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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/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
       installing custom routines that	manipulate  image  data	 according  to
       application 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
       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  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
       error  will  terminate  the  operation; otherwise 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: 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.

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 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);
	    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 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‐
       tion.

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.

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 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 can not be
       handled.

       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),	    TIFFReadRGBAImage(3TIFF),	 TIFFReadRGBAImageOri‐
       ented(3TIFF),	TIFFReadRGBAStrip(3TIFF),     TIFFReadRGBATile(3TIFF),
       libtiff(3TIFF)

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

libtiff			       October 29, 2004		  TIFFRGBAImage(3TIFF)
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