Re: [Openev-discuss] Different colors ECW / GEOTIFF

[Frank W. <fwa...@gm...>]

On 6/9/05, Fr=E9d=E9ric Trastour <de...@sp...> wrote:
> Hello,
>=20
> when i load in OpenEV the same image ( Landat GEOCOVER ) in ECW or in Geo=
Tiff
> i have do not the same result : colors are very different between the two=
 files.
>=20
> I have attached a screenshot, tiff is on the left, ecw on the right.
>=20
> Note that OpenEV is the only software which give these colors with the EC=
W file.
> If i display
> this image in ERviewer for example, i get the same colors than OpenEV wit=
h the
> GeoTiff.
>=20
> The ECW is obtained via :
>     gdal_translate IM.TIF IM.ECW -of ECW -co "TARGET=3D70"
>=20
> Does OpenEV apply some particular processing on ECW images ?
>=20
> On this particular dataset, I prefer the aspect of the ECW in OpeneEV and=
 would
> like to
> apply the same processing outside OpenEV.

Fr=E9d=E9ric,

I'm afraid I don't know why you are seeing this difference.   My first
assumption was that it was a scaling difference, but OpenEV should not
apply any scaling for 8bit imagery by default.=20

My next guess was that it somehow relates to how the overviews
are generated.  By default files without overviews will have their
OpenEV overview representations computed based on decimation,
though this may be changed on the "Raster" tab of the preferences=20
dialog to Average.  But when loading from .ecw files, I think OpenEV
is essentially using the ECW provided overviews which are effectively
generated by reduced expansions of the wavelet equations (as I understand
it) which might give more of an averaged effected rather than decimation.

Well, that might explain it, but I don't know why you wouldn't see the
same differene in the ERviewer. =20

I tried to replicate your situation with an image I had lying around,
but saw no discernable difference. =20

Can you point me to the raw image in question so that I could experiment
with it a bit?

Best regards,
---------------------------------------+-----------------------------------=
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam@pobox.c=
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and watch the world go round - Rush    | Geospatial Programmer for Rent