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Ytrapaet,<br>
There is no such thing as an 'associated color table' in strict
TIFF meaning. In the specific case of DEM TIFF you have either one of
two cases: 1) a grayscale TIFF that is generated using some sort of
mapping between raw elevation values and grayscale colors. If the
mapping is 1-to-1 which is, of course, normally only possible for 16 or
32 bit grayscale color mode, it can be called "raw" data, since it
allows conversion back to the original values, well, at least with
integer precision. This grayscale TIFFs can be rendered by various
software packages using whatever colorization method they default to or
whatever the user choice is; obviously in case of Photoshop there is no
default and its up to the user to apply whatever gradient they choose
manually 2) a pre-colorized TIFF, basically 2D or 3D rendering of the
DEM data where the raw values are irreversibly replaced by the image
rendition using selected colorization schema. The choice is determined,
say, in ArcGIS by 'Use rendered' checkbox on export. There are, of
course, some other formats (ESRI HDR, for example) that indeed do store
a color table separately, however in any case this is not a kind of
information that Photoshop would render out-of-the-box. Moreover, even
rendering a simple 16-bit graysclae image in Photoshop is not performed
on a 1-1 mapping basis - Adobe has their own way of re-interpreting
values for display purpose and I remember having to dig through Adobe
forums unraveling these mysteries when working on our Geographic Imager
product. In any case, I think Frank is right and indeed it is more of a
Photoshop discussion at this point. If you want, you can contact me
offline or/and send your sample data if you still have any specific
questions.<br>
<br>
ivar<br>
Avenza Systems Inc<br>
<br>
On 23/02/2010 2:46 PM, <a class="moz-txt-link-abbreviated" href="mailto:gdal-dev-request@lists.osgeo.org">gdal-dev-request@lists.osgeo.org</a> wrote:
<blockquote cite="mid:20100223194614.92F2FE01EA1@lists.osgeo.org"
type="cite">
<pre wrap=""><div class="moz-txt-sig">Message: 4
Date: Tue, 23 Feb 2010 14:12:56 -0500
From: Frank Warmerdam <a moz-do-not-send="true"
class="moz-txt-link-rfc2396E" href="mailto:warmerdam@pobox.com"><warmerdam@pobox.com></a>
Subject: Re: [gdal-dev] Re: storing height information in a .tif
rather the grayscale in the tif relying on another file
To: anotherObject <a moz-do-not-send="true"
class="moz-txt-link-rfc2396E" href="mailto:ytrapaet@hotmail.com"><ytrapaet@hotmail.com></a>
Cc: <a moz-do-not-send="true" class="moz-txt-link-abbreviated"
href="mailto:gdal-dev@lists.osgeo.org">gdal-dev@lists.osgeo.org</a>
Message-ID: <a moz-do-not-send="true" class="moz-txt-link-rfc2396E"
href="mailto:4B8428B8.60604@pobox.com"><4B8428B8.60604@pobox.com></a>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
anotherObject wrote:
</div></pre>
<blockquote type="cite" style="color: rgb(0, 0, 0);">
<pre wrap=""><span class="moz-txt-citetags">> </span>Sorry for not being clearer: I started off with a a 32bit tif - however, im
<span class="moz-txt-citetags">> </span>not sure how I can tell if it has an associated color table.
</pre>
</blockquote>
<pre wrap="">Ytrapaet,
Try running gdalinfo against the file and seeing what it reports. Including
a gdalinfo report with your email would make it much easier for us to
give a meaningful reply.
</pre>
<blockquote type="cite" style="color: rgb(0, 0, 0);">
<pre wrap=""><span class="moz-txt-citetags">> </span>Are there both types of tifs? if so how can I convert from one to the other?
</pre>
</blockquote>
<pre wrap="">There are many types of TIFF files. TIFF supports a wide variety of color
models, pixel data types and numbers of bands.
</pre>
<blockquote type="cite" style="color: rgb(0, 0, 0);">
<pre wrap=""><span class="moz-txt-citetags">> </span>What I do know is that when the 32bit elevation model is viewed through
<span class="moz-txt-citetags">> </span>ArcGIS, its default setting was on "standard deviation stretch". If I change
<span class="moz-txt-citetags">> </span>it to "none", it gives the correct elevation values. However, this seems to
<span class="moz-txt-citetags">> </span>only be a display setting;
</pre>
</blockquote>
<pre wrap="">You are correct - this is a display setting in ArcGIS and does not
reflect some fundamental nature of the file.
> when I converted the 32 to 8bit using
</pre>
<blockquote type="cite" style="color: rgb(0, 0, 0);">
<pre wrap=""><span class="moz-txt-citetags">> </span>gdal_translate (which is the same as your example), the resulting 8bit image
<span class="moz-txt-citetags">> </span>did not have any stretching when I viewed it in ArcGIS. However,the
<span class="moz-txt-citetags">> </span>conversion did produce my8bit.tif along with my8bit.aux.xml.
<span class="moz-txt-citetags">> </span>
<span class="moz-txt-citetags">> </span>Normally, when i open images in photoshop, i only plan to loose the
<span class="moz-txt-citetags">> </span>georeferencing information, however, it seems that when i open my8bit.tif, i
<span class="moz-txt-citetags">> </span>also loose the proper colors. I think this is because the color information
<span class="moz-txt-citetags">> </span>is stored in the .aux.xml file, but I dont know how to produce a .tif that
<span class="moz-txt-citetags">> </span>is any different (that does not have a .aux.xml file)
</pre>
</blockquote>
<pre wrap="">What colors do you see? Just a range of greys? Once again, you speak
of "proper colors", but I will claim there is no inherent colors involved.
Perhaps you just mean it is using a stretch or display mode that does not
meet your expectations or wishes.
</pre>
<blockquote type="cite" style="color: rgb(0, 0, 0);">
<blockquote type="cite" style="color: rgb(0, 0, 0);">
<pre wrap=""><span class="moz-txt-citetags">>> </span>Note that raw DEM data has no inherent coloring so it doesn't really mean
<span class="moz-txt-citetags">>> </span>anything to say "so that the actual .tif grayscale colors are not
<span class="moz-txt-citetags">>> </span>stretched
<span class="moz-txt-citetags">>> </span>at all" in this context.
</pre>
</blockquote>
<pre wrap=""><span class="moz-txt-citetags">> </span>
<span class="moz-txt-citetags">> </span>I tryed converting my 8bit.tif to 8bit.raw,
</pre>
</blockquote>
<pre wrap="">Two issues. First, when I said raw I wasn't so much speaking of a file
format, but rather of "dem data as typically provided by data providers
before being processed into special visualization form, like a shaded
relief". Second, gdal_translate does <b class="moz-txt-star"><span
class="moz-txt-tag">*</span>not<span class="moz-txt-tag">*</span></b> decide on file format based
on file extensions, so you just produced a TIFF that happened to have
the extension .raw.
> then back to an 8 bit.tif, but i
</pre>
<blockquote type="cite" style="color: rgb(0, 0, 0);">
<pre wrap=""><span class="moz-txt-citetags">> </span>still always end up with a .aux.xml file even with the .raw route. In other
<span class="moz-txt-citetags">> </span>words, any method I try, I always end up with an image that is correctly
<span class="moz-txt-citetags">> </span>seen my GIS programs, but incorrectly seen by photoshop. I need the correct
<span class="moz-txt-citetags">> </span>grayscale in photoshop so that I can interactively make new RGB color
<span class="moz-txt-citetags">> </span>gradients that use the elevation informaiton. I am definitely missing a
<span class="moz-txt-citetags">> </span>concept somewhere along the way... The way I see it, its the .aux.xml file
<span class="moz-txt-citetags">> </span>about color that I want embedded into the .tif instead. Is this what is
<span class="moz-txt-citetags">> </span>meant by "applying a color table"?
</pre>
</blockquote>
<pre wrap="">I don't know what photoshop does, and you haven't given any details on the
nature of the file (such as a gdalinfo or tiffinfo report). I am really
not sure I can help you since the issues seem mostly to be "how do I get
photoshop to display things the way I hope it will", and this isn't a
photoshop mailing list.
Best regards,
<div class="moz-txt-sig">--
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up | Frank Warmerdam, <a
moz-do-not-send="true" class="moz-txt-link-abbreviated"
href="mailto:warmerdam@pobox.com">warmerdam@pobox.com</a>
light and sound - activate the windows | <a moz-do-not-send="true"
class="moz-txt-link-freetext" href="http://pobox.com/%7Ewarmerdam">http://pobox.com/~warmerdam</a>
and watch the world go round - Rush | Geospatial Programmer for Rent
</div></pre>
</blockquote>
<br>
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