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