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_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.
SEE ALSO
TIFFOpen(3TIFF),
TIFFReadRGBAImage(3TIFF),
TIFFReadRGBAImageOriented(3TIFF),
TIFFReadRGBAStrip(3TIFF),
TIFFReadRGBATile(3TIFF),
libtiff(3TIFF) Libtiff library home page:
http://www.simplesystems.org/libtiff/libtiff October 29, 2004 TIFFRGBAImage(3TIFF)