On 10/24/2012 01:44 PM, Jim Clark wrote:
> Wow--
> I will save this. Incredibly clear and detailed--I have never rally
> understood those masks. Still don't, but am sure closer!

Hey Jim,

Glad it makes sense to you!  I have saved it and I will probably do
an illustrated version for my website sometime soon.

Figuring out how to use layer masks is one of the real
"breakthroughs" that make the GIMP a powerful tool.  I have been
using the GIMP for around 10 years, but I still remember how
difficult it was for me to wrap my brain around what masks can do.

You can:

* Make templates that enable you to quickly and easily create lots
of different versions of an image, i.e. with different colorization
as in the present example, or as frames that smaller images will
appear in, etc.

* "Remove" part of a layer, spend a half hour working on the image,
then "undo" an error you just found in your removal by painting a
little white on the corresponding part of the layer's mask.  I
almost never use the "Eraser" tool - if you have to go back and undo
it, you lose all the work you did after using the Eraser.

* You can "paint with any filter" by applying filters and effects to
a copied layer, adding a black mask to make the altered layer
vanish, then painting the mask with white to make the changes come
back only where you want them in the visible image.  (Or vice versa:
 Paint black on a white mask to wipe away the filter effect where
you don't want to see it.)  I find this method especially useful
when working on portrait shots.

* Isolate under-exposed elements from over-exposed elements in
photographs, by making a layer copy and masking out the under-
exposed part of the top layer.  Then you can adjust the brightness
and colors of the bright and dark parts of the picture separately.
If the contrast between over- and under-exposed areas is strong
enough, you can use the Threshold tool on a throw-away layer to
create a nearly perfect mask in seconds, that would have taken a
LONG time to paint by hand - some call this "finding the natural mask."

* Use a black/white gradient on a layer mask to give the layer a
smooth transition from visible to invisible.  This sometimes comes
in handy when processing flash photographs, i.e. a line of people on
a stage where those at the near end are fully exposed and those at
the far end are under-exposed.

... and a whole lot more.



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