F.1 ENCAPSULATED JPEG ENCODED IMAGES

The International Standards Organization (ISO/IEC JTC1/SC2/WG10) has prepared an International Standard, ISO/IS-10918-1 (JPEG Part 1) and International Draft Standard ISO/IS-10918-2 (JPEG Part 2), for the digital compression and coding of continuous-tone still images. This standard is collectively known as the JPEG Standard.

Part 1 of the JPEG Standard sets out requirements and implementation guidelines for the coded representation of compressed image data to be interchanged between applications. The processes and representations are intended to be generic in order to support the broad range of applications for color and grayscale still images for the purpose of communications and storage within computer systems. Part 2 of the JPEG Standard defines tests for determining whether implementations comply with the requirements of the various encoding and decoding processes specified in Part 1 of the JPEG Standard.

The JPEG Standard specifies lossy and lossless code processes. The lossy coding is based on the discrete cosine transform (DCT), permitting data compression with an adjustable compression ratio. The lossless coding employs differential pulse code modulation (DPCM).

The JPEG Standard permits a variety of coding processes for the coder and decoder. These processes differ in coding schemes for the quantified data and in sample precision. The coding processes are consecutively numbered as defined in the International Draft Standard ISO/IS-10918-2 (JPEG Part 2), and are summarized in Table F.1-1. The simplest DCT-based coding process is referred to as Baseline Sequential with Huffman Coding for 8-bit Samples.

Table F.1-1 JPEG Modes of Image Coding

No. Description Lossy LY / Lossless LL Non-Hierarchical NH / Hierarchical H Sequential S / Progressive P Transform Coding Accepted Bits
1 Baseline LY NH S DCT Huffman 8
2 Extended LY NH S DCT Huffman 8
4 Extended LY NH S DCT Huffman 12
14 Lossless LL NH S DPCM Huffman 2-16

The different coding processes specified in the JPEG Standard are closely related. By extending the capability of an implementation, increasingly more 'lower level' processes can also be executed by the implementation. This is shown in Table F.1-2 for Huffman Coding.

Inclusion of a JPEG-coded image in a DICOM message is facilitated by the use of specific Transfer Syntaxes that are defined in Annex A. Independent of the JPEG coding processes, the same syntax applies. The only distinction for different processes in the syntax is the UID value. Table F.1-5 lists the UID values in the Transfer Syntax for the various JPEG coding processes for reference.

Table F.1-2 RELATIONSHIP BETWEEN THE LOSSY JPEG HUFFMAN CODING PROCESSES

* Coding process of column can execute coding process of row

Process 1 2 4
1 * * *
2 * *
4 *

Table F.1-5 Identification of JPEG Coding Processes in DICOM

Process 1 2 4
1.2.840.10008.1.2.4.50 1 baseline 1
1.2.840.10008.1.2.4.51 2,4 extended 1,2,4
1.2.840.10008.1.2.4.57 14 lossless NH 14
1.2.840.10008.1.2.4.70 14 Selection Value 1 lossless NH, first-order prediction