Basic Compositing

One of the coolest things about Photoshop is the way it allows us to take multiple images and combine them into one composite or collage. Rather than using the digital equivalent of scissors and glue, Photoshop lets us blending images together in beautiful and creative ways.

There are a variety of techniques for blending images. We'll start with a look at one of the simplest. Open a pair of images that you'd like to join. We'll use a couple of outdoor shots. You should make sure that the color mode of the documents matches and, as in this example, the bit depth. (Both are adjusted with the menu command Image> Mode.)

The next step is to put them into one document. Since they're different sizes, we could use the menu command Image> Image Size to resample one or the other. However, since we're working at low resolution, we'll simply scale when ready.

Copying an image from one document to another is quite easy - simply drag from the Layers palette of the source document onto the window of the second image. If the source image has multiple layers, they can be dragged one at a time or the image can be flattened first. Holding down the Shift key while the mouse button is released will center the dragged layer in the destination document.

Once the layer is copied, the original source document can be closed.

In the destination image, our work image, we now have two layers. As you can see by the bounding box, the difference in image size is considerable. (Note that "image size" refers to the pixel dimensions of an image, not the print size. When you look in the Image Size dialog box, think in terms of the pixel dimensions at the top section, not the print dimensions in the lower part.)

Command-T/Control-T puts us in Free Transform mode, which allows easy resizing of the image. (Make sure that the new layer is the active layer in the Layers palette.) Holding down the Option/Alt key allows us to resize with the image growing in all directions from the "point of origin," that target-shaped symbol in the center of the image. (The point of origin can be moved anywhere inside or outside the bounding box to change the spot from which you transform.) Adding the Shift key prevents distortion while resizing by constraining the width-height ratio of the image while you drag. In Free Transform mode, you can also reposition an image by clicking within the bounding box and dragging. Press Return/Enter when you've scaled and moved as desired.

We can also scale and move the lower layer to change the relative proportions. The upper layer can be hidden by clicking the eyeball icon in the Layers. Remember that you can't scale or move a layer named Background (with the name in italics). To change a background layer to a regular layer, Option/Alt-double-click the name in the Layers palette and rename it.

Now that the two images are together and sized, they need to be positioned. Lowering the opacity of the top layer allows you to see what you're doing as you reposition the layers. (Make sure that you click on the top layer in the Layers palette to make it active before reducing opacity.)

Once the images are in position we can do the fun part, the actual blend. Right now, the two layered images have a hard border. One stops, the other starts.

We'd rather have a nice, gentle fade between the two images. Remember that we're working with the simplest technique at this point. Select the Eraser tool in the Toolbox. In the Options Bar (or the Brushes palette for Photoshop 5 and 5.5), select a huge soft brush. (The size will depend on the size of your image.) Click on the brush icon to open its specifications.

Make sure that the brush hardness is set to zero. That ensures the softest possible brush and gives us the greatest region of transition between the two images.

Position the cursor at the top of the image where the two pictures meet. (In this figure, the diameter of the cursor is represented by the dashed arc.) Click once.

Move the cursor to the bottom of the image where the two pictures meet and Shift-click. Holding down Shift forces the Eraser to do its work in a straight line between the two points that were clicked. Hiding the lower layer shows the nice even fade created by the soft-edged brush.

The transition between the two images is far more appealing that the hard edged border we had a few moments ago.

Tip: The Eraser tool can be set to a lower opacity to emphasize the transition, and it can be used multiple times, too. In addition, no one ever said that the transitional line had to be straight.