[gdal-dev] Stop gdalladdo eating fillets

[Even Rouault]

Carlo A. Bertelli (Charta s.r.l.) a écrit :

Well, I think it's not really a problem, but a characteristics of the 
processing. I doubt that any general purpose pyramid building can 
preserve high frequency details like fillets. It would require special 
processing that would know what is a line and what is not, but that is 
not implemented in GDAL.

> Hallo,
> I have a set of very detailed b&w needing an overlay. But when I run
> gdaladdo, no matter what option I choose, fillets are spitefully
> deleted.
> I don't know if there is a better solution, I tried to get a thicker
> trace on a copy of the original image, make the pyramids and rename
> the resulting file.
> To make the fillets grow I used ImageMagick, like this
> convert -blur 3 -threshold 20 ORIGINAL.tif THICKER.tif
> (the treshold is less than 50 because the original image is white on black)
> gdaladdo --config COMPRESS_OVERVIEW DEFLATE -r average  --config
> INTERLEAVE_OVERVIEW PIXEL --config NODATA 0 -ro THICKER.tif 2 4 8 16
> than I renamed THICKER.tif.ovr as ORIGINAL.tif.ovr.
> Well, it doesn't work well, I should have made a thicker version while
> I was reducing the image. There is always a size where fillets
> disappear.
> The problem seems to ask for a resize method that keeps the thickness
> of the lines while reducing the objects. There should be a procedure
> like mine but carefully adapted to any scale reduction.
> Am I missing something or this is really a problem?
> Carlo
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