Gotta add to this...

One of my favorite little tricks is something that was added in Photoshop 5.5 for Windows, 6 for Mac. It's under the Adjustments sub-menu (you know, where the Levels are located?). It's further down this list...

This one's called Gradient Map. What it does is more or less the same thing as the GIF color tables, except that it's not limited to 256 colors. It converts the image's luminosity, which ranges from 0 (black) to 255 (white), to whichever gradient you choose or design - and applies it over the entire image. What this means is if your gradient ranges from black to white, the result will be a grayscale image.

What's more interesting is if you try it with some actual color...so I've attached an image with some various gradient maps applied...the first is black to white. The next is the same black to white with a hazy, muddy blue stop added at 50%. The next is the chrome gradient, which ships with Photoshop. The last is a different kind of gradient, a Noise rather than a Solid gradient which works a little strangely, but if you play with it, you'll understand what it does.

The way you actually USE the Gradient map is as such:

Go to your Image menu, follow down to the Adjustments submenu (second one down). In the Adjustment menu, near the bottom, select 'Gradient Map...'

When the Gradient Map dialog opens, your image instantly changes reflecting a preview of the gradient displayed (if you don't play with gradients often, it's set by default to 'foreground to background.' If the foreground to background colors aren't at their defaults, your image WILL look wierd.). Click on the gradient itself to bring up the gradient editing dialog, the preview will continue to reflect the gradient as you edit it.

I won't go into how to use the editing dialog here because, firstly - it's pretty self evident if you're familiar with Photoshop and secondly - this is getting to be kind of long as far as add-ons go. However, if anyone has any questions, post a reply or email me at my renderosity address (i.e. click on my name and send an email).

Anyone able to stump me with a Photoshop question gets a pizza.