TIFFRGBAImage
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 different characteristics: bits/sam-
ple, 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 pro-
cessed 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 TIFFRGBAIm-
ageGet 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 col-
orimetry information present in the directory.
The paramater stopOnError specifies how to act if an error is encoun-
tered 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: PlanarCon-
figuration=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 follow-
ing 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 fla-
vors 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 applica-
tion.
NOTES
Samples must be either 1, 2, 4, 8, or 16 bits. Colorimetric sam-
ples/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 miss-
ing 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 mem-
ory 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 BitsPer-
Sample, SamplesPerPixel, and PhotometricInterpretation) that can not be
handled.
No space for B&W mapping table. There was insufficient memory to allo-
cate 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.
BUGS
Orientations other than bottom-left, or top-left are not handled cor-
rectly.
SEE ALSO
libtiff(3T), TIFFOpen(3T), TIFFReadRGBAImage(3T), TIFFReadRGBAS-
trip(3T), TIFFReadRGBATile(3T)
October 15, 1995 TIFFRGBAImage(3T)
