Thanks Chaitanya,<br><br>i forgot to add, that I was refering to an option in gdalbuildvrt, there is no way of specifying expansion there ?<br>(otherwise, there is a lot of manual work to do in the XML)<br><br>Let me know if I am wrong !<br>
<br>I solved my problem by<br> 1) Creating a VRT on the original RGB tiles<br> 2) Creating a 20% size "sample.tif" RGB tiff from the VRT<br> 3) running rgp2pct on sample.tif<br> 4) running a new rgb2pct on all the tiles, using the result from 3) as -pct option<br>
<br>That way I get the same colour table on all tiles, and it looks acceptable.<br><br><br>- oyvind<br><br><br><div class="gmail_quote">On Wed, Apr 11, 2012 at 10:55 AM, Chaitanya kumar CH <span dir="ltr"><<a href="mailto:chaitanya.ch@gmail.com">chaitanya.ch@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Oyvind,<br><br>VRT does support colortable expansion.<br>Check out the ComplexSource sub-topic in the vrt doc page[1]. <blockquote style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex" class="gmail_quote">
>From the The ComplexSource supports fetching a color component from a source
raster band that has a color table. The ColorTableComponent value is the
index of the color component to extract : 1 for the red band, 2 for the
green band, 3 for the blue band or 4 for the alpha band.<br></blockquote><br>[1]: <a href="http://www.gdal.org/gdal_vrttut.html" target="_blank">http://www.gdal.org/gdal_vrttut.html</a><br><br><div class="gmail_quote"><div>
<div class="h5">On Wed, Apr 11, 2012 at 1:27 PM, Oyvind Idland <span dir="ltr"><<a href="mailto:oyvind.idland@gmail.com" target="_blank">oyvind.idland@gmail.com</a>></span> wrote:<br>
</div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div class="h5">Hello,<br><br>I am fiddling with some old scanned (handmade) maps. In order to reduce the size of the data, and since<br>
the maps has a limited amount of colors, i figured that using palettized 8BPP tiffs would be suitable in this <br>
case.<br><br>I got several tiles that make up the whole area, using rgb(0,0,0) as nodata (making JPEG compression<br>unsuitable)<br><br>The idea was to use VRT to join these together, but since they all have different color tables,<br>
this is not possible.<br><br>Would it be an idea to implement support for an "expand option" in VRT, e.g expanding to rgb/rgba ?<br><br>Not sure how many would need this feature though.<span><font color="#888888"><br>
<br><br>-- oyvind<br>
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<br clear="all"><br>-- <br>Best regards,<br>Chaitanya kumar CH.<br>
<br><a href="tel:%2B91-9494447584" value="+919494447584" target="_blank">+91-9494447584</a><br>17.2416N 80.1426E<br>
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