[Gimp-user] select shadows

[David Gowers]

Hi norman,

On Tue, Apr 7, 2009 at 12:15 AM, norman <norman at littletank.org> wrote:
> I know how to select by colour but is it possible to select by tonality
> such as shadow area. Please help an ignorant Gimper.

Of course; for applications like this, I typically use QuickMask mode.

I
1. Copy the image
2. Enter QuickMask mode
3. Paste the image and Anchor it
4. Colors->Auto->Normalize
5. Exit QuickMask mode

The above will select pixels based on their intensity -- a pixel of 0
intensity being 0% selected, 127 intensity == 50% selected, 255 ==
100% selected.
You could modify this with various tools in the Colors menu to get the
desired effect.
For instance, your original 'select the shadows' idea could be done by simply
1. Colors->Invert
2. Adjust with Colors->Curves to taste, or threshold using
Colors->Threshold if you wanted a hard-edged selection

The above is the advanced method, with more control and
sophistication. However, simply setting the 'select by' option to
'Value' for the 'select by color' tool might do what you want.

Hope that helps!

David