On 11-10-29 12:18 PM, Komяpa wrote:
Still, there are some things I would like to clear / discuss.
1) gdaladdo final.tif 2 4 8 16 32 64 128 256 makes not beautiful
overviews. If I add -r average, some artifacts start appearing, like
the vertical stripes on the link above. Any good ways to fix that?
Darafei
I would be interested in reproducing this at my end and investigating.
Could you provide something I can work with? I presume the issue
relates to the average overview builder not understanding nodata
masking. Are you using GDAL "trunk"?
3) JPEG compression artifacts.
Black field outside makes outmost blocks appear darker and be "dirty":
http://latlon.org/maxi?zoom=18&lat=56.32465&lon=30.61984&layers=0000000000000FF0000FBT
This can be avoided, as far as I can see, in two ways:
a) easier one, on compression, if we fill NODATA region inside these
blocks not with black, but with bilinear average of other data inside
block, there will be no black blocks.
b) harder one, make custom jpeg decompressor that will take exact
value for nodata region into account and try to restore values for
DATA region (not sure if it's really possible).
Same about compressing overviews. Probably nearblack can be patched to
fill regions not with black but with any kind of average, as
quick-and-dirty solution?
I don't see this as the role of nearblack, but I can see it might
be helpful to have a way of doing this to an image under the nodata
mask as a distinct utility. Alternatively since this is mostly an
issue with the jpeg compressor, perhaps just to do it within the
geotiff through jpeg writing code in GDAL.
Can you provide something that helps me isolate this problem to
work on?
Best regards,
--
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