Ubuntu Manpage: TIFFRGBAImageOK, TIFFRGBAImageBegin, TIFFRGBAImageGet, TIFFRGBAImageEnd

Provided by: libtiff-dev_4.3.0-6ubuntu0.10_amd64

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_t* raster, uint32_t width , uint32_t 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_t* raster,
           uint32_t x, uint32_t y, uint32_t w, uint32_t h,
           int32_t fromskew, int32_t 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.