Multiple-image Network Graphics

This document defines the MNG (Multiple-image Network Graphics) format. It also defines the MNG-LC (Low Complexity), MNG-VLC (Very Low Complexity), and JNG (JPEG Network Graphics) formats. These are proper subsets of MNG. MNG is a multiple-image member of the PNG (Portable Network Graphics) format family. It can contain animations, slide shows, or complex still frames, comprised of multiple PNG or JNG single-image datastreams. The MNG and JNG formats use the same chunk structure that is defined in the PNG specification, and they share other features of the PNG format. Any MNG decoder must be able to decode PNG and JNG datastreams. The MNG format (but not MNG-LC or MNG-VLC) provides a mechanism for reusing image data without having to retransmit it. Multiple images can be composed into a "frame" and a group of images can be used as an animated "sprite" that moves from one location to another in subsequent frames. "Palette animations" are also possible. MNG can also store images in a highly compressible "Delta-PNG" format, defined herein. This document includes examples that demonstrate various capabilities of MNG. These include simple movies, composite frames, loops, fades, tiling, scrolling, storage of voxel data, and converting GIF animations to MNG format. 4. MNG Chunks 4.1. Critical MNG control chunks 4.1.1. MHDR MNG datastream header 5. The JPEG Network Graphics (JNG) Format 5.1. Critical JNG chunks 5.1.1. JHDR JNG header 6. The Delta-PNG Format 6.1. Delta-PNG critical chunks 6.1.1. DHDR Delta-PNG datastream header 6.2. Ancillary Delta-PNG chunks 6.2.1. gAMA, cHRM, iCCP, sRGB Color space chunks This specification defines the format of a MNG (Multiple-image Network Graphics) format. It also defines low-complexity and very-low-complexity versions (MNG-LC and MNG-VLC), and the JNG (JPEG Network Graphics) format, which are proper subsets of MNG. Note: This specification depends on the PNG (Portable Network Graphics) [[PNG]]( and the JPEG (Joint Photographic Experts Group) specifications. The PNG specification is available at the PNG web site, Like PNG, a MNG datastream consists of an 8-byte signature, followed by a series of chunks. It begins with the MHDR chunk and ends with the MEND chunk. Each chunk consists of a 4-byte data length field, a 4-byte chunk type code (e.g., "MHDR"), data (unless the length is zero), and a CRC (cyclical redundancy check value). The embedded images can be PNG, JNG, or Delta-PNG datastreams. MNG-LC and MNG-VLC datastreams do not contain JNG datastreams, but MNG-LC and MNG-VLC applications can be enhanced to recognize and process JNG datastreams as well. The 8-byte MNG signature. The MHDR chunk. Frame definitions. A frame is one or more layers, the last of which has a nonzero interframe delay, composited against whatever was already on the display. Layer definitions. An embedded potentially visible image, described by PNG or JNG datastreams or the MNG BASI chunk (a foreground layer). An image that is generated from a stored object as directed by certain MNG chunks (a foreground layer). The background (a background layer). LOOP-ENDL chunks. SEEK chunks that mark points in the datastream where processing can be restarted. Various chunks for creating and manipulating images and other objects. The MEND chunk. MNG does not yet accommodate sound or complex sequencing information, but these capabilities might be added at a later date, in a backward-compatible manner. These issues are being discussed in the [email protected] mailing list. Chunk structure (length, name, data, CRC) and the chunk-naming system are identical to those defined in the PNG specification. As in PNG, all integers that require more than one byte must be in network byte order. The chunk copying rules for MNG employ the same mechanism as PNG, but with rules that are explained more fully (see below, Chapter 8 ). A MNG editor is not permitted to move unknown chunks across the SAVE and SEEK chunks, across any chunks