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TIFFRGBAImage(3T)								TIFFRGBAImage(3T)

       TIFFRGBAImage - read and decode an image into a raster

       #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);

       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  paramater  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.

       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.

       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);
		lrectwrite(0, y, w-1, y+h-1, raster);

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

       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.

       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).

       Palettte image colormaps that appear to be incorrectly written as 8-bit values  are  auto-
       matically scaled to 16-bits.

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

       All error messages are directed to the TIFFError(3T) 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

       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.

       Orientations other than bottom-left, or top-left are not handled correctly.

       libtiff(3T),   TIFFOpen(3T),   TIFFReadRGBAImage(3T),  TIFFReadRGBAStrip(3T),  TIFFReadRG-

					 October 15, 1995			TIFFRGBAImage(3T)
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