Views are expressed on desirable characteristics of image data compression schemes for PACS, in particular, that such schemes should not only enable reversible and irreversible compression but also provide user-friendly features and compatibility with PACS requirements. Among the image conversion schemes for data compression, hierarchical picture decomposition meets most of the desirable features and requirements, such as ease of composing a pictorial index of a patient file, adaptation of transmission to the variable resolution requirements in PACS, quasi-instant transmission of low-resolution pictures for teleradiology, and ease of implementing spatial pyramid filters. One of the simplest image conversion schemes which fulfills these requirements is the S-transform. Among the coding methods, the Lempel-Ziv scheme offers features which could be advantageous for PACS applications, such as that the code is always optimal - even though it is derived from a single-pass operation, that it may have fixed length, and that the code table does not need to be transmitted. Results of reversible and irreversible data compression with the S-transform, Lempel-Ziv coding, and quantizer functions are presented for computed radiographs and magnetic resonance images. The results are assessed and compared with S-transform/Huffman coding as well as differential pulse code modulation with Huffman or Lempel-Ziv coding.