ICER

:"This article is about the spacecraft image file format: in economics, ICER may refer to the incremental cost-effectiveness ratio."

ICER is a wavelet-based image compression file format used by the NASA Mars Rovers. ICER has both lossy and lossless compression modes.

The Mars Exploration Rovers “Spirit” (MER-A) and “Opportunity” (MER-B) both use ICER. Onboard image compression is used extensively to make best use of the downlink resources.

Most of the MER images are compressed with the ICER image compression software. The remaining MER images that are compressed make use of modified Low Complexity Lossless Compression (LOCO) software, a lossless submode of ICER.

ICER is a wavelet-based image compressor that allows for a graceful trade-off between the amount of compression (expressed in terms of compressed data volume in bits/pixel) and the resulting degradation in image quality (distortion). ICER has some similarities to JPEG2000, with respect to select wavelet operations.

The development of ICER was driven by the desire to achieve high compression performance while meeting the specialized needs of deep space applications.

Design commonalities with the JPEG2000 compressor

JPEG 2000 has some design commonalities with the ICER image compression format that is used to send images back from the Mars rovers.

ICER (like JPEG 2000) is wavelet-based and provides
* progressive compression.
* lossless compression (using the LOCO compressor).
* lossy compression.
* image context error correction to limit the effects of data loss on the deep-space channel.

ICER overall provides lossy compression performancecompetitive with the JPEG2000 image compression standard.

ICER-JPEG 2000 Common Features
* Both offer a variable number of image tiles to increase compression effectiveness over the deep space channel. Image tiles reduce demands on memory and processing time.
* Both offer a 'byte' quota.
* Both offer a 'quality' quota.

ICER-JPEG 2000 Differences

* JPEG 2000 uses floating point math, ICER uses only integer math.
* ICER reverts to a separate internal LOCO (Low Complexity Lossless Compression) compressor for lossless image compression.
* JPEG 2000 implements a different lossless compressor concept by running its wavelet compressor in a lossless mode.
* ICER and JPEG 2000 encode color spaces differently.
* ICER in its current form does compress monochrome images better than colour images due to its origins as an internal NASA Deep Space Network file format.
* ICER is subject to less than 1% overshoot when byte and quality quotas are in effect. On the other hand JPEG2000 codecs are typically designed never to overshoot their byte quotas.

When should one use ICER

ICER was created for low end 32 bit CPUs (essentially embedded computers) on spacecraft. It was finally used for the Mars Exploration Rovers. It has never been used for any real time application, only near real time.

JPEG2000 has been used by many image processing applications in near real time. However there are intellectual property issues with JPEG2000 relating to using JPEG2000 libraries and with one of the wavelet transforms. These intellectual issues must be considered when choosing a wavelet compression format.

Hewlett-Packard's Remote Graphics Software uses a video codec called HP3 (codec) which claims to derive from Mars Rover compression - this could be a real-time implementation of ICER. [ [http://www.augi.com/publications/hotnews.asp?page=1751 Autodesk User Group International: "April 2008"] "HP Remote Graphics Software (RGS) ... [uses] ... an HP patented compression algorithm developed for the NASA Mars Rover program that compresses and encrypts graphics data"]

External links

* [http://www.google.com/url?sa=t&ct=res&cd=2&url=http%3A%2F%2Fipnpr.jpl.nasa.gov%2Fprogress_report%2F42-155%2F155J.pdf&ei=6caKSL2tLaSAigG22cTjDA&usg=AFQjCNFaCYZCZQPI8HDmlRXysAei0n_eMQ&sig2=L6Q0uBAnkQ0HuaMgqrXYpQ The ICER Progressive Wavelet Image Compressor (PDF)]