Have a digital photo that you want to manipulate but don't want to destroy the original? You could accomplish this by making a copy of the original and working on that. Or, you can use Adjustment Layers in Photoshop.
Adjustment Layers allow you to apply various types of adjustments to the original photo sitting on a layer below your new Adjustment Layer without directly changing the original photo. It's kind of like looking at the world through a pair of sunglasses. The world takes on the hue of your sunglasses (green, brown, blue, gray) but the original world itself hasn't changed -- only how you're seeing it. Same thing with Adjustment Layers.
For example, let's take a photo
And add an Adjustment Layer of Hue/Saturation and set Saturation to -100 (remove all the color) -- I now have a black and white photo.
But I do miss the color and here's where I stepped away from Adjustment Layer and added in some other cool tricks. First I copied the original photo onto another layer *above* the Adjustment Layers. I then reduced the Opacity for that layer (made it see-through) so the black and white photo is also visible:
The color is subtle; maybe too subtle. So I again copied the original photo onto another layer, placed that layer above all other and deleted everything in the photo *except* the pink flowers:
I think I may have ended up close to the beginning, but it's a start. :) Here's my layer palette showing the different layers mentioned above:
Now, flowers may not be your thing, but this will give you a taste of the cool stuff we'll be doing with digital photos this fall.