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
       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
       processed 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
       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 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
       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; 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:
       PlanarConfiguration=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
       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 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
       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 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
       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, SamplesPerPixel, 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), TIFFReadRGBAStrip(3TIFF),
       TIFFReadRGBATile(3TIFF), libtiff(3TIFF)

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



libtiff                        October 29, 2004           TIFFRGBAImage(3TIFF)
