Provided by: libtiff-dev_4.5.1+git230720-1ubuntu1.2_amd64 
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_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 × 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 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 -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 TIFFErrorExtR() 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), TIFFReadRGBAStrip (3tiff), TIFFReadRGBATile
(3tiff), libtiff (3tiff)
AUTHOR
LibTIFF contributors
COPYRIGHT
1988-2024, LibTIFF contributors