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Separating photo elements
    Hi Gimps…
Been using Gimp for a couple of years and have a basic understanding of using Layer Masks. I’ve got a photo (see attachment), of a plane. I need to change the color of the plane, no problem. But I also need to tone down the orange in the background sky. Simply, I need to separate the plane from the sky so I can work on each separately and then merge the images.
I could probably come up with a way to do this but, as usual for me, I’d “over engineer” the process. A simple solution would be much appreciated.
Thanks in advance,
(07-01-2019, 07:57 PM)bcripps Wrote: Simply, I need to separate the plane from the sky so I can work on each separately and then merge the images.

As usual, more than one way.

Using Layer Masks
1. Duplicate the layer
2. Hide the lower layer by using the eye in the Layers dialogue
3. Add a Layer Mask to the top layer, default white.
4. Make the background of the top layer transparent by painting with black on the Layer Mask
5. Use eye to make lower layer visible again.
6. Adjust colours of each layer as required
7. No need to merge, Save as xcf keeping the layers intact.

Using Paths
1. Use the Path Tool to trace the outline of the plane
2. In the Paths dialogue, use the Path to Selection icon to create a selection on the plane
3. Copy the selection; Paste as a new layer above the original image.
You now have the 2 layers that can be adjusted separately.
Messing about on my netbook and packing in before the battery expires. All sorts of ways.

This Gimp 2.8 but 2.10 the same (or better)

[Image: RvEz7Ew.jpg]

I would use 3 copies one for sky, one for plane and the rest. Layer masks to separate. 
Layer group(s) if required.

Then it depends how you want to recolour. Example uses color-curves for the sky but a layer mode for the plane.

example attached:

Attached Files
.gz   demo.xcf.gz (Size: 948.34 KB / Downloads: 83)
Hey guys and thank you again:

Not so proficient in Layer Masks as I thought. Swapping out backgrounds I can do, but separating a single photo into layers and working on each separately has me stumped.

I’m doing something wrong, something simple probably, but my layer mask is not masking out the foreground so changes I make to the background affect both layers.

First off, I did divert from your instructions in an effort to simplify things. I made my color changes to the foreground, the plane separately, disregarding what was happening to the background, and changed the color of the plane to a rosy pink and saved that as a .png file.

My procedure after that:
  • loaded the file into Gimp as a layer and checked for Alpha Channel
  • made a duplicate of the layer
  • turned off the visibility of duplicate
  • on top layer went to Colors>Desaturate to make mask black and white
  • added Layer Mask to the top layer, default white
  • selected the active black & white thumbnail in top layer and painted out background of photo with black
  • once layer mask was completed selected Colors>Invert to make the plane mask black
  • create a Layer Mask in second layer, default white
  • copy and past black Layer Mast from the top, into the second layer
  • click anchor symbol
  • the foreground, the plane, appears as a checkerboard but, apparently, isn’t masking out the changes to the background
  • color changes to background also affect the foreground plane changing it from ‘rosy’ to washed out

Any ideas as to where I’m going wrong are much appreciated.

Included: .png file of the ‘rosy’ plane and .xcf file of the changes to the background sky with the mask in place over the plane, checkerboard.

PS: Oops. Seems the files are too big to post...
(07-14-2019, 01:43 PM)bcripps Wrote: on top layer went to Colors>Desaturate to make mask black and white
This is a mistake. The top layer is not the mask and must remain in colour.

Attached is a very simple example of your plane (done quickly and roughly). It has 2 layers and 1 layer mask.

The bottom layer is for the background. Make changes here for the sky, etc.

The top layer is for the plane. It is still in colour. In the layers dialogue, click on this (ie the colour image) to make changes to the plane.

In the layers dialogue, to the right of the top layer is the layer mask. This must be in be in gray scale. ie black, white and gray. White is opaque (the plane); black is transparent, so the bottom layer shows through; gray is semi-transparent. In the layers dialogue, click on the black and white layer mask to select it, then on the main image paint with black or white to change transparent/opaque areas.

Things you can try:

In the layers dialogue use the eye symbol to switch layers on and off to see what is in each layer.

With both layers visible, make changes to the to background layer. The plane does not change.

With both layers visible, select the top layer (the colour thumbnail) in the layers dialogue. Make changes, only the plane is affected, not the background.

In the layers dialogue, select the black and white layer mask. Right click and select "Show Layer Mask". You get a full size black and white layer mask. Click on "Show Layer Mask" again to go back to normal view.

Attached Files
.xcf   LayerMask1.xcf (Size: 790.15 KB / Downloads: 42)
Thank you, Blighty:
I need to go through these instructions again, carefully, but knowing the Desaturation was a mis-step is good to know. I thought layer masks were always B&W and that's the reason I switched from the colors.
Okay, let me play with this and I'll get back to you.
All best, and thank you...
Success, Blighty:
Thank you for your time and efforts. Following your instructions, I got the image I needed. And I didn’t even have to redo the layer mast; a little ‘copy and paste’ got me through. I’ve also saved all of your instructions for the next time.
Can’t thank you enough, really. All best…

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