Of all weather phenomena, rainbows are the most beautiful and colorful, and carry the mythical promise of pots of gold. Unfortunately, capturing a rainbow with a camera requires a huge amount of luck—it's another classic example of the right-time, right-place school of photography. Luckily, with Photoshop, it's not difficult to add a rainbow to an image after the fact.
In this example, we'll use the Gradient tool, which includes a ready-made rainbow gradient. To get more realistic results, we'll use the rainbow gradient in conjunction with a black-to-transparent gradient.
So, no more chasing rainbows—it's Photoshop to the rescue!
1 The ideal candidate for a rainbow effect is an image that has a dark, dramatic sky, contrasted with shafts of sunlight.
2 Begin by adding a new layer to the image (Ctrl/Cmd+Shift+N), and call it "Rainbow" This will help us position the finished rainbow. Now choose the Gradient tool from the Toolbar. Click in the Gradient Picker in the Options bar.
3 Click the small, right-pointing arrow in the top right of the Gradient ...