[GRASS-user] color anomalies after orthorectification

[Markus Metz]

On Fri, Feb 21, 2014 at 9:27 AM, . . <st_kiefer at web.de> wrote:
> Hi Markus,
> thanks for that hint, that might be the solution. As I must confess I did
> not only try any of the other methods, believing cubic would yield the best
> results because the scans are from an area with high energy of relief.

I would leave it as it is. Bicubic gives nice results, but these
overshoots must be taken care of. Your method of forcing values back
to the range of 1,254 seems appropriate to me for handling resampling
overshoots.

Markus M


> I will try this when I'm back in office and give a feedback of my
> experiences then.
>
> best regards
>
> Stefan
>
>> Markus Metz <markus.metz.giswork at gmail.com> hat am 21. Februar 2014 um
>> 08:05 geschrieben:
>>
>>
>> On Fri, Feb 21, 2014 at 12:26 AM, Stefan Kiefer <st_kiefer at web.de> wrote:
>> > Hi,
>> > I tried to orthorectify aerial photographs. That worked fine by now,
>> > until
>> > i got scans wich appear to be darker as before. At least this is the
>> > first
>> > observation I made. The effect occured with that scans is, that after
>> > rectification some of the dark areas become white (or rather null,
>> > querying
>> > that cells result in -0.722622310236638).
>>
>> This should only happen with method=cubic or method=cubic_f. The other
>> resampling methods nearest,bilinear,bilinear_f should not produce
>> these resampling overshoots.
>>
>> Markus M
>>
>>
>> > Has anyone had similar experiences when rectifying aerial photographs.
>> > And
>> > hopefully a hint how to avoid this damages. I suspect that the
>> > orthorectified images become double precision whereas the imported scans
>> > are
>> > integer...
>> >
>> > best regards
>> >
>> > Stefan
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