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  sam-
       ples/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 TIFFRGBAIm-
       age(3TIFF) facilities.  It's main advantage over the similar  TIFFRead-
       RGBAImage()  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 opera-
       tion for stripped images.

RETURN VALUES

       1 is returned if the image was successfully read and converted.  Other-
       wise, 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  miss-
       ing  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 mem-
       ory 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 BitsPer-
       Sample,  SamplesPerPixel, and PhotometricInterpretation) that TIFFRead-
       RGBAImage can not handle.

       No space for B&W mapping table.  There was insufficient memory to allo-
       cate 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),  TIFF-
       ReadRGBAStrip(3TIFF), libtiff(3TIFF)

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

libtiff                        December 10, 1998       TIFFReadRGBATile(3TIFF)