GIMP Version:
Operating System: Windows
GIMP Experience: New User

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OK so I'll start off by saying I have next to ZERO experience in using graphic design/photo editing software. I plan to eventually familiarize myself with all the essential GIMP techniques, but for now I need help (or at least the name of the technique used so I can search for a tutorial) with isolating an object in an image and then changing the space occupied to a different image.

For example, how would I go about changing the outer space scene in this image?

I removed the white background from the image, locked the transparency on the resulting layer and filled it with black. This image has a transparent background.

You may want to try RobA's Transparent Background script. It removes most of the white and there are a few places that need to be touched up afterward before locking the transparency and filling it with black.
http://gimpscripts.com/?s=transparent+background

1. Open your image in Gimp.
2. Using the Color by Selection tool, choose the white background.
3. Select menu | Save to Channel.
4. In a new layer add a different background.
5. With the new layer active & if initial selection is still available, Edit menu | Clear (delete).
5a. or if no selection available, Channels dialog | Channel to Selection, Edit menu | Clear (delete).

How do you "lock the transparency"? I played around with the "Select by Color" tool, and was able to remove the white background leaving just the alpha layer (although it also left a few small holes in the outer space scene) but after that I didn't know how to select the remaining image in order to change its color.

Up on the right hand corner where you see you layers, paths, etc, just below it is where you lock the transparency, just click it.

Check this trick for getting rid of errant pixels, Subject: Surround Selection Trick
This might help too, Subject: How do I remove the background from an image?

This community is amazing, thanks alot guys

Was messing around with adding a different background using Odinbc's instructions, and the results seem much less 'crisp' than the original.



Original for reference:


I figured this could be a byproduct of using the "Select by Color" tool, but Oregonian's work doesn't seem to have this problem. What did I do wrong? (Also the lines between the feathers and the fade effect on the tips are gone but I don't expect to be able to duplicate that)

As you have noticed. There are a number of ways this can be accomplished.
This method I use seems to work pretty good for me.

This silhouette image below is what I ended up with.


Working on a duplicate of the image. I first desaturated choosing Luminosity.



I then used Curves, using the setting seen in the Curves dialog below.



Next I used Levels, to remove more of the lighter grays and whites.
The Levels dialog below shows the settings I used.



After coloring the remaining white/gray that was left over with black. I did a Color to Alpha on the image using white as the color to be removed from the Alpha Channel.



Note: The coloring stage can be used to further refine the silhouette image as you see fit.

I can tell you how I would go about doing it after loading to GIMP and creating a hidden duplicate of the original.

1) Choose "Fuzzy Select" for the selection type.
2) Click the white outside of the figure.
3) Select "Invert" from the "Select" menu.
4) Click delete to empty the space scene.
5) Create a new layer.
6) Use one of the excellent space tutorials to create your own space scene . Note: I did this quickly so didn't use a tutorial. I did use Gimper66's excellent star brush. viewtopic.php?f=23&t=12389
7) Export and enjoy.


Edited to add: I missed a few of the white spots. What you can do then between steps 2 and 3 is switch to "Add to current selection" in the "Fuzzy Select" tool options and click the internal white spaces you want to keep separately (around the hair, and the arm and legs). Only then do the invert and delete.

my result using Luce filter