Expert: Scott Valentine - 4/2/2009

Question
I'm somewhat new to CS4 and I can't figure out how to do a the rainbow
effect on picture to the extent that I want. I have some pictures that are in
black& white that i would like to only add color to specific parts. I have links
to deviantart.com of the idea of what i'm going for.

I would like to achieve something like this...

http://pipper-SVK.deviantart.com/art/Rainbow-City-105611704

And for the flower I would like to try.

http://NessaRaul.deviantart.com/art/Flower-Rainbow-60654451

Any help on the topic would be great. Thanks
Nick

Answer
Hi Nick,

These are classic, wonderful effects. I'll spare you the backstory of how it was done 'in the day', and jump to the solution:

Color blend mode

In Photoshop, you can change the blend mode of layers so that the colors and pixels of one layer interact with the colors and pixels of the layer beneath. This blending relies on a variety of elements, so I encourage you to read up on blend modes in the CS4 online help files.

To get the effect you want, you will need to create a new layer above your image layer. In the simplest form, you will use the gradient tool to fill the blank layer - there is a rainbow preset you can use. Drag out the gradient so it fills the layer.

At the top of the layers panel, there is a drop-down box that typically says 'Normal'. This is where you can find your blending options immediately. In that drop-down box is an option for 'Color', near the bottom of the list. Choose that and see what happens.

This effect usually works best if you also create a Black and White adjustment layer, and convert the areas of interest to black and white. You can limit how the adjustment layer works by using its layer mask. Simply black out the areas you don't want affected, and leave the rest white.

The flower image uses this approach - only the petals are affected by the gradient, which implies that the rest of the area (the grass) was masked out.

If you are not familiar with these terms or techniques, let me know and I'll provide some links. Most of what you need, however, will be in the help files under the terms I've listed (they'll give you enough information to get started).

Please let me know if you have further questions, or would like some clarification!

-Scott