Understanding layers

In this post i will talk about photoshop layers. Adobe introduced this for the first time in Photoshop version 3. Simply put, a layer is an image on top of another (the background image is the first layer). If the blending mode is set to Normal, the top layer will become visible (the items in it) and the layers below him will not show up (unless the items in the first one are smaller than those you can find in the other layers)

For example, let's open a new document in Photoshop CS4 (width and height don't really matter). Using the Ellipse Tool, draw a circle like the one below, filled with black (hold Shift to draw a perfect circle). Notice that another layer was created in the layers windows (press F7 if it doesn't show up)

Now, draw a blue rectangle using Rectangle Tool. Another layer was created. Right now, we can not see the black circle, but if we change the blending mode to Multiply it will show up (a mixture of the layers appears. You can use different blending modes to obtain different effects)




If you set the blending mode to normal, and switch the layers between them, the black circle will show up on top of the blue rectangle.
Layers are very useful when you prefer working on a copy of an image, for example. You can just duplicate the current layer (Layer - Duplicate layer, or drag it to the Create New Layer button) and start working on it. If you don't like the results, you cand always delete the layer (drag it to the Delete Layer button) and start all over again, making another duplicate.