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<title>TIFFReadRGBATile</title>

TIFFReadRGBATile

NAME

SYNOPSIS

DESCRIPTION

NOTES

RETURN VALUES

DIAGNOSTICS

SEE ALSO

NAME

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TIFFReadRGBATile − read and decode an image tile

into a fixed-format raster

SYNOPSIS

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#include <tiffio.h>

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#define TIFFGetR(abgr)

((abgr) & 0xff)

#define TIFFGetG(abgr)

(((abgr) >> 8) & 0xff)

#define TIFFGetB(abgr)

(((abgr) >> 16) & 0xff)

#define TIFFGetA(abgr)

(((abgr) >> 24) & 0xff)

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int TIFFReadRGBATile(TIFF *tif,

uint32 x, uint32 y, uint32

*raster)

DESCRIPTION

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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

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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

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1 is returned if the image was successfully read and

converted. Otherwise, 0 is returned if an error was

encountered.

DIAGNOSTICS

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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 <small>RGB.</small>

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 <small>RGB.</small>

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 <small>RGB.</small>

No space for Palette mapping table. There was

insufficient memory to allocate a table used to map data to

8-bit <small>RGB.</small>

SEE ALSO

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TIFFOpen(3TIFF), TIFFRGBAImage(3TIFF),

TIFFReadRGBAImage(3TIFF),

TIFFReadRGBAStrip(3TIFF), libtiff(3TIFF)

Libtiff library home page:

http://www.remotesensing.org/libtiff/