This seldom-used command lets you combine two open images (as long as they’re exactly the same size) and pick a blend mode and opacity at the same time. Although you can do the same thing using layer blend modes and opacity, the Apply Image command lets you pick which channel Photoshop uses to do the blending, as shown in Figure 1.
To use Apply Image on two RGB images, follow these steps:
- Open the source and target images as separate documents.
The source image is the one you want to blend with another image; in Figure 1, that’s the crowd shot. The target image is the one where Photoshop will do the actual blending; in Figure 1, that’s the photo of the motorcyclist.
- Duplicate the target image’s Background layer.
Since the Apply Image command changes the current layer’s pixels, it’s best to copy your image first so you can go back to the original or add a layer mask to reveal part of it. To duplicate the layer, press command+J (Ctrl+J on a PC).
- Choose Image➝Apply Image and pick the source image.
In the resulting dialog box (shown in Figure 1), choose the source image from the Source pop-up menu. If you don’t see the image you want in the list, it means your source image isn’t exactly the same size as your target image. In that case, press the Esc key and jump back to page 236 for the scoop on resizing. When you’ve got your images the same size, your source image appears on the list.
- In the Apply Image dialog box, pick the layer and channel from the source
image that you want to blend with your target image.
If your source image has more than one layer, you can specify which one you want to use in the Layer pop-up menu. The same goes for channels: You can use the composite channel (RGB) or a specific channel (red, green, or blue). Turn on the Invert checkbox if you want to reverse (flip-flop) the color info in the channel (turning what was light dark and what was dark light).
- Pick a blend mode and opacity.
The Apply Image dialog box’s Blending pop-up menu lets you choose from the full range of blend modes (see the previous sections), plus two extras: Add and Subtract. In Add mode, the RGB color values of the source image’s pixels are added to the target image’s pixels in the same location (making colors brighter and more intense in those areas). In Subtract mode, the RGB color values are subtracted (making colors lighter and less intense). Pure white and pure black pixels remain unchanged in both modes.
If you choose either Add or Subtract, Photoshop adds two more fields to the Apply Image dialog box: Scale and Offset. Scale makes Photoshop average the added or subtracted RGB color values by the number you enter here (in this case, a number between 1 and 2). For example, if you enter 2 in the Scale field, Photoshop divides the color values that it adds or subtracts by 2. The Offset field lets you alter the brightness of the resulting RGB color values by selecting from a scale of –255 (black) to 255 (white). You’ll probably use Add only if you’re working with two versions of the same image, maybe one that’s too dark and one that’s too light. And you’ll probably never use Subtract unless you’re going for a really funky, artsy effect.
- If you like, turn on the Preserve Transparency and Mask checkboxes.
Turn on Preserve Transparency if you’ve got any transparent pixels on the target layer that you want to keep transparent. Turn on the Mask checkbox to hide the source image from the lightest areas in your target layer (so you won’t see the source image in those spots), and apply more of the source image to the darker areas.
- Click OK and enjoy your collage.
Though you can blend only two images at a time, there’s no rule against using Apply Image on the same target image with different source images to blend several images together. And because Photoshop literally applies one image to another when you run this command, you won’t increase the number of layers in your target document. If you’re concerned about file size—maybe you have limited hard drive space or a slow computer—this method produces a smaller file than it would if you combined all the images into one document and then changed the blend mode of each layer (or used layer masks).
You can also use Apply Image to combine channel information within the same document. For example, if you want to add more details to your image, you can choose the same document as both the source and the target image and then select the green channel from the pop-up menu. The result is similar to what you’d get if you copied and pasted the green channel into your Layers panel and then changed its blend mode and layer opacity to what you enter here in the Apply Image dialog box. The only difference is that using Apply Image doesn’t add a layer to your document.
Learn more about this topic from Photoshop CS5: The Missing Manual.
Photoshop is the world's most widely used photo-editing and graphics program. But with all its fantastic new features and options, Photoshop CS5 can bewilder even the most seasoned professional. Packed with tips, tricks, and practical advice, this Missing Manual teaches you everything you need to know to edit photos and create beautiful documents in Photoshop -- whether you're a beginner or a seasoned pro ready to try advanced techniques.