The ability to take several images and blend them into one seamless piece of art is a core strength of Adobe Photoshop (800/833-6687, www.adobe.com ). The secret to achieving a flawless blend lies in the flexibility and power of Photoshop's layer masks, which allow you to make parts of a layer fully or partially transparent, selectively revealing the layers beneath.
Using layer masks is simple -- if your graphics contain clean, high-contrast edges. Alas, most images aren't that considerate. Take the artwork below, for example. The original image -- a man with wings set against a blue background -- contains semitransparent areas as well as blurred and faint edges, making the winged figure a nightmare to select. If you ignored the transparencies and blurred edges, the resulting selection wouldn't blend gracefully into the target background of sun-streaked water.
Macworld Design Associate Amy Conger solved the problem by combining several blending methods on her layer mask, thereby creating multiple levels of opacity. (In a layer mask, opacity is represented by shades of gray: black is totally opaque and white is totally transparent.) The end result is a seamless blend of two images.
Make a Rough Layer Mask
Amy first placed the images into separate layers (with the angel image on top). To quickly select the angel's unwanted background, she set the magic-wand tool's tolerance to 36; to prevent selection of blue pixels inside the figure, she selected the Contiguous option. She then shift-clicked on the areas around the figure and turned the selection into a layer mask (Layer: Add Layer Masks).
Clean Up the Edges
The initial layer mask covered too much of the angel in some places and too little in others, so Amy used the paintbrush tool to clean up the mask's edges. She made the image and the mask (represented by the red areas) visible at the same time so refining the edges accurately would be easier. Where the mask needed adjustment, Amy painted with white to remove excess masking and with black to enlarge the mask.
Blur the Edges
While the edges of the original images aren't sharp, they aren't uniformly blurry, either. To preserve these subtle variations in focus, Amy blurred the mask's edges manually with the Blur tool. (She didn't use the Blur filter because it would have affected the entire mask equally.) Amy set the Blur tool to a soft-edged brush and used pressures ranging from 50 to 100 percent.
Smudge the Edges
To preserve the illusion of motion around the figure's hands, Amy used the Smudge tool to manipulate the mask's transparency. The Smudge tool pushes at pixels much as your finger smears charcoal on paper, spreading the edges and lightening them as you go. She set the pressure to 25 percent and selected Normal mode, and then she delicately pushed and pulled the mask's edges to thin out the transparency.
Lighten Translucent Areas
Amy wanted the inside of the wings to be translucent so the angel would have a sense of depth. She first switched from the layer mask to the original image. With the magic-wand tool set to a tolerance of 24, Amy selected the inner areas of the wings. She then returned to the layer mask and filled the selection with a light gray to add semitransparency.
Final Layer Mask and Image
Thanks to the finely honed layer mask (lower righthand corner), the final combined image looks like it's always been this way.
TERRI STONE is the senior editor of Macworld 's How-to section.
Sunlight in the Water © 2001, Corbis Corporation/Norbert Wu; Man with Wings © 2001, Corbis Corporation/Jose L. Pelaez