TIFFReadRGBATile(3T)TIFFReadRGBATile(3T)NAMETIFFReadRGBATile - read and decode an image tile into a
fixed-format raster
SYNOPSIS
#include <tiffio.h>
#define TIFFGetR(abgr) ((abgr) & 0xff)
#define TIFFGetG(abgr) (((abgr) >> 8) & 0xff)
#define TIFFGetB(abgr) (((abgr) >> 16) & 0xff)
#define TIFFGetA(abgr) (((abgr) >> 24) & 0xff)
int TIFFReadRGBATile(TIFF* tif, uint32 x, uint32 y, uint32 * raster )
DESCRIPTIONTIFFReadRGBATile reads a single tile of a tile-based image
into memory, storing the result in the user supplied RGBA
raster. The raster is assumed to be an array of width
times length 32-bit entries, where width is the width of a
tile (TIFFTAG_TILEWIDTH) and length is the height of a
tile (TIFFTAG_TILELENGTH).
The x and y values are the offsets from the top left cor
ner to the top left corner of the tile to be read. They
must be an exact multiple of the tile width and length.
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 of the tile.
That is bottom to top organization. Edge tiles which
partly fall off the image will be filled out with appro
priate zeroed areas.
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).
See the TIFFRGBAImage(3T) page for more details on how
various image types are converted to RGBA values.
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).
Palette image colormaps that appear to be incorrectly
written as 8-bit values are automatically scaled to
16-bits.
TIFFReadRGBATile is just a wrapper around the more general
TIFFRGBAImage(3T) facilities. It's main advantage over
the similar TIFFReadRGBAImage() function is that for large
images a single buffer capable of holding the whole image
doesn't need to be allocated, only enough for one tile.
The TIFFReadRGBAStrip() function does a similar operation
for stripped images.
RETURN VALUES
1 is returned if the image was successfully read and
converted. Otherwise, 0 is returned if an error was
encountered.
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
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 TIFFReadRGBAImage can not handle.
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), TIFFRGBAImage(3T), TIFFReadRG_
BAImage(3T), TIFFReadRGBAStrip(3T)
December 10, 1998 TIFFReadRGBATile(3T)
