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 and Opportunity both used ICER. Onboard image compression is used extensively to make best use of the downlink resources. The Curiosity rover supports the use of ICER for its navigation cameras (but all other cameras use other file formats).

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.