We present the implementation of a volumetric JPEG 2000 codec as a real-world use case of software acceleration with GPUs and multi-core CPUs. We present a generic methodology to accelerate existing code written in C with OpenCL. Furthermore, we account for the volumetric nature of the processed data and formulate associated optimization guidelines. The resulting software can exploit different accelerator types - GPUs and multi-core CPUs - and delivers a decent speedup on a variety of hardware platforms for a relatively small effort.