2008.05.19 04:51 "[Tiff] RE: Tiff Digest, Vol 48, Issue 6", by Garry Petrie

Interesting comments concerning RGB inputs. I assumed there were tags in the file declaring it as a BW image at least. Or is this left to me, to call the correct procedure to interpret BW images? Obviously, one is not interested in directly viewing a digital elevation model encoded in a geotiff as a raw image in Photoshop, but rather post process the file for the information it contains. The seamless.usgs.gov web site, after you drill down to the area of interest, allows you to open a download dialog. In that dialog box, there is a choice to change the default data type (ArcGrid) to geotiff. I was kind of hoping with all the experience using geotiff and remote sensing, that someone on this list had experience using this data source. I will try and see what GDAL can do.

Garry

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An application using libtiff can use it to retrieve 32 bit float samples. The problem is that 32 bit samples can represent almost anything and there is no one way to create a pleasing 8bit/sample RGB image from it. It is up to the application to decide what to do with the data.

I did not know how to use the seamless.usgs.gov site. I did download a bundle of large files but did not find any TIFF files therein.

Bob

> Message: 3
> Date: Sun, 18 May 2008 12:59:24 +0400
> From: Andrey Kiselev <dron@ak4719.spb.edu>
> Subject: Re: [Tiff] 32 bit samples
> To: tiff@lists.maptools.org
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> 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