A survey of on-board image compression for CNES space missions

Images acquired on board spacecraft represent in most cases very large volumes of data. It is then necessary to store these data and to transmit them to ground. It is essential to reduce to a minimum the on-board storage capacity and the on-board transmission rate. On board image compression is advantageous for two main reasons: 1) the steady performance improvements of compression algorithms, and 2) the availability in recent years, for spaceborne applications, of highly integrated custom circuits (ASIC technology) which makes it possible to implement, in high pixel rate systems, sophisticated real-time compression schemes. The authors focus on lossy compression algorithms used for CNES space missions. Such a typical image coder has three basic components: a transformation, a quantizer and data coding. In lossy compression the reconstructed image contains degradations relative to the original. As a result, much higher compression can be achieved as compared to lossless compression. More compression is obtained at the expense of more distortion. In order to be acceptable, these degradations (image quality) must be compatible with all the potential uses of the images. It is then very important to consider the whole image chain (from the sensor to the on-ground post-processing) to optimize image compression and for each space mission it is necessary to solve the trade-off between image quality versus compression ratio