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<div class="moz-cite-prefix">Hi Jonathan,<br>
<br>
Is it possible that QGIS is using the infrared band as an alpha
channel? This might explain the whitening effect, especially in
non-vegetated areas. I would check the Layer properties
Transparency tab to see whether anything is set as the
transparency band. If it is, you could override QGIS by setting a
default style.<br>
<br>
Cheers,<br>
<br>
Andy<br>
<br>
On 02/12/2013 11:53, Jonathan Moules wrote:<br>
</div>
<blockquote
cite="mid:CAA-xNcWfLo690+cRA-zo5Ki+z4tE9mSMcrNzrVpOfhQJ+55PZg@mail.gmail.com"
type="cite">
<meta http-equiv="Content-Type" content="text/html;
charset=ISO-8859-1">
<div dir="ltr">Hi List,
<div>I've got a 4 band raster aerial photography (RGBI) that
comprises lots of tiles. I've merged some of the tiles
together with:</div>
<div><br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">gdal_merge
-o 1.tif -of GTiff -co TILED=YES -co BIGTIFF=YES -co
COMPRESS=JPEG -co JPEG_QUALITY=50 -co BLOCKXSIZE=512 -co
BLOCKYSIZE=512 --optfile tiff_list.txt</blockquote>
<div><br>
</div>
<div>But the resultant file looks funny in QGIS.</div>
<div>This is what the source file looks like (correct):</div>
<div><img src="cid:part1.04060602.00010309@geodata.soton.ac.uk"
alt="Inline images 1"><br>
</div>
<div><br>
</div>
<div>This is what the merged file looks like (wrong):</div>
<div><img src="cid:part2.00000803.08000704@geodata.soton.ac.uk"
alt="Inline images 2"><br>
</div>
<div><br>
</div>
<div>All the shadows are a whitey colour. This doesn't happen
with 3-band (RGB) images.</div>
<div>I've tried comparing individual bands; they all look
different in the 4-band.</div>
<div><br>
</div>
<div>However, if I open the four-band in ArcGIS, it looks fine
(both source and original).</div>
<div><br>
</div>
<div>Anyone know what's going on? Is it a QGIS bug or is it
doing something "smart"; I can't see anything odd going on
with symbology.<br>
</div>
<div><br>
</div>
<div>Thanks,</div>
<div>Jonathan</div>
</div>
<br>
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<br>
<br>
<pre class="moz-signature" cols="72">--
Andy Harfoot
GeoData Institute
University of Southampton
Southampton
SO17 1BJ
Tel: +44 (0)23 8059 2719
Fax: +44 (0)23 8059 2849
<a class="moz-txt-link-abbreviated" href="http://www.geodata.soton.ac.uk">www.geodata.soton.ac.uk</a>
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