TIFFReadRGBATile(3TIFF)                                TIFFReadRGBATile(3TIFF)



NAME
       TIFFReadRGBATile - read and decode an image tile into a fixed-format
       raster

SYNOPSIS
       #include <tiffio.h>

       #define TIFFGetR(abgr)   ((abgr) & 0xff)
       #define TIFFGetG(abgr)   (((abgr) >> 8) & 0xff)
       #define TIFFGetB(abgr)   (((abgr) >> 16) & 0xff)
       #define TIFFGetA(abgr)   (((abgr) >> 24) & 0xff)

       int TIFFReadRGBATile(TIFF *tif, uint32 x, uint32 y, uint32 *raster)

DESCRIPTION
       TIFFReadRGBATile reads a single tile of a tile-based image into memory,
       storing the result in the user supplied RGBA raster.  The raster is
       assumed to be an array of width times length 32-bit entries, where
       width is the width of a tile (TIFFTAG_TILEWIDTH) and length is the
       height of a tile (TIFFTAG_TILELENGTH).


       The x and y values are the offsets from the top left corner to the top
       left corner of the tile to be read.  They must be an exact multiple of
       the tile width and length.


       Note that the raster is assume to be organized such that the pixel at
       location (x,y) is raster[y*width+x]; with the raster origin in the
       lower-left hand corner of the tile. That is bottom to top organization.
       Edge tiles which partly fall off the image will be filled out with
       appropriate zeroed areas.


       Raster pixels are 8-bit packed red, green, blue, alpha samples. The
       macros TIFFGetR, TIFFGetG, TIFFGetB, and TIFFGetA should be used to
       access individual samples. Images without Associated Alpha matting
       information have a constant Alpha of 1.0 (255).

       See the TIFFRGBAImage(3TIFF) page for more details on how various image
       types are converted to RGBA values.

NOTES
       Samples must be either 1, 2, 4, 8, or 16 bits. Colorimetric
       samples/pixel must be either 1, 3, or 4 (i.e.  SamplesPerPixel minus
       ExtraSamples).

       Palette image colormaps that appear to be incorrectly written as 8-bit
       values are automatically scaled to 16-bits.

       TIFFReadRGBATile is just a wrapper around the more general
       TIFFRGBAImage(3TIFF) facilities.  It's main advantage over the similar
       TIFFReadRGBAImage() function is that for large images a single buffer
       capable of holding the whole image doesn't need to be allocated, only
       enough for one tile.  The TIFFReadRGBAStrip() function does a similar
       operation for stripped images.

RETURN VALUES
       1 is returned if the image was successfully read and converted.
       Otherwise, 0 is returned if an error was encountered.

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

       Sorry, can not handle %d-bit pictures.  The image had BitsPerSample
       other than 1, 2, 4, 8, or 16.

       Sorry, can not handle %d-channel images.  The image had SamplesPerPixel
       other than 1, 3, or 4.

       Missing needed "PhotometricInterpretation" tag.  The image did not have
       a tag that describes how to display the data.

       No "PhotometricInterpretation" tag, assuming RGB.  The image was
       missing a tag that describes how to display it, but because it has 3 or
       4 samples/pixel, it is assumed to be RGB.

       No "PhotometricInterpretation" tag, assuming min-is-black.  The image
       was missing a tag that describes how to display it, but because it has
       1 sample/pixel, it is assumed to be a grayscale or bilevel image.

       No space for photometric conversion table.  There was insufficient
       memory for a table used to convert image samples to 8-bit RGB.

       Missing required "Colormap" tag.  A Palette image did not have a
       required Colormap tag.

       No space for tile buffer.  There was insufficient memory to allocate an
       i/o buffer.

       No space for strip buffer.  There was insufficient memory to allocate
       an i/o buffer.

       Can not handle format.  The image has a format (combination of
       BitsPerSample, SamplesPerPixel, and PhotometricInterpretation) that
       TIFFReadRGBAImage can not handle.

       No space for B&W mapping table.  There was insufficient memory to
       allocate a table used to map grayscale data to RGB.

       No space for Palette mapping table.  There was insufficient memory to
       allocate a table used to map data to 8-bit RGB.

SEE ALSO
       TIFFOpen(3TIFF), TIFFRGBAImage(3TIFF), TIFFReadRGBAImage(3TIFF),
       TIFFReadRGBAStrip(3TIFF), libtiff(3TIFF)

       Libtiff library home page: http://www.remotesensing.org/libtiff/



libtiff                        December 10, 1998       TIFFReadRGBATile(3TIFF)
