This comes from the Lightsource Podcast, specifically from the guest Kirk Voclain. I just used it when working on the images that are at the top of my pages and really liked it. But I had to go listen to the podcast again to find out the specifics so I thought I’d write it down. And if I’m going to write it down, I might as well blog it.
Take the image you want to make pop and open it in Photoshop.
Make a Levels Layer
Hold the Option key (mac) down and click on the black shadow slider. When you do the whole image will turn white. Then slide until you just start to see the eyes and back off a little.
Now Option click the white/highlight slider. The whole image will go black. Slide until you just start to see any red in the image.
That’s it. Look at your preview on and off to see the difference.
As an aside, if you want to know what your image is going to look like in Firefox, go to Assign Profile and say don’t color manage the image. Then go to proof setup and select WindowRGB. That’s what your image will look like. Now adjust your images color.