Compositing

Here's how to merge elements from different photographs into one.

First, make sure you've downloaded and installed The Gimp.

Here are the two photographs we're going to use, taken from FirstWorldWar.com

Here's the final image:

Getting Started

1. Download trenches.xcf.zip which contains the two source photos on named layers (or copy it from /students/files/trenches.xcf into your folder)
2. Open 'trenches.xcf' in Gimp
3. This file contains two photos - a trench and a soldier throwing a grenade. The photos are on separate, named layers
4. Open the Layers palette (ctrl-L).
5. Click the eye next to each layer to show/hide the two photos

Remove the background from the soldier photo

1. Right-click the 'soldier' layer, select 'Add Layer Mask' (white, full opacity)
2. Select the paintbrush (P) tool
3. Dialogs > Brushes (ctrl-shift-B)
4. Choose a fuzzy 19-px brush.
5. Now 'paint' with black onto the soldier layer's mask. Wherever you paint with 'black', the 'soldier' layer will become transparent. If you rub out too much, paint it back in with 'white'. Use the 'x' key to switch between black & white.
6. No need to be too accurate yet, just clear away the background

Resize & position the soldier layer

1. Select the 'Move' tool (M)
2. In the Layers palette, click on the layer itself (not the mask)
3. Drag the soldier to the trench with the two helmets on posts
4. Select the 'Scale' tool (shift-T). In the options below, select 'Keep aspect' so the grenade thrower stays in proportion
5. Drag the soldier layer until it's about the right size
6. View > Show Layer Boundary to hide the yellow/black layer edges

Finishing touches

1. View > New view to create a second copy of the image. Keep this one at 100% (1) and zoom the other window (-/+) to clean up your mask
2. You may also want to adjust the contrast to make the soldier 'fit' the background better (Layer > Colors > Brightness/Contrast)
3. Finally, open Layer > Colors > Curves on the background layer and pull the top right and bottom left ends of the line inwards to where the histogram starts to fix the 'dullness' of the photo. This makes the blacks blacker and the white whiter!

Compositing tutorial on You Tube

• Digital Compositing 1 - what is compositing?
• Digital Compositing 2 - masking images to extract the parts you want
• Digital Compositing 3 - layering your masked images
• Digital Compositing 4 - finishing touches to improve realism

Compositing Examples

• Horse on a misty morning

Related pages: The Gimp

Category: ICT

Author: Mr Kershaw