2008.05.18 08:59 "Re: [Tiff] 32 bit samples", by Andrey Kiselev

Garry,

On Sat, May 17, 2008 at 09:34:25AM -0700, Garry Petrie wrote:

This web app can produce geotiff files containing digital elevation data for
any place in the world using data from the space shuttle SAR mission. The
format of the tiff portion of the file contains 32 bit samples, not sure if
they are longs or short floats.

There is a special tag for that, called "SampleFormat". It denotes the dat type.

Using libtiff I get the message about not
being able to handle 32bit samples from getimage. I know the web site
produces good image files, as I have been able to view the files with
AdobePS. I peaked at alpha 4.0 and it seems to have the same critical code
as 3.8.2. Are there great obstacles in enabling this function? I am willing
to spend some time with the code, but I don't want to become an expert.

Uor mistake is that you are trying to use RGBA interface of libtiff which can be used for simple images only (1-3 channels, integers, <8 bit in depth). No way to read complex datasets with this API. You should either use a low-level libtiff API or some spicialized software which hides this low-level details from you. GDAL (http://www.gdal.org) will do it for you. Also take a look on OpenEV viewer, because Photoshop is not a suitable tool to deal with georeferenced images.

Best regards,

Andrey

--
Andrey V. Kiselev
ICQ# 26871517