DocStructOPJv2 (original) (raw)

Introduction

Based on the work done by Jerome Fines in 2008, the OpenJPEG team has decided in June 2011 to merge the V2 branch in the trunk. The goal of this operation is to release an official version of this work which will become the reference for the future development. Here we will describe and discuss about the evolution of structures in OpenJPEG.

Main public structures

Structures found in openjpeg.h

opj_stream_t

Abstract JPEG2000 stream:

• created from file or external stream
• linked to opj_stream_private_t structure inside the lib

opj_codec_t

Abstract JPEG2000 codec (handle on the compressor or decompressor):

• created from the codec format selected
• linked to opj_codec_private_t structure inside the lib

opj_dparameters_t / opj_cparameters_t

Structure provide for the users to give respectively decompression and compression parameters to the lib.

opj_image

Structure where are stored image information and image component structure

opj_image_comp_t

Structure where are stored image component information and data

opj_codestream_info_v2_t

Structure which give to the user the main information about the codestream included in the JPEG2000 file/stream:

• Tile size and origin
• Number of tile
• Default information about tile compression -> opj_tile_info_v2_t structure
• For each tile the compression parameters (NOT USED for the moment) -> opj_tile_info_v2_t structure

opj_tile_info_v2_t

Structure which give visibility about the main tile compression parameters for one specific tile. The first part of this structure is common to all tile-component included in the tile:

• tile index
• coding style
• progression order
• number of layers
• MCT identifier
• Structure which store compression parameters for one tile component -> opj_tccp_info_t

opj_tccp_info_t

Structure which give visibility about low-level compression parameters for one tile component

opj_codestream_index_t

Structure which give to the user the main information about the position of main elements in the codestream included in the JPEG2000 file/stream:

• main header positions (start and end)
• codestream size
• structure which store the position of the main marker (SOC, SOT, SOD, EOC and main header markers) -> opj_marker_info_t
• structure which store the information about position of markers inside each tile independently -> opj_tile_index_t

opj_marker_info_t

Structure which store markers type and position and length in the codestream.

opj_tile_index_t

Structure which store the information about the index of elements in the tile:

• tile index
• structure which store the position of the markers in the tile header -> opj_marker_info_t
• structure which store information about tile part position of this tile -> opj_tp_index_t
• structure which store information about packet position of this tile -> opj_packet_info_t

opj_tp_index_t

Structure which store position of a tile-part and its header in the codestream

opj_packet_info_t

Structure which store information concerning a packet inside tile

Some private structures

We will described here the main structures used in openjpeg.c, cio.h, j2k.h and jp2.h

opj_stream_private_t

It is the main internal structure to manage the byte input/output on the stream. It give access to the user data (file or external stream) and the main functions to handle the stream (read, write, move in the stream). Its give access to the buffer.

opj_codec_private_t

It is the main codec handler used for compression or decompression. Its contains:

• an union which manage decompression and compression handlers -> opj_compression_t or opj_decompression_t
• the flag which indicate if the codec is a decompressor or compressor
• the event manager structure -> opj_event_mgr_t
• the internal codestream information structure -> opj_codestream_info_v2_t
• the internal codestream index structure -> opj_codestream_index_t
• the internal codec which depends the JPEG2000 codec used (J2K or JP2 or (JPT)) -> opj_j2k_v2_t / opj_jp2_v2_t

opj_compression_t

Move during the first part of merge but not used for the moment. It is the compression handlers generic to j2k or jp2 codec

opj_decompression_t

Structure which give access to all generic decompression handlers.

opj_event_mgr_t

Message handler object used to manage the messages (error, warning and info) to the lib user.

opj_j2k_v2_t

Internal J2K codestream reader/writer. It is the main place where we can find the elements used in the J2K compression/decompresion process. Here we will now describe the structures used in the decompression process :

• some parameters about decompression process -> opj_j2k_dec_t
• a private image structure which is used to store only the information about the whole output image (no data store in) -> opj_image_t
• an output image to store the decoded image or sub part.
• the coding parameters which describe how the codestream is encoded -> opj_cp_v2_t
• Two lists of procedure used to provide a more generic framework to the functions used in j2k codec
• the internal codestream index -> opj_codestream_index_t
• the internal structure which manage the tile coding/decoding operation -> opj_tcd_v2

opj_jp2_v2_t

Internal JP2 reader/writer structure. The JP2 codec must be considered as a set of boxes which enclose the J2K codestream. The goal of these boxes is to give clue to interpret the raw codestream. This structure follow this scheme and embedded a opj_j2k_v2_t structure. Moreover it is composed of:

• some parameters
• a structure to handle the color interpretation -> opj_jp2_color_t
• Two lists of procedure used to provide a more generic framework to the functions used in jp2 codec