Separating photo elements

[Blighty]

(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.