TIFFReadScanline

TIFFReadScanline(3T)                                      TIFFReadScanline(3T)



NAME
       TIFFReadScanline - read and decode a scanline of data from an open TIFF
       file

SYNOPSIS
       #include <tiffio.h>
       int TIFFReadScanline(TIFF* tif, tdata_t buf, uint32 row, tsample_t sam-
       ple)

DESCRIPTION
       Read  the  data  for  the  specified  row into the (user supplied) data
       buffer buf.  The data are returned  decompressed  and,  in  the  native
       byte-  and  bit-ordering, but are otherwise packed (see further below).
       The buffer must be large enough to hold an  entire  scanline  of  data.
       Applications  should  call the routine TIFFScanlineSize to find out the
       size (in bytes) of a scanline buffer.  The row parameter is always used
       by  TIFFReadScanline;  the  sample  parameter  is used only if data are
       organized in separate planes (PlanarConfiguration=2).

NOTES
       The library attempts to hide bit- and byte-ordering differences between
       the  image  and  the  native  machine  by converting data to the native
       machine order.  Bit reversal is done if the FillOrder tag  is  opposite
       to  the native machine bit order.  16- and 32-bit samples are automati-
       cally byte-swapped if the file was written with a byte  order  opposite
       to the native machine byte order,

       In C++ the sample parameter defaults to 0.

RETURN VALUES
       TIFFReadScanline  returns  -1  if  it  detects an error; otherwise 1 is
       returned.

DIAGNOSTICS
       All error messages are directed to the TIFFError(3T) routine.

       Compression  algorithm  does  not  support  random  access.   Data  was
       requested in a non-sequential order from a file that uses a compression
       algorithm and that has RowsPerStrip greater than one.  That is, data in
       the image is stored in a compressed form, and with multiple rows packed
       into a strip.  In this case, the library does not support random access
       to  the  data.  The data should either be accessed sequentially, or the
       file should be converted so that each strip is made up of  one  row  of
       data.

BUGS
       Reading subsampled YCbCR data does not work correctly because, for Pla-
       narConfiguration=2 the size of a scanline is not calculated on  a  per-
       sample basis, and for PlanarConfiguration=1 the library does not unpack
       the block-interleaved samples; use the strip- and tile-based interfaces
       to read these formats.

SEE ALSO
       libtiff(3T),   TIFFOpen(3T),   TIFFReadEncodedStrip(3T),   TIFFReadRaw-
       Strip(3T)



                               October 15, 1995           TIFFReadScanline(3T)