Multiple exposure composite in GIMP

Note: as I compose this tutorial, the formatting and uploading is not working. It might take a few edits to get it right.

Preamble

I have written some informal in-thread tutorials but I have decided to write one in a post of its own. The benefit is that I could add to it later based on new developments and invaluable feedback. This tutorial is inspired by this thread:

Automation might come later.


Multiple exposure in GIMP

Creative Commons Licence by @afre.

A. Obtain sample images

I took 2 screenshots from Big Buck Bunny. If you aren’t familiar with the project, visit https://peach.blender.org/ to read about it and give it a viewing. License:

Big Buck Bunny
Copyright (C) 2008 Blender Foundation | peach.blender.org
Some Rights Reserved. Creative Commons Attribution 3.0 license.
http://www.bigbuckbunny.org/

450.jpg

456.jpg

B. The Workflow

_Multiple_ can be anywhere from 2 to 10+ images. I only used 2 here. The principle would remain the same. I am using **GIMP 2.10** by the way. You may follow along using the XCF: [upload wasn't successful – will try again later].

Each layer is a step in the workflow, starting from the bottom.
image

Step 1

**Open** (_as Layers..._). Choose a base image. I would say the one that is the most compelling. Since this is an animated film and I have only two images, it does not matter which I choose. However, as you iterate, I suggest you use the same image as the base. Here, we have **456.jpg** on top of **450.jpg**. **450** shall be our base.

Step 2

Change the layer blend mode to **Grain extract**. It could be another blend mode if you prefer, as long as it isolates the subjects well.

Step 3

Next we use the _G'MIC filter_ **Gradient norm**. The settings are in the layer name. Each number corresponds to a parameter in the filter's menu. Basically, we want a closed and sharp outline of the subject.

Step 4

As you can see in **Step 3**, the outlines are still faint. Use **Curves** to make them as distinct as possible. Squish the range so that it almost becomes a binary image (black and white with as little in between as possible).

image

Step 5

Use _G'MIC's_ **Fill holes** to solidify the subject as much as possible without making the subject larger. Again, the parameters could be found in the layer's name.

image

Step 6

Chances are that you still have holes. Not to worry. Fuzzy select the black, sharpen selection, invert it and then bucket fill the white. Sharpen is only useful if the selection has anti-aliasing, feathering or the like. You may want feathering, etc., but now is not the time for that. :stuck_out_tongue: Add it later if you wish.

image

Step 7

Now we have a mask that has the subject of both **450** and **456**. **Duplicate** the layer twice to get a mask for each. You don't need **450** for the compositing but it might be handy if you want to edit the subjects and backgrounds separately afterwards.

image

Step 8

Duplicate **450** and **456** and place them on top of the layer stack. **Fuzzy** select **Mask 2** (and **sharpen** selection). **Add Layer Mask...** → set **Selection** to **456** and **_voila!_** – you have arrived at the composite!

We have just doubled the squirrel threat!

7 Likes

After 8 logged edits and 50+ minor ones, I think I can call it a night. @patdavid @paperdigits feel free to proofread, make any adjustments or suggestions.

It sucks that the format kept on changing on me during the writing. I tried to rewrite various parts on the fly to fix things. Maybe I should have just published and then go back… I would still like to upload the XCF; fortunately, the other images are up now.

Having a low quality small laptop screen; arthritis in my hands; going back and forth between applications and making screenshots again and again certainly didn’t help. I will always appreciate the diligence of our most excellent tutorial writers!

As someone who writes instruction for a living, the best instructions read easily and seem effortless, but in fact took a lot of time and effort to produce. :slight_smile:

I usually try and get the images in, save the post, then edit & save every so often. Discuss is a little funky with less than stellar internet connections as well. I appologize that it seemed to muck up the photos, I did see that an hour or so ago.

Sometimes if the post is really long, I just write the body of it offline. For the main blog, we sometimes use https://hackmd.io or just plain old git

My initial read of your tutorial is that you need to break your steps down even further than you already have.

1 Like

Okay, I will try to flesh it out more.

You can use grey (neutral) as it mask

2 Likes

Thanks. I actually don’t use GIMP much, so my method has room for improvement. I improvise as I go. In fact, I improv’ed this tutorial. I have never done composites or written tutorials like this before. :joy_cat: As they say, learning by doing. :sunny:

1 Like

I want to do something similar to separate background of characters in old animations.
I will have to learn something of gmic

Thanks for the tutorial @afre.

You might be able to combine steps 3, 4 and 5 with G’MIC Contour Edges filters with a Smoothness 0 and a Threshold around 4 to 6.

1 Like

@Hebustetram Thanks. I haven’t gotten around to fleshing it out yet.