[gdal-dev] gdaladdo and cubic resampling

[Chaitanya kumar CH]

Armin,

GDAL's resampling algorithms for overviews are a bit restricted. Your best
bet is to smoothen the image with an image processing software.

On Thu, Aug 5, 2010 at 11:00 PM, Armin Burger <armin.burger at gmx.net> wrote:

> Chaitanya
>
> I send the image just to you since it's not small any more. This is a
> mosaic of 3 versions of GDAL overviews:
>
> left: nearest
> middle: cubic
> right: gauss
>
> as you can see, nearest and cubic are looking very similar, quite grainy
> (which I would expect from nearest but not from cubic convolution). The
> gaussian on the other hand is very much smoothed, already a bit blurred. I
> was expecting that cubic would produce much less grainy results than nearest
> but less blurred effects than gaussian.
>
> Regards
> Armin
>
>
> On 05/08/2010 14:52, Chaitanya kumar CH wrote:
>
>> Armin,
>>
>> Can you provide a sample image that shows this problem?
>>
>> On Thu, Aug 5, 2010 at 5:57 PM, Armin Burger <armin.burger at gmx.net
>> <mailto:armin.burger at gmx.net>> wrote:
>>
>>    Hi all
>>
>>    I have a question regarding the resampling modes for the gdaladdo
>>    utility. Since the overviews are used by Mapserver afterwards, I ran
>>    some tests with a map file referencing the Tiff image and the
>>    shp2img tool to output the results.
>>
>>    I found the gauss resampling smoothening the image a bit too much.
>>    Therefore I wanted to try the "cubic" resample method using the GDAL
>>    version included in FWTools 2.4.7 (1.7.0b2), but to me it looks like
>>    that this does not have any effect compared to "nearest" resampling.
>>    Does anybody have a clue why? Command used was
>>
>>    gdaladdo -ro  -r cubic  image.tif 2 4 8 16 32 64
>>
>>    Thanks in advance for any help
>>    Armin
>>
>>
>>
>>    --
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>>
>>
>>
>>


-- 
Best regards,
Chaitanya kumar CH.
/tʃaɪθənjə/ /kʊmɑr/
+91-9494447584
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