	addtiffo 1.0
	============

The addtiffo utility is used to add overview pyramids to an existing 
TIFF or GeoTIFF file.  Some applications can take advantage of these
overviews to accelerate overview display performance of large rasters. 

This release of addtiffo is primarily intended for compatibility testing
with applications, and to see if there is interest in a cleaner release
of the capability ... perhaps incorporation into the libtiff tools 
distribution. 

Please feel free to contact me with questions, or problems.

warmerda@home.com
http://members.home.com/warmerda


Usage
-----

Usage: addtiffo [-subifd] tiff_filename [resolution_reductions]

Example:
 % addtiffo abc.tif 2 4 8 16

The numeric arguments are the list of reduction factors to 
generate.  In this example a 1/2, 1/4 1/8 and 1/16 



Limitations
-----------

See tif_overview.cpp for up to date details. 

  o RawBlockedImage will create temporary files in the current directory
    to cache the overviews so it doesn't have to hold them all in memory.
    If the application crashes these will not be deleted (*.rbi).

  o Currently only images with bits_per_sample of a multiple of eight
    will work.

  o The downsampler currently just takes the top left pixel from the
    source rectangle.  Eventually sampling options of averaging, mode, and
    ``center pixel'' should be offered.

  o The code will attempt to use the same kind of compression,
    photometric interpretation, and organization as the source image, but
    it doesn't copy geotiff tags to the reduced resolution images.

  o Reduced resolution overviews for multi-sample files will currently
    always be generated as PLANARCONFIG_SEPARATE.  This could be fixed
    reasonable easily if needed to improve compatibility with other
    packages.  Many don't properly support PLANARCONFIG_SEPARATE. 

  o Overviews are always written as appended IFDs, rather than using the
    ``tree of tree's'' approach using the SUBIFD tag.  I wanted to implement
    both, but it isn't currently easy to add a SUBIFD tag to an existing
    main tiff IFD with libtiff.  I hope to try this again later. 


TIFF File Tags
--------------

The results of running addtiffo on a 1024x1024 tiled greyscale file 
with the arguments ``2 4 8 16'' is to add four additional TIFF directories
appended on the file with the SUBFILETYPE flag to 0x1 indicating the extra
items are reduced resolution images. 

The tiffinfo output of such a file might look like this:

TIFF Directory at offset 0x118008
  Image Width: 1024 Image Length: 1024
  Tile Width: 256 Tile Length: 112
  Bits/Sample: 8
  Compression Scheme: none
  Photometric Interpretation: min-is-black
  Samples/Pixel: 1
  Planar Configuration: single image plane
TIFF Directory at offset 0x15e1d2
  Subfile Type: reduced-resolution image (1 = 0x1)
  Image Width: 512 Image Length: 512
  Tile Width: 256 Tile Length: 112
  Bits/Sample: 8
  Compression Scheme: none
  Photometric Interpretation: min-is-black
  Samples/Pixel: 1
  Planar Configuration: separate image planes
TIFF Directory at offset 0x1732b8
  Subfile Type: reduced-resolution image (1 = 0x1)
  Image Width: 256 Image Length: 256
  Tile Width: 256 Tile Length: 112
  Bits/Sample: 8
  Compression Scheme: none
  Photometric Interpretation: min-is-black
  Samples/Pixel: 1
  Planar Configuration: separate image planes
TIFF Directory at offset 0x17a366
  Subfile Type: reduced-resolution image (1 = 0x1)
  Image Width: 128 Image Length: 128
  Tile Width: 128 Tile Length: 112
  Bits/Sample: 8
  Compression Scheme: none
  Photometric Interpretation: min-is-black
  Samples/Pixel: 1
  Planar Configuration: separate image planes
TIFF Directory at offset 0x17b40c
  Subfile Type: reduced-resolution image (1 = 0x1)
  Image Width: 64 Image Length: 64
  Tile Width: 64 Tile Length: 64
  Bits/Sample: 8
  Compression Scheme: none
  Photometric Interpretation: min-is-black
  Samples/Pixel: 1
  Planar Configuration: separate image planes


Building
--------

You will need a C, and C++ compiler.  You will need to have libtiff already
built and installed.  The provided Makefile should work on most Unix systems.
A similar file will be needed for Windows, but is not provided. 

The CFLAGS and LIBS macros in the Makefile will have to be updated to 
point to the correct location of the libtiff include files, and library.


Credits
-------

 o Intergraph Corporation for partially funding the work. 

 o Global Geomatics for partially funding reorganization of the overview
   building ability as a separate utility.

 o Orrin Long, and Ed Grissom of Intergraph for explaining what needed to 
   be done. 

 o Max Martinez of Erdas for his discussion of external overviews. 

 o Frank Warmerdam for writing the bulk of the code. 

 o Sam Leffler since this only exists because of his libtiff. 
