> I have a photo of a dark red flower against a dark background.
> I've tried tedious ways to lighten the background without changing the
> but the details of the flower are too tiny. So I'm browsing tutorials.
> Should I
> be learning about masks? About layers? A hint how I can approach this?
Selection is what you need to be learning about: you need to
selecting the flower and not the background, or vice versa,
so that you can run a lightening tool (brightness-contrast, levels,
or curves) on the background without affecting the flower.
There are lots of ways of selecting: you could use paths then turn
the path into a selection, or you could use select by color or
intelligent scissors to make an approximate selection, then use the
quick mask to fine tune it and get it perfect.
For any of these techniques (maybe not siox), zoom in a lot so you
can see what you're doing and make sure you get all the fine
details. That's why these tools are better than something like
Lasso select that doesn't let you zoom in.
If you can run the development version of GIMP (2.3), the new siox
tool works quite well for flowers against a contrasting background.
A couple other tips: you'll probably want a few pixels of feathering
(but you can feather a selection after the fact, from the Select
menu), and you'll want to use View->Toggle Selection (ctrl-T) a lot
to turn off the selection boundary while you're adjusting the
brightness of the background, to make sure you don't get an obvious
looking jump at the selection boundary (if you do, try feathering more).
That should give you enough to get you started, anyway.
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