[gdal-dev] Anti-Aliasing

[Chaitanya kumar CH]

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
<chrisemberson at 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: seth at pricepages.org
>> To: chrisemberson at hotmail.com
>> CC: gdal-dev at 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.