TIFFRGBAIMAGE(3tiff) LibTIFF TIFFRGBAIMAGE(3tiff)
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:
o check if an image can be processed using TIFFRGBAImageOK()
o construct a decoder state block using TIFFRGBAImageBegin()
o read and decode an image into a target raster using
TIFFRGBAImageGet(), and then
o 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 x 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 x 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. An example for a "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(3), TIFFReadRGBAImage(3), TIFFReadRGBAStrip(3),
TIFFReadRGBATile(3), libtiff(3)
AUTHOR
LibTIFF contributors
COPYRIGHT
1988-2022, LibTIFF contributors
4.6 October 9, 2023 TIFFRGBAIMAGE(3tiff)
tiff 4.6.0 - Generated Sat Oct 14 07:12:44 CDT 2023