TIFFReadRGBATile(3TIFF) TIFFReadRGBATile(3TIFF)

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_t x, uint32_t y, uint32_t
*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.simplesystems.org/libtiff/

libtiff December 10, 1998 TIFFReadRGBATile(3TIFF)