Image compression for the silicon drift detectors in the ALICE experiment

We describe an algorithm for the zero suppression and data compression for the Silicon Drift Detectors (SDD) in the ALICE experiment. The algorithm operates on 10-bit linear data streams from the SDDs by apply ing a 10 bit to 8-bit non-linear compression followed by a data reduction b ased on a two-threshold discrimination and a two-dimensional analysis along both the drift time and the anodes. The proposed scheme allows for a bette r understanding of the neighborhoods of the SDD signal clusters, thus impro ving their reconstructability, and also provides a statistical monitoring o f the background characteristics for each SDD anode. The entire algorithm is purely combinatorial and thus can be executed in pi peline, without additional clock cycles, during the SDD readout. The hardwa re coding together with the methods for the expansion to the original 10-bi t values in the offline analysis and for the background monitoring are pres ented. (C) 2001 Elsevier Science B.V. All rights reserved.