[Gimp-user] Can't recompose LAB: Specified layer # not found

[saulgoode at flashingtwelve.brickfilms.com]

Quoting Colin Brace <cb at lim.nl>:
   :
   :
> 5)Duplicate B layer, set "B Copy" to overlay (Opacity is 100%).
> 6)Merge both B layers (Image>Merge Visible Layers/CTRL-M) Choose Expand as
> necessary (though other options don't make a difference in this case) Hit
> Ok.
> 7)Repeat steps #4 through #6 for the "A" layer.
>
> However, after following these steps, when I click the "Recompose" command,
> I get an error message on the status line:
>
> Specified layer [some number] not found.

The problem is that 'Recompose' relies upon the layer IDs of the three  
layers and your merging of two layers results in the new layer being  
given a different layer ID.

As a work-around, you need to duplicate your B layer twice and work  
with the two copies, leaving the original layer untouched. After you  
have completed your editing and merged your copies together, perform  
an "Edit->Cut", Paste it onto the original layer, and Anchor the  
floating layer.

Unlike Merging, pasting and anchoring will not change the layer ID of  
the original layer and Recompose will function as expected.