TIFFRGBAImage(3T) Image Format Library C++ Reference Manual
NAME
TIFFRGBAImage - 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.
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TIFFRGBAImage(3T) Image Format Library C++ Reference Manual
The paramater 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.
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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).
Palettte 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(3T) 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.
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TIFFRGBAImage(3T) Image Format Library C++ Reference Manual
No space for Palette mapping table. There was insufficient memory to
allocate a table used to map data to 8-bit RGB.
BUGS
Orientations other than bottom-left, or top-left are not handled
correctly.
SEE ALSO
libtiff(3T), TIFFOpen(3T), TIFFReadRGBAImage(3T)
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