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Special Effects - Combining Two Images

Updated: Sep 1, 2023

It is possible to combine two or more images together to create a scene from your imagination. Whether you are expressing yourself for artistic reasons, for your romantic partner or just for fun, it can be done. You don't even need to buy expensive software - you can do this with free and open source software called GIMP (GNU Image Manipulation Program). In this tutorial I will show you how. You will need to have GIMP downloaded and installed on your computer.

Taking the Photos

Take, generate or find the image of the scene you would like to insert into. Consider copyright implications if you found the image. The below is AI generated.

Take the photo of the object or person you would like to insert into the scene. Make sure you have the person's permission to use their photo. It should typically (depending on what you are trying to achieve) be a photo of the whole person or object, have no objects covering, be high quality, close up and ideally have a well contrasting background. If there are objects covering or the background is a bit blended (see below) it's not the end of the world - we can fix it, it just won't look quite as good and/or will be a bit more effort. Missing body parts are much harder to fix!

The below image has the whole object (me) and nothing covering but is not that high quality or close up and the sand kind of matches my skin colour. Oh well.

Get the Subject to Insert

Refer to cutting out objects in images if you don't already have an object with a transparent background.

Here are the instructions for copying using GIMP (you can use just about any image viewing program).

Open the image. Make sure only the layer you want to copy from is visible.

Choose the Rectangle Select tool.

Select the part you want to copy by dragging over it.

Go to the Edit menu and choose Copy. (Shortcut - on a PC you hold down Ctrl and press C, on a Mac you hold down the Command key and press C).

Place the Object in the Host Image

Open the image you want to paste into in GIMP. Choose Edit -> Paste as -> New Layer.

Great, but it doesn't look like I fit in! Let's fix that.

Use the Scale tool.

Experiment with dragging on the handles until it looks like the size you want. Heck, the size you want doesn't even have to be normal, depending on what you want to achieve.

Use the Move tool.

Move the object to where you want.

Cast a Shadow

It still doesn't quite look right, and that's not just my OCD! That's because we need to add a shadow. Here's how.

First, press on the anchor to confirm the new layer.

And zoom right in (bottom left menu). You may need to scroll in the editing area back to the object you pasted.

Managing the Selection

GIMP will only edit what you have selected on the active layer. Memorise this or lose hair! The layer with the white border is the active layer. In this case, we are going to use the Drop Shadow function, which uses the active layer to cast a shadow on the active selection.

A nice thing about GIMP is not only can you undo actions, you can undo changes to the selection with Edit -> Undo (or Ctrl - Z on PC, Command - Z on a Mac).

Another consideration is the layer boundary, which has a yellow border and is shown for the active layer. GIMP will not do anything outside this boundary.

Therefore, we may need to adjust it. Choose Layer -> Boundary to Image. Yellow border gone.

I'm not big enough to be casting a shadow on that waterfall in the distance, am I? 😛Therefore, let's tell GIMP to only cast a shadow on the rock. However, at the same time, we need to tell GIMP to make a shadow using the whole object. Fortunately there is a very quick way to select the object, which we will do first.

Click the Select by Colour tool.

Change the colour to Alpha and the threshold to about 30 (this will filter out the fuzzy bits on the edge).

Click on the object. That was easy!

Next bit is a bit fiddlier - we want to add the rock to the selection.

Make the background layer active and turn off the pasted layer.

Choose Free Select.

Hold down the Shift key and trace around the shape by dragging. You can release the mouse button and still continue, but if you drag on the small orange dot you will move the line. Move the mouse away from the dot to avoid this.

Keep tracing until you meet the object again. Click to add points where you don't need to trace, e.g. the ground around the rock as we don't want the shadow to reach there anyway. Make sure Shift is held down and press Enter.

Eliminate the hole or make other adjustments using the Free Select tool while holding down Shift. Here, no need to trace - just roughly click around the hole. To remove from the selection, hold down Ctrl on a PC, Command on a Mac.

Actually Make the Shadow

When you are happy with the selection, make active and show the layer with the object you pasted.

Choose Filters -> Light and Shadow -> Drop Shadow.

Play around with the settings until it looks how you want. I frequently do these:

  1. Turn off the link between X and Y offset (horizontal and vertical offset respectively)

  2. Play around with the X and Y offset

  3. Adjust the Blur Radius (the closer you are to the nearby feature, the sharper the shadow)

  4. Fiddle with the grow radius

  5. Change the Opacity (the closer you are to the nearby feature, the darker the shadow)

As my legs and torso will be casting different shadows, I will use the tool twice. Once for my butt and feet:

Press OK. Clean up the shadow here before placing another one.

And once for my whole body (you can just click anywhere on the image, it will stay on the Drop Shadow tool until you change it):

Clean Up the Shadow

I'm still not 100% happy with the shadow. With the pasted object's layer selected, we can use the eraser to remove some shadow. Use the Eraser tool.

Adjust the size and shape. We probably want the fuzzy circle to make smooth adjustments. Experiment with it and choose Undo if you make a mistake.

Add To the Shadow

If we like, we can draw extra shadow.

(Optional) Select the area you want to restrict shadow drawing to using Free Select. This can make it much easier.

To extend the shadow, use the Paintbrush. A fuzzy edge brush is probably better for shadows.

Final Look Over

Zoom right out to see how it looks.

Also choose Select -> None.

Looks good! Save the XCF file if you want to change it later. Also choose File -> Export As and save as a JPEG file.

Done! 🥳

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