2003.11.03 16:01 "[Tiff] Re: ask for suggestions....", by Frank Warmerdam
Would you please attatch the TIFFReadRGBATile() manual pages as a document? There are a lot of wrong words of the mail you sent to me. I think that something wong....
Sorry... it was still formatted for terminal window output. I have reformatted and attached a more readable version.
Would you like tell me what's the difference between TIFFReadTile and TIFFReadRGBATile? I tried them both, but neither works. If I used the TIFFReadTile for reading the tile image, then is is right that the buffer size should be (tilewidth* tileLength *3)*uint32? I have noticed that TIFFGetR, TIFFGetG, and TIFFGetB is used in the condition of TIFFReadRGBATile, then can I use TIFFGetR, TIFFGetG, and TIFFGetB to read the data out read by TIFFReadTile?
TIFFReadTile() reads the raw data, while TIFFReadRGBATile() interpretes various information about color modes, sample size and tries to produce a normalized RGBA output image suitable for viewing.
They both work. You just haven't gotten a handle on how to work with them.
You cannot use TIFFGetR() and similar macros with the output of TIFFReadTile(). You have to interprete data from it in terms of the other tag information. If you just want a picture you can do something with you are likeliy better off using TIFFReadRGBATile().
I would stress the need to review all available reference material. I am not personally keen on talking you through the more esoteric issues of imagery programming in C.
Best regards,
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up | Frank Warmerdam, warmerdam@pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush | Geospatial Programmer for Rent
TIFFReadRGBATile(3T) TIFFReadRGBATile(3T)
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(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. Colorimetric sam-
ples/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 TIFFRGBAIm-
age(3T) facilities. It�s main advantage over the similar TIFFReadRG-
BAImage() 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. Other-
wise, 0 is returned if an error was encountered.
DIAGNOSTICS
All error messages are directed to the TIFFError(3T) 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 miss-
ing 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 mem-
ory 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 BitsPer-
Sample, SamplesPerPixel, and PhotometricInterpretation) that TIFFRead-
RGBAImage can not handle.
No space for B&W mapping table. There was insufficient memory to allo-
cate 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.
BUGS
Orientations other than bottom-left, or top-left are not handled cor-
rectly.
SEE ALSO
libtiff(3T), TIFFOpen(3T), TIFFRGBAImage(3T), TIFFReadRGBAImage(3T),
TIFFReadRGBAStrip(3T)
December 10, 1998 TIFFReadRGBATile(3T)