TIFFRGBAImage(3T)TIFFRGBAImage(3T)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 differ-
ent characteristics: bits/sample, samples/pixel, photomet-
ric, etc. Decoding state is encapsulated in a TIFFRGBAIm-
age structure making it possible to capture state for mul-
tiple images and quickly switch between them. The target
raster format can be customized to a particular applica-
tion'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 TIFFRGBAIm-
ageGet, 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
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TIFFRGBAImage(3T)TIFFRGBAImage(3T)
sample values. Palette, grayscale, bilevel, CMYK, and
YCbCr images are converted to RGB transparently. Raster
pixels are returned uncorrected by any colorimetry infor-
mation present in the directory.
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; oth-
erwise 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 TIFFRGBAIm-
ageBegin 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 dis-
play.
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 TIFFRGBAIm-
ageBegin 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);
}
}
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TIFFRGBAImage(3T)TIFFRGBAImage(3T)
(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. Colorimet-
ric samples/pixel must be either 1, 3, or 4 (i.e. Sam-
plesPerPixel 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) rou-
tine.
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 sam-
ples to 8-bit RGB.
Missing required "Colormap" tag. A Palette image did not
October 15, 1995 3
TIFFRGBAImage(3T)TIFFRGBAImage(3T)
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 (combina-
tion of BitsPerSample, SamplesPerPixel, and PhotometricIn-
terpretation) 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 insuffi-
cient 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 ALSOlibtiff(3T), TIFFOpen(3T), TIFFReadRGBAImage(3T), TIFF-
ReadRGBAStrip(3T), TIFFReadRGBATile(3T)
October 15, 1995 4
