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TIFFRGBAImage

NAME

SYNOPSIS

DESCRIPTION

ALTERNATE RASTER FORMATS

SIMULTANEOUS RASTER STORE AND DISPLAY

SUPPORTING ADDITIONAL TIFF FORMATS

NOTES

RETURN VALUES

DIAGNOSTICS

SEE ALSO

NAME

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TIFFRGBAImageOK, TIFFRGBAImageBegin, TIFFRGBAImageGet,

TIFFRGBAImageEnd − read and decode an image into a

raster

SYNOPSIS

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#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

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The routines described here provide a high-level

interface through which <small>TIFF</small> images may be

read into memory. Images may be strip- or tile-based and

have a variety of different characteristics: bits/sample,

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 processed 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

TIFFRGBAImageGet 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,

<small>CMYK</small> , and YCbCr images are converted to

<small>RGB</small> transparently. Raster pixels are returned

uncorrected by any colorimetry information present in the

directory.

The parameter stopOnError specifies how to act if

an error is encountered 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

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To use the core support for reading and processing

<small>TIFF</small> 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 <small>ABGR</small> pixel format.

Two different routines are used according to the physical

organization of the image data in the file:

PlanarConfiguration=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

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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 following 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

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The TIFFRGBAImage routines support the most

commonly encountered flavors of <small>TIFF.</small> It is

possible to extend this support by overriding the

‘‘get method’’ invoked by

TIFFRGBAImageGet to read <small>TIFF</small> 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 application.

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.

RETURN VALUES

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All routines return 1 if the operation was successful.

Otherwise, 0 is returned if an error was encountered and

stopOnError is zero.

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 can not be

handled.

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), TIFFReadRGBAImage(3TIFF),

TIFFReadRGBAImageOriented(3TIFF),

TIFFReadRGBAStrip(3TIFF),

TIFFReadRGBATile(3TIFF), libtiff(3TIFF)

Libtiff library home page:

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