A popular trend these days is using color selectively in photographs. You have seen a black & white photo that only has one object that is still full or partial color. This is a very dramatic effect that is very simple to achieve. Here’s how you do it.
First a quick disclaimer, as with all fantastic effects, the first step is to have a great photo. While this effect can greatly improve a relatively blah image, try to avoid using one. Okay, with that said, choose your image. Next creative a layer above it and change its Blend Mode from Normal to Color. Next select the Brush Tool and give it a soft edge. To do this on the fly, simply hold down the Shift key and use the Left and Right Bracket keys. The Left Bracket key makes the edge softer, and the Right Bracket key make the brush’s edge harder. Also remember that the Left Bracket key makes the brush tip larger and the Right Bracket key makes it smaller.
Next select black your foreground color and change the Opacity to about 60% – 80%. This will allow you to “build” the effect. There’s no rule saying you can’t just start at 100%, but dialing it down abit will give you an opportunity to experiment. It’s also a good idea to zoom in close to see the edges of the elements you are painting and be a little less sloppy. Then just start painting on the layer above your photo’s Background layer and watch the magic of the effect take place. By changing the Blend Mode to Color, Photoshop will use only the Hue & Saturation of the color and leave the Brightness alone. By painting with black we are effectively de-saturating the colors in the image layer below.
Remember this is just the beginning. If you want your image to have a sepia tone, just adjust the color on your brush to a color of your choosing. Experiment with the different base elements of this technique to come up with a unique style of your own. Also remember, you don’t “have” to stay within the lines. Happy Photoshopping!