Tribblix: manual page: TIFFReadScanline.3tiff

TIFFReadScanline(3TIFF) TIFFReadScanline(3TIFF)

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_t row, tsample_t
sample)

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
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

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

DIAGNOSTICS

All error messages are directed to the TIFFError(3TIFF) 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
PlanarConfiguration=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.