TIFFReadScanline

Section: Misc. Reference Manual Pages (3T)
Updated: December 16, 1991
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NAME

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

SYNOPSIS

#include <tiffio.h>
int TIFFReadScanline(TIFF* tif, u_char* buf, u_int row, u_int sample)

DESCRIPTION

Read the data for the specified row into the (user supplied) data buffer buf. The data are returned decompressed and, typically, 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). TIFFReadScanline returns -1 if it detects an error; otherwise 1 is returned.

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 always done if the FillOrder tag is opposite to the native machine bit order. Byte swapping of 16- and 32-bit samples is automatically done when Compression=1 (``no compression''), but otherwise is left to the decompression algorithms (which should generate decompressed data in the native byte ordering of the machine).

In C++ the sample parameter defaults to 0.

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 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.

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