NAME¶
TIFFReadRGBATile - 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)
DESCRIPTION¶
TIFFReadRGBATile 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 corner 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 appropriate 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(3TIFF) 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. Colorimetric samples/pixel must
be either 1, 3, or 4 (i.e.
SamplesPerPixel 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(3TIFF) 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(3TIFF) 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
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 insufficient memory to
allocate a table used to map data to 8-bit
RGB.
SEE ALSO¶
TIFFOpen(3TIFF),
TIFFRGBAImage(3TIFF),
TIFFReadRGBAImage(3TIFF),
TIFFReadRGBAStrip(3TIFF),
libtiff(3TIFF)
Libtiff library home page:
http://www.remotesensing.org/libtiff/