altered all without full decoding of the file.
  • Metadata Support: JPEG XR image file may contain ICC color profile for consistent color representation across multiple devices. The format also supports Exif and XMP metadata formats.

Container Format

JPEG XR image data can be stored in TIFF-like container format by using a table of Image File Directory (IFT) tags. A JXR file contains the following in IFD tags:

  • Image data: It is a contiguous self-contained image data.
  • Optional alpha channel data: If this is present, the image data can be compressed separately enabling the support of applications that do not support transparency.
  • Metadata
  • Optional XMP metadata
  • Optional Exif metadata

As it is based on TIFF format, it inherits all of the TIFF format limitations like the 4 GB file size limit.

References

See Also