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       - read and decode an image into a raster

       #include	<tiffio.h>

       typedef	unsigned  char	TIFFRGBValue;  typedef	struct	_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/sam-
       ple, samples/pixel, photometric,	etc.  Decoding state  is  encapsulated
       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 particular application's needs	by in-
       stalling	custom routines	that manipulate	image data according to	appli-
       cation requirements.

       The  default usage for these routines is: check if an image can be pro-
       cessed using TIFFRGBAImageOK, 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  TIFFRGBAIm-
       ageGet 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 origin  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 ac-
       cess  individual	 samples.  Images without Associated Alpha matting in-
       formation 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  col-
       orimetry	information present in the directory.

       The  parameter  stopOnError specifies how to act	if an error is encoun-
       tered while reading the image.  If stopOnError is non-zero, then	an er-
       ror  will terminate the operation; otherwise TIFFRGBAImageGet will con-
       tinue 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: PlanarCon-
       figuration=1 (packed  samples),	and  PlanarConfiguration=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 reference 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 follow-
       ing 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

       The  TIFFRGBAImage  routines support the	most commonly encountered fla-
       vors of TIFF.  It is possible to	extend this support by overriding  the
       ``get  method''	invoked	 by  TIFFRGBAImageGet 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 applica-

       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 Ex-

       Palette image colormaps that appear to be incorrectly written as	 8-bit
       values are automatically	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(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  re-
       quired 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 can	not be

       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.

       TIFFOpen(3TIFF),	    TIFFReadRGBAImage(3TIFF),	 TIFFReadRGBAImageOri-
       ented(3TIFF),	TIFFReadRGBAStrip(3TIFF),     TIFFReadRGBATile(3TIFF),

       Libtiff library home page:

libtiff			       October 29, 2004		  TIFFRGBAImage(3TIFF)


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