t4.h

传真通信V27 V29 V17 T38解调与解码

/*
 * SpanDSP - a series of DSP components for telephony
 *
 * t4.h - definitions for T.4 fax processing
 *
 * Written by Steve Underwood <[e-mail]>
 *
 * Copyright (C) 2003 Steve Underwood
 *
 * All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2, as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 * $Id: t4.h,v 1.34 2007/08/02 13:55:48 steveu Exp $
 */

/*! \file */

#if !defined(_SPANDSP_T4_H_)
#define _SPANDSP_T4_H_

/*! \page t4_page T.4 image compression and decompression

\section t4_page_sec_1 What does it do?
The T.4 image compression and decompression routines implement the 1D and 2D
encoding methods defined in ITU specification T.4. They also implement the pure
2D encoding method defined in T.6. These are image compression algorithms used
for FAX transmission.

\section t4_page_sec_1 How does it work?
*/

enum
{
    T4_COMPRESSION_ITU_T4_1D = 1,
    T4_COMPRESSION_ITU_T4_2D = 2,
    T4_COMPRESSION_ITU_T6 = 3
};

enum
{
    T4_X_RESOLUTION_R4 = 4019,
    T4_X_RESOLUTION_R8 = 8037,
    T4_X_RESOLUTION_R16 = 16074
};

enum
{
    T4_Y_RESOLUTION_STANDARD = 3850,
    T4_Y_RESOLUTION_FINE = 7700,
    T4_Y_RESOLUTION_SUPERFINE = 15400
};

/*!
    T.4 FAX compression/decompression descriptor. This defines the working state
    for a single instance of a T.4 FAX compression or decompression channel.
*/
typedef struct
{
    /* "Background" information about the FAX, which can be stored in a TIFF file. */
    /*! \brief The vendor of the machine which produced the TIFF file. */ 
    const char      *vendor;
    /*! \brief The model of machine which produced the TIFF file. */ 
    const char      *model;
    /*! \brief The local ident string. */ 
    const char      *local_ident;
    /*! \brief The remote end's ident string. */ 
    const char      *far_ident;
    /*! \brief The FAX sub-address. */ 
    const char      *sub_address;
    /*! \brief The text which will be used in FAX page header. No text results
               in no header line. */
    const char      *header_info;

    /*! \brief The type of compression used between the FAX machines. */
    int             line_encoding;
    /*! \brief The minimum number of bits per scan row. This is a timing thing
               for hardware FAX machines. */
    int             min_scan_line_bits;
    
    int             output_compression;
    int             output_t4_options;

    time_t          page_start_time;

    int             bytes_per_row;
    int             image_size;
    int             image_buffer_size;
    uint8_t         *image_buffer;

    TIFF            *tiff_file;
    const char      *file;
    int             start_page;
    int             stop_page;

    int             pages_transferred;
    int             pages_in_file;
    /*! Column-to-column (X) resolution in pixels per metre. */
    int             x_resolution;
    /*! Row-to-row (Y) resolution in pixels per metre. */
    int             y_resolution;
    /*! Width of the current page, in pixels. */
    int             image_width;
    /*! Current pixel row number. */
    int             row;
    /*! Total pixel rows in the current page. */
    int             image_length;
    /*! The current number of consecutive bad rows. */
    int             curr_bad_row_run;
    /*! The longest run of consecutive bad rows seen in the current page. */
    int             longest_bad_row_run;
    /*! The total number of bad rows in the current page. */
    int             bad_rows;

    /* Decode state */
    uint32_t        bits_to_date;
    int             bits;

    /*! \brief This variable is set if we are treating the current row as a 2D encoded
               one. */
    int             row_is_2d;
    int             its_black;
    int             row_len;
    /*! \brief This variable is used to record the fact we have seen at least one EOL
               since we started decoding. We will not try to interpret the received
               data as an image until we have seen the first EOL. */
    int             first_eol_seen;
    /*! \brief This variable is used to count the consecutive EOLS we have seen. If it
               reaches six, this is the end of the image. */
    int             consecutive_eols;

    /*! \brief B&W runs for reference line */
    uint32_t        *ref_runs;
    /*! \brief B&W runs for current line */
    uint32_t        *cur_runs;

    uint32_t        *pa;
    uint32_t        *pb;
    int             a0;
    int             b1;
    /*! \brief The length of the current run of black or white. */
    int             run_length;
    int             black_white;

    uint32_t        data;
    int             bit;

    /*! \brief A point into the image buffer indicating where the last row begins */
    int             last_row_starts_at;
    /*! \brief A point into the image buffer indicating where the current row begins */
    int             row_starts_at;
    
    /* Encode state */

    /*! Pointer to the buffer for the current pixel row. */
    uint8_t         *row_buf;
    
    int             bit_pos;
    int             bit_ptr;

    /*! \brief The reference pixel row for 2D encoding. */
    uint8_t         *ref_row_buf;
    /*! \brief The maximum contiguous rows that will be 2D encoded. */
    int             max_rows_to_next_1d_row;
    /*! \brief Number of rows left that can be 2D encoded, before a 1D encoded row
               must be used. */
    int             rows_to_next_1d_row;
    /*! \brief The minimum number of encoded bits per row. */
    int             min_row_bits;
    /*! \brief The current number of bits in the current encoded row. */
    int             row_bits;

    /*! \brief Error and flow logging control */
    logging_state_t logging;
} t4_state_t;

/*!
    T.4 FAX compression/decompression statistics.
*/
typedef struct
{
    /*! \brief The number of pages transferred so far. */
    int pages_transferred;
    /*! \brief The number of pages in the file (<0 if unknown). */
    int pages_in_file;
    /*! \brief The number of horizontal pixels in the most recent page. */
    int width;
    /*! \brief The number of vertical pixels in the most recent page. */
    int length;
    /*! \brief The number of bad pixel rows in the most recent page. */
    int bad_rows;
    /*! \brief The largest number of bad pixel rows in a block in the most recent page. */
    int longest_bad_row_run;
    /*! \brief The horizontal resolution of the page in pixels per metre */
    int x_resolution;
    /*! \brief The vertical resolution of the page in pixels per metre */
    int y_resolution;
    /*! \brief The type of compression used between the FAX machines */
    int encoding;
    /*! \brief The size of the image, in bytes */
    int image_size;
} t4_stats_t;
    
#if defined(__cplusplus)
extern "C" {
#endif

/*! \brief Allocate a T.4 transmit handling context, and
           initialise it.
    \param file The name of the file to be received.
    \param output_encoding The output encoding.
    \return The T.4 context, or NULL. */
t4_state_t *t4_rx_create(const char *file, int output_encoding);

/*! \brief Prepare for reception of a document.
    \param s The T.4 context.
    \param file The name of the file to be received.
    \param output_encoding The output encoding.
    \return 0 for success, otherwise -1. */
int t4_rx_init(t4_state_t *s, const char *file, int output_encoding);

/*! \brief Prepare to receive the next page of the current document.
    \param s The T.4 context.
    \return zero for success, -1 for failure. */