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The rasters do have colour tables applied, that are expressed using RGB values, using gdaldem:<br>75% 107 0 0<br>50% 196 109 27<br>25% 247 195 72<br>0% 252 233 109<br>nv 0 0 0 0<br><br>They are not derived from vector data however. I am unsure of your requirement in terms of the source of the raster data. All of the pixel values have been created and either fall between the values of 1-4 or contain no data.<br><br>The commands I am running on the files are:<br>gdal_translate -of GTiff -co "TILED=YES" -b 1 -b 1 -b 1 fileA.asc fileB.tif<br>gdaldem color-relief fileB.tif rgb.txt fileC.tif -alpha<br>gdalwarp -s_srs EPSG:27700 -t_srs EPSG:900913 -r bilinear fileC.tif fileD.tif<br><br>an example of how the bilinear is working (fileD.tif) can be seen in the attached file. I have tried running running the gdalwarp command above prior to gdaldem but this makes little difference.<br><br>TIA,<br>Chris<br><br><br><br>> Date: Mon, 5 Oct 2009 16:46:55 +0530<br>> Subject: Re: [gdal-dev] Anti-Aliasing<br>> From: chaitanya.ch@gmail.com<br>> To: chrisemberson@hotmail.com<br>> CC: seth@pricepages.org; gdal-dev@lists.osgeo.org<br>> <br>> Chris,<br>> <br>> The images look like they have a colour table instead of RGB bands.<br>> Also, they seem to be converted from vector to raster. Correct me if I<br>> am wrong.<br>> <br>> Anti aliasing images with colour tables is a little more involved and<br>> depends on the type of result required. Can you provide the source for<br>> these images?<br>> <br>> One method would be to convert the image into RGB, apply bilinear or<br>> any other interpolation method, and convert it back to the colour<br>> table from RGB. If the source is a vector, we can smooth the shapes by<br>> using curves in place of straight lines.<br>> <br>> On Mon, Oct 5, 2009 at 3:59 PM, Chris Emberson<br>> <chrisemberson@hotmail.com> wrote:<br>> > Seth,<br>> ><br>> > Thanks for the reply. The attached image hopefully will clarify the problem<br>> > I am having. On the left of the image is the output I would like (I have<br>> > produced this using a GIS). On the right is the output using mapnik and<br>> > gdal. The problem is the pixellated effect between the raster values on the<br>> > RHS.<br>> ><br>> > The GIS isn't that great as far as batch processing is concerned, hence why<br>> > I am trying to use the GDAL utilities that ship with mapnik. The option in<br>> > the GIS that produces the desired effect is "anti-aliasing (bilinear<br>> > interpolation)", but it appears as though there is a more sophisticated<br>> > smoothing algorithm being employed? I have tried running the various<br>> > interpolation techniques with gdalwarp but none of them produce a crisp<br>> > output. I have tried also increasing the resolution of the raster by 5x<br>> > (both width and height) using "gdal_translate" and "-outsize 500% 500%"<br>> > this doesn't help either.<br>> ><br>> > Any suggestions gratefully received,<br>> ><br>> > Chris<br>> ><br>> ><br>> ><br>> ><br>> >> Date: Fri, 2 Oct 2009 12:36:24 -0500<br>> >> Subject: Re: [gdal-dev] Anti-Aliasing<br>> >> From: seth@pricepages.org<br>> >> To: chrisemberson@hotmail.com<br>> >> CC: gdal-dev@lists.osgeo.org<br>> >><br>> >> Could you give an example of the problem? Anti-aliasing generally only<br>> >> applies when you are going from vector line drawings to rasterized images.<br>> >><br>> >> If I was trying to smooth things I would first look at cubic or bilinear.<br>> >> Any other resampling may enhance any noise in your image.<br>> >> ~Seth<br>> >><br>> >> On Fri, October 2, 2009 11:16 am, Chris Emberson wrote:<br>> >> ><br>> >> > I am looking for an anti-aliasing function to smooth out the pixellated<br>> >> > effect between raster values. I have tried the various interpolation<br>> >> > methods with gdalwarp and have also increased the resolution of the<br>> >> > raster<br>> >> > to try and minimise the effect, to no avail.<br>> >> > Is this a function to be added soon?<br>> >> ><br>> >> > Thanks,<br>> >> > Chris<br>> >> ><br>> >> > _________________________________________________________________<br>> >> > Share your photos with Windows Live Photos – Free.<br>> >> ><br>> >> > http://clk.atdmt.com/UKM/go/134665338/direct/01/_______________________________________________<br>> >> > gdal-dev mailing list<br>> >> > gdal-dev@lists.osgeo.org<br>> >> > http://lists.osgeo.org/mailman/listinfo/gdal-dev<br>> >><br>> >><br>> ><br>> > ________________________________<br>> > New! Receive and respond to mail from other email accounts from within<br>> > Hotmail Find out how.<br>> > _______________________________________________<br>> > gdal-dev mailing list<br>> > gdal-dev@lists.osgeo.org<br>> > http://lists.osgeo.org/mailman/listinfo/gdal-dev<br>> ><br>> <br>> <br>> <br>> -- <br>> Best regards,<br>> Chaitanya kumar CH.<br> <br /><hr />Add other email accounts to Hotmail in 3 easy steps. <a href='http://clk.atdmt.com/UKM/go/167688463/direct/01/' target='_new'>Find out how.</a></body>
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