That's a great point. So it's not a bug, it is a feature in some cases. :)
Maybe what we need is an option to switch between the two behaviors then.
On 2019-02-20 8:23 a.m., Darafei "Komяpa" Praliaskouski wrote:
I believe this behavior is great for over-compressed imagery JPEGs where
you have corrupted border of several "black-poisoned" non-black pixels
that you'd better remove and take from some other image in the mosaic,
since in this scenario you usually have an overlap.
On Wed, Feb 20, 2019 at 4:16 PM Daniel Morissette
<[email protected] <mailto:[email protected]>> wrote:
I noticed this behavior as well and I think it's a bug. I think it
would
make more sense to keep the last "-nb" pixels that are not nearblack
instead of dropping them. The effect is especially annoying when you
have image tiles and you end up with a 1-2 pixels gap between them.
I didn't test what happens if we change the behavior. So maybe there is
a reason why it was implemented this way?
Daniel
On 2019-02-19 6:13 p.m., Christopher Mitchell wrote:
> I've encountered an error in an image processing pipeline I've built
> where nearblack is removing pixels at the border of images, even if
> they don't fit the is-"black" criterion. Specifically, I'm using
> nearblack to remove nearly-black areas touching the edges of lossy
> image tiles that should be fully black. Those images are later
> combined into VRT files and warped; where we have multiple tiles
> overlapping an area, some of which are missing data, we therefore can
> get complete coverage.
>
> Unfortunately, for tiles that have no black areas, nearblack is still
> eating the -nb argument's number of pixels at the edges, turning them
> into black (0, 0, 0, 0, where we're using 4-channel images), even if
> those pixels are nowhere near the color criterion to be recognized as
> black. My understanding was that nearblack should only be proceeding
> into the interior of the non-black area and then setting pixels to
> black if those pixels are /actually/ nearly black.
>
> Am I encountering a bug with nearblack? Do I misunderstand how
the -nb
> argument works? Happy to provide a MWE if any of the above is
unclear,
> and thanks in advance.
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>
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Daniel Morissette
Mapgears Inc
T: +1 418-696-5056 #201
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Darafei Praliaskouski
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Mapgears Inc
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