TIFFReadRGBATile(3TIFF)                   TIFFReadRGBATile(3TIFF)



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

SYNOPSIS
       #include 

       #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  cor-
       ner  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  appro-
       priate 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.  Colorimet-
       ric  samples/pixel  must  be either 1, 3, or 4 (i.e.  Sam-
       plesPerPixel 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  con-
       verted.   Otherwise, 0 is returned if an error was encoun-
       tered.

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 sam-
       ples 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  (combina-
       tion of BitsPerSample, SamplesPerPixel, and PhotometricIn-
       terpretation) 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  insuffi-
       cient memory to allocate a table used to map data to 8-bit
       RGB.

SEE ALSO
       TIFFOpen(3TIFF),   TIFFRGBAImage(3TIFF),   TIFFReadRGBAIm-
       age(3TIFF), TIFFReadRGBAStrip(3TIFF), libtiff(3TIFF)

       Libtiff    library   home   page:   http://www.remotesens-
       ing.org/libtiff/



libtiff                 December 10, 1998 TIFFReadRGBATile(3TIFF)