TIFFReadScanline(3T)		     Image Format Library C++ Reference	Manual

NAME    [Toc]    [Back]

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

SYNOPSIS    [Toc]    [Back]

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

DESCRIPTION    [Toc]    [Back]

     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    [Toc]    [Back]

     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 automatically
     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    [Toc]    [Back]

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

DIAGNOSTICS    [Toc]    [Back]

     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    [Toc]    [Back]

     Reading subsampled	YCbCR data does	not work correctly because, for
     PlanarConfiguration=2 the size of a scanline is not calculated on a persample
 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.





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TIFFReadScanline(3T)		     Image Format Library C++ Reference	Manual

SEE ALSO    [Toc]    [Back]

     libtiff(3T), TIFFOpen(3T),	TIFFReadEncodedStrip(3T), TIFFReadRawStrip(3T)


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