[Gimp-developer] what algorithm is used in Ctrl-K?

[saulgoode at flashingtwelve.brickfilms.com]

Quoting zhang chi <zhangchipr at gmail.com>:

> http://www.gimptalk.com/forum/topic/My-First-Tutorial-Blending-Images-In-Gimp-106-1.html<gimp-developer@lists.XCF.Berkeley.EDU>
>
> in this tut, after feather,C-i,and C-K is used, but what algorithm is used
> when using Ctrl-k ?
>
> thank you <gimp-developer at lists.XCF.Berkeley.EDU>


If the layer has an alpha channel then the value of the alpha is  
scaled by (1 - S) where "S" is the selection mask's value (which spans  
the range '0=not selected' to '1=fully selected' -- the selection is  
actually a value from 0 to 255).

If there is no alpha channel then the value of each of the components  
(RGB) is scaled by (1 - S) and added to the product of the  
corresponding component of the active background color and (1 - S).

For Indexed Mode images, the resulting pixel is the active BG color if  
S>0.5 and unchanged if S<0.5