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<p class="MsoNormal"><span style="color:#1F497D">Hi Johannes,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Thanks for getting back to me. In general we would use the same value for each band, so 256 or -9999. We only work, where possible with GeoTIFF, so the Internal Mask idea is a nice one I hadn’t thought of. Also
the use of an ALPHA channel, might be an option. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">I could be wrong, but in relation to the internal masking, I believe it can be difficult for some CAD and GI Software to recognise internal masking, I believe there’s even an issue with GeoServer, which we use
extensively here. As you say an Alpha Band is also an option…I will need to experiment a little more!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Once again, thank you for your response!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Richard.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
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——</span><br>
<span style="FONT-FAMILY: Arial, sans-serif; FONT-WEIGHT: bold; COLOR: #004d44">Richard McDonnell MSc GIS, FME Certified Professional</span><br>
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<p class="MsoNormal"><b><span lang="EN-US" style="mso-fareast-language:EN-IE">From:</span></b><span lang="EN-US" style="mso-fareast-language:EN-IE"> Johannes Kröger (WhereGroup) <johannes.kroeger@wheregroup.com>
<br>
<b>Sent:</b> 14 January 2022 09:39<br>
<b>To:</b> Richard McDonnell <richard.mcdonnell@opw.ie>; Qgis Users List <qgis-user@lists.osgeo.org><br>
<b>Subject:</b> Re: [Qgis-user] NoData in RGB Imagery<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p>Hey Richard,<span style="font-size:12.0pt;mso-fareast-language:EN-IE"><o:p></o:p></span></p>
<p>do you have different NODATA pixels between the three bands (R, G, B) or is it the same? If there are no differences then you can use an additional channel as mask. I would suggest you store your imagery in GeoTIFF with an "internal mask". Even posted a
nice example of this in <a href="https://lists.osgeo.org/pipermail/gdal-dev/2014-August/039907.html">
https://lists.osgeo.org/pipermail/gdal-dev/2014-August/039907.html</a><br>
If your format supports RGBA (e.g. PNG), then that would be another way to achieve this but a nice GeoTIFF should be the best solution.<o:p></o:p></p>
<p><br>
Cheers, Hannes<o:p></o:p></p>
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<p class="MsoNormal">Am 13.01.22 um 18:35 schrieb Richard McDonnell:<o:p></o:p></p>
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<p class="MsoNormal">Hi all,<o:p></o:p></p>
<p class="MsoNormal">I have a general GIS query and am hoping I can get some insight from the community.<o:p></o:p></p>
<p class="MsoNormal">It relates to how we deal with pixels with no data in RGB Imagery. It seems to be typical to produce RGB imagery as 8bit with pixel values between 0 and 255, with either 0 or 255 being used as the NoDATA value. To me this is problematic,
as there can be valid pixels within your image with 0 or 255. To me the solution is to use 16bit Imagery and to assign the NoDATA value to any value outside of the 0 – 255 range.<o:p></o:p></p>
<p class="MsoNormal">I know in DEM’s its usual to use -9999 as your NoDATA value but my question is, Is there a standardised way to deal with NoDATA in RGB?<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">I welcome any comments and suggestions.<o:p></o:p></p>
<p class="MsoNormal">Regards & Thanks in advance,<o:p></o:p></p>
<p class="MsoNormal"><br>
Richard.<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal" style="line-height:11.25pt"><b><span style="font-size:9.0pt;font-family:"Arial",sans-serif;color:#004D44;mso-fareast-language:EN-IE"><br>
——</span></b><span style="font-size:9.0pt;font-family:"Arial",sans-serif;color:#004D44;mso-fareast-language:EN-IE"><br>
<b>Richard McDonnell MSc GIS, FME Certified Professional</b><br>
<i>FRM Data Management</i><br>
<br>
——<br>
<b>Oifig na nOibreacha Poiblí</b><br>
Office of Public Works<br>
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</span><b><span style="font-size:9.0pt;font-family:"Arial",sans-serif;color:#565148;mso-fareast-language:EN-IE">Sráid Jonathan Swift, Baile Átha Troim, Co na Mí, C15 NX36
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