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TIFFRGBAImage(3TIFF)							     TIFFRGBAImage(3TIFF)

NAME
       TIFFRGBAImageOK,  TIFFRGBAImageBegin, TIFFRGBAImageGet, TIFFRGBAImageEnd - read and decode
       an image into a raster

SYNOPSIS
       #include <tiffio.h>

       typedef unsigned char TIFFRGBValue; typedef struct _TIFFRGBAImage TIFFRGBAImage;

       int TIFFRGBAImageOK(TIFF *tif, char emsg[1024])
       int TIFFRGBAImageBegin(TIFFRGBAImage *img, TIFF* tif, int stopOnError, char emsg[1024])
       int TIFFRGBAImageGet(TIFFRGBAImage *img, uint32* raster, uint32 width , uint32 height)
       void TIFFRGBAImageEnd(TIFFRGBAImage *img)

DESCRIPTION
       The routines described here provide a high-level interface through which TIFF  images  may
       be  read  into memory.  Images may be strip- or tile-based and have a variety of different
       characteristics: bits/sample, samples/pixel, photometric, etc.  Decoding state is encapsu-
       lated in a TIFFRGBAImage structure making it possible to capture state for multiple images
       and quickly switch between them.  The target raster format can be customized to a particu-
       lar application's needs by installing custom routines that manipulate image data according
       to application requirements.

       The default usage for these routines is: check if an image can be processed using  TIFFRG-
       BAImageOK,  construct  a  decoder state block using TIFFRGBAImageBegin, read and decode an
       image into a target raster  using  TIFFRGBAImageGet,  and  then	release  resources  using
       TIFFRGBAImageEnd.   TIFFRGBAImageGet can be called multiple times to decode an image using
       different state parameters.  If multiple images are to  be  displayed  and  there  is  not
       enough  space  for  each  of the decoded rasters, multiple state blocks can be managed and
       then calls can be made to TIFFRGBAImageGet as needed to display an image.

       The generated raster is assumed to be an array of width times height 32-bit entries, where
       width  must  be	less  than or equal to the width of the image (height may be any non-zero
       size).  If the raster dimensions are smaller than the image, the image data is cropped  to
       the raster bounds.  If the raster height is greater than that of the image, then the image
       data are placed in the lower part of the raster.  (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 ori-
       gin in the lower-left hand corner.)

       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).

       TIFFRGBAImageGet converts non-8-bit images by scaling sample values.  Palette,  grayscale,
       bilevel,  CMYK,	and  YCbCr  images are converted to RGB transparently.	Raster pixels are
       returned uncorrected by any colorimetry information present in the directory.

       The parameter stopOnError specifies how to act if an error is  encountered  while  reading
       the image.  If stopOnError is non-zero, then an error will terminate the operation; other-
       wise TIFFRGBAImageGet will continue processing data until all the  possible  data  in  the
       image have been requested.

ALTERNATE RASTER FORMATS
       To  use	the  core support for reading and processing TIFF images, but write the resulting
       raster data in a different format one need only override the ``put methods'' used to store
       raster  data.   These methods are are defined in the TIFFRGBAImage structure and initially
       setup by TIFFRGBAImageBegin to point to routines that pack raster data in the default ABGR
       pixel  format.	Two different routines are used according to the physical organization of
       the image data in the file: PlanarConfiguration=1 (packed samples),  and  PlanarConfigura-
       tion=2  (separated  samples).   Note that this mechanism can be used to transform the data
       before storing it in the raster.  For example one can convert data to colormap indices for
       display on a colormap display.

SIMULTANEOUS RASTER STORE AND DISPLAY
       It  is  simple  to  display an image as it is being read into memory by overriding the put
       methods as described above for supporting alternate raster formats.  Simply keep a  refer-
       ence to the default put methods setup by TIFFRGBAImageBegin and then invoke them before or
       after each display operation.  For example, the tiffgt(1) utility uses the  following  put
       method to update the display as the raster is being filled:

       static void
       putContigAndDraw(TIFFRGBAImage* img, uint32* raster,
	   uint32 x, uint32 y, uint32 w, uint32 h,
	   int32 fromskew, int32 toskew,
	   unsigned char* cp)
       {
	   (*putContig)(img, raster, x, y, w, h, fromskew, toskew, cp);
	   if (x+w == width) {
	    w = width;
	    if (img->orientation == ORIENTATION_TOPLEFT)
		lrectwrite(0, y-(h-1), w-1, y, raster-x-(h-1)*w);
	    else
		lrectwrite(0, y, w-1, y+h-1, raster);
	   }
       }

       (the original routine provided by the library is saved in the variable putContig.)

SUPPORTING ADDITIONAL TIFF FORMATS
       The  TIFFRGBAImage  routines support the most commonly encountered flavors of TIFF.  It is
       possible to extend this support by overriding the ``get method''  invoked  by  TIFFRGBAIm-
       ageGet  to  read TIFF image data.  Details of doing this are a bit involved, it is best to
       make a copy of an existing get method and modify it to suit the needs of an application.

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 automat-
       ically scaled to 16-bits.

RETURN VALUES
       All routines return 1 if the operation was successful.  Otherwise, 0  is  returned  if  an
       error was encountered and stopOnError is zero.

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, SamplesPer-
       Pixel, and PhotometricInterpretation) that can not be handled.

       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), TIFFReadRGBAImage(3TIFF),  TIFFReadRGBAImageOriented(3TIFF),  TIFFReadRG-
       BAStrip(3TIFF), TIFFReadRGBATile(3TIFF), libtiff(3TIFF)

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

libtiff 				 October 29, 2004		     TIFFRGBAImage(3TIFF)
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