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lib/Image/Leptonica/Func/pngio.pm  view on Meta::CPAN

    The default is TRUE, which causes pixRead() to strip each 16 bit
    sample down to 8 bps:
     - For 16 bps rgb (16 bps, 3 spp) --> 32 bpp rgb Pix
     - For 16 bps gray (16 bps, 1 spp) --> 8 bpp grayscale Pix
    If the variable is set to FALSE, the 16 bit gray samples
    are saved when read; the 16 bit rgb samples return an error.
    Note: results can be non-deterministic if used with
    multi-threaded applications.

    On systems like windows without fmemopen() and open_memstream(),
    we write data to a temp file and read it back for operations
    between pix and compressed-data, such as pixReadMemPng() and
    pixWriteMemPng().

=head1 FUNCTIONS

=head2 fgetPngResolution

l_int32 fgetPngResolution ( FILE *fp, l_int32 *pxres, l_int32 *pyres )

  fgetPngResolution()

      Input:  stream (opened for read)
              &xres, &yres (<return> resolution in ppi)
      Return: 0 if OK; 0 on error

  Notes:
      (1) If neither resolution field is set, this is not an error;
          the returned resolution values are 0 (designating 'unknown').
      (2) Side-effect: this rewinds the stream.

=head2 freadHeaderPng

l_int32 freadHeaderPng ( FILE *fp, l_int32 *pw, l_int32 *ph, l_int32 *pbps, l_int32 *pspp, l_int32 *piscmap )

  freadHeaderPng()

      Input:  stream
              &w (<optional return>)
              &h (<optional return>)
              &bps (<optional return>, bits/sample)
              &spp (<optional return>, samples/pixel)
              &iscmap (<optional return>)
      Return: 0 if OK, 1 on error

  Notes:
      (1) See readHeaderPng().

=head2 l_pngSetReadStrip16To8

void l_pngSetReadStrip16To8 ( l_int32 flag )

  l_pngSetReadStrip16To8()

      Input:  flag (1 for stripping 16 bpp to 8 bpp on reading;
                    0 for leaving 16 bpp)
      Return: void

=head2 pixReadMemPng

PIX * pixReadMemPng ( const l_uint8 *cdata, size_t size )

  pixReadMemPng()

      Input:  cdata (const; png-encoded)
              size (of data)
      Return: pix, or null on error

  Notes:
      (1) The @size byte of @data must be a null character.

=head2 pixReadStreamPng

PIX * pixReadStreamPng ( FILE *fp )

  pixReadStreamPng()

      Input:  stream
      Return: pix, or null on error

  Notes:
      (1) If called from pixReadStream(), the stream is positioned
          at the beginning of the file.
      (2) To do sequential reads of png format images from a stream,
          use pixReadStreamPng()
      (3) Grayscale-with-alpha pngs (spp = 2) are converted to RGBA
          on read; the returned pix has spp = 4 and equal red, green and
          blue channels.
      (4) spp = 1 with alpha (palette) is converted to RGBA with spp = 4.
      (5) We use the high level png interface, where the transforms are set
          up in advance and the header and image are read with a single
          call.  The more complicated interface, where the header is
          read first and the buffers for the raster image are user-
          allocated before reading the image, works OK for single images,
          but I could not get it to work properly for the successive
          png reads that are required by pixaReadStream().

=head2 pixSetZlibCompression

l_int32 pixSetZlibCompression ( PIX *pix, l_int32 compval )

  pixSetZlibCompression()

      Input:  pix
              compval (zlib compression value)
      Return: 0 if OK, 1 on error

  Notes:
      (1) Valid zlib compression values are in the interval [0 ... 9],
          where, as defined in zlib.h:
            0         Z_NO_COMPRESSION
            1         Z_BEST_SPEED    (poorest compression)
            9         Z_BEST_COMPRESSION
          For the default value, use either of these:
            6         Z_DEFAULT_COMPRESSION
           -1         (resolves to Z_DEFAULT_COMPRESSION)
      (2) If you use the defined constants in zlib.h instead of the
          compression integers given above, you must include zlib.h.

=head2 pixWriteMemPng

l_int32 pixWriteMemPng ( l_uint8 **pdata, size_t *psize, PIX *pix, l_float32 gamma )

  pixWriteMemPng()