Adjustment layers are a special feature of Adobe Photoshop Elements that allows you to make removable and editable adjustments to images. Open this image and then click the Adjustment layer button on the layers palette..
When you click the button, you should then be prompted to choose the type of adjustment layer you'd like to create. For starters, we'll work with Levels and Hue/Saturation.
Go ahead and make the levels adjustment we did before (blue channel to add yellow). You'll now notice that there is a new "layer" in the layers palette. This layer works as an independent set of data that is modifying the image. Because this layer is independent of the image layer, it can be changed, deleted, modified without any actual adjustments to the image and therefore no compromises in quality.
Furthermore, the layer can be set to varying degrees of opacity.
One of the most amazing aspects of adjustment layers, however, is the its "mask" feature. This is a special image joined to the adjustment layer that allows you to paint on it and thereby control where the adjustment will happend and where it will be hidden from the final image.
Overlay layers is a term that I made up to describe a certain process of blending two layers together. Layers have blending modes which can change the behavior of how different layers interact with other layers. By changing the blending mode of a layer, the different ways it can blend with the image layer can be striking.
For instance, let's create a blank layer (which is by default completely transparent), and paint some yellow or orange color over the trail in our image. To do this,
Another important technique that uses blending modes, is "burning" or darkening skies in a realistic way. Click this link to view a tutorial on this technique. Burn sky with overlay layer
Also, here's an image that can help.
Other colored layers can be added to sunset images to really enhance the colors. You can also blend copies of the image itself for other special effects. Download this image.