What is the fine-grained topic of the following text: On the other hand, our new image compression algorithm, HPA (Hierarchical Pixel Averaging); despite of being just a prototype, this lossless and fixed-quality lossy compressor offers ratio-versus-quality results comparable to those of the current space standard (CCSDS 122.0), and also comparable to those obtained with the JPEG standard. Only return the topic.
HPA (Hierarchical Pixel Averaging) Image Compression Algorithm