GIMP: Automatically blur/fade/mask edges of multiple layers - gimp

Question

I have many layers with irregular boundaries, and a background. I would like to "blend in" the images to the background by applying some sort of filter on their boundaries, gradually. Is there a way of doing this automatically?
What I tried is:
Merge all layers
Select the background of this combined layer
Invert selection
Apply feather to the selection
Fill in the selection with white colour in the mask layer
This method sort of works, but my problem is I have overlapping layers. This means the method above fades the boundaries of the layers to the background but not to each other.
I never tried scripting in GIMP, but I'm more than willing to try it, if anyone has a working solution.

Answer 1

Yes - that can be scriptable.
Basically, scripting in GIMP can perform any action usually possible through the UI, and some that aren't.
So, once you identify the steps you need to perform for each desired layer -
like, selecting by color with maximum threshold and disalowing transparency - (that should give you a selection with the shape of the layers' visible contents).
Then, shrinking, inverting and feathering the selection
and applying "gimp edit cut", or, programatically "gimp-edit-fill", with "TRASPARENT_FILL".
For each of these actions, you can check the avaliable calls under help->procedure_browser.
Now, to create a GIMP Python script, what you have to do is:
create a Python 2 program that will import everything from the "gimpfu" module; place it as an exectuable in a GIMPs plug-in folder (check the folders atedit->preferences->folders`
In the script, you write your main function and any others - the main function may take as input parameters any GIMP object, like Image, Drawable, color, palette, r simply string and integer you want -
And after that you place an appropriate call to the register gimpfu.register function - that will enable your script as a plug-in, with its own menu option in GIMP. Finish the script by placing a call to gimpfu.main().
Also, there are no "ready" ways for one to select a set of layers in a plug-in,rather than having just the currently active layer as input. As a very convenient workaround for these cases, I abuse the "linked" layer marker (clicking on the layer's dialog, to the imediate right of the visibility icon will display a "chain" icon indicating a layer is linked)
All in all, the template for your plug-in is just:
#! /usr/bin/env python
# coding: utf-8
import gimp
from gimpfu import *
def recurse_blend(img, root, amount):
if hasattr(root, "layers"):
# is image or layer group
for layer in root.layers:
recurse_blend(img, layer, amount)
return
layer = root
if not layer.linked:
return # Ignore layers not marked as "linked" in the UI.
# Perform the actual actions:
pdb.gimp_image_select_color(img, CHANNEL_OP_REPLACE, layer, (0,0,0))
pdb.gimp_selection_shrink(img, amount)
pdb.gimp_selection_invert(img)
pdb.gimp_selection_feather(img, amount * 2)
pdb.gimp_edit_clear(layer)
def blend_layers(img, drawable, amount):
# Ignore drawable (active layer or channel on GIMP)
# and loop recursively through all layers
pdb.gimp_image_undo_group_start(img)
pdb.gimp_context_push()
try:
# Change the selection-by-color options
pdb.gimp_context_set_sample_threshold(1)
pdb.gimp_context_set_sample_transparent(False)
pdb.gimp_context_set_sample_criterion(SELECT_CRITERION_COMPOSITE)
recurse_blend(img, img, amount)
finally:
# Try to restore image's undo state, even in the case
# of a failure in the Python statements.
pdb.gimp_context_pop() # restores context
pdb.gimp_selection_none(img)
pdb.gimp_image_undo_group_end(img)
register(
"image_blend_linked_layers_edges", # internal procedure name
"Blends selected layers edges", # Name being displayed on the UI
"Blend the edges of each layer to the background",
"João S. O. Bueno", # author
"João S. O. Bueno", # copyright holder
"2018", # copyright year(s)
"Belnd layers edges", # Text for menu options
"*", # available for all types of images
[
(PF_IMAGE, "image", "Input image", None), # Takes active image as input
(PF_DRAWABLE, "drawable", "Input drawable", None), # takes active layer as input
(PF_INT, "Amount", "amount to smooth at layers edges", 5), # prompts user for integer value (default 5)
],
[], # no output values
blend_layers, # main function, that works as entry points
menu="<Image>/Filters/Layers", # Plug-in domain (<Image>) followed by Menu position.
)
main()