Image coding design considerations for cascaded encoding-decoding cycles and image editing: analysis of JPEG 1, JPEG 2000, and JPEG XR / HD Photo

摘要

This paper discusses cascaded multiple encoding/decoding cycles and their effect on image quality for lossy image coding designs. Cascaded multiple encoding/decoding is an important operating scenario in professional editing industries. In such scenarios, it is common for a single image to be edited by several people while the image is compressed between editors for transit and archival. In these cases, it is important that decoding followed by re-encoding introduce minimal (or no) distortion across generations. A significant number of potential sources of distortion introduction exist in a cascade of decoding and re-encoding, especially if such processes as conversion between RGB and YUV color representations, 4:2:0 resampling, etc., are considered (and operations like spatial shifting, resizing, and changes of the quantization process or coding format). This paper highlights various aspects of distortion introduced by decoding and re-encoding, and remarks on the impact of these issues in the context of three still-image coding designs: JPEG, JPEG 2000, and JPEG XR. JPEG XR is a draft standard under development in the JPEG committee based on Microsoft technology known as HD Photo. The paper focuses particularly on the JPEG XR technology, and suggests that the design of the draft JPEG XR standard has several quite good characteristics in regard to re-encoding robustness.