Chris Emberson wrote:
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
Upsample fileB.tif here:
gdalwarp -r bilinear -ts newwidth newheight fileB.tif fileB2.tif
Where newwidth and newheight are a few times larger than original.
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
> >> >
> >> > _________________________________________________________________
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> >>
> >>
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>
>
> --
> Best regards,
> Chaitanya kumar CH.
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