Overview
Layers, within Photoshop, are a power means of organizing and manipulating specific parts of an image. Here is a brief overview of layers, their uses and how to isolate them.
Source: Michael Brown, SimonSezIT.com
Visibility, Ordering and Combining Layers
Layers allow for specific parts of an image to be altered without affecting other layers. This video shows how to change the visibility of a single layer, change the order in which they appear, and combine multiple layers with transparency into a single layer.
Source: Michael Brown, SimonSezIT.com
One concept overlooked by this video is the ability to group layers.
Rather than flattening multiple layers (a destructive method), a better practice is to create groups of layers. To group layers, select the layers you wish to group, locate the drop down menu next to the “Layer” panel title and select “New group from layers.” This will allow the layers to be edited individually but moved together in the stack.
Tip: When a layer is made invisible, the exported version of the file will not show that layer. This is an easy way to rapidly create multiple versions of a project without saving them as different files. Just remember to include groups of layers.
Opacity and Blending Modes
Opacity and Blend modes are fundamental layer qualities that determine how layers interact with those below them. Opacity, like transparency describes how visible an object is. Think of opacity as seeing a glass half full as opposed to transparency which sees it as half empty. Blending modes build on the opacity concept by isolating specific pixel ranges to leave visible in an image. Watch the following video for some great basics and quick tips on how to use transparency and blending modes.
Source: Deke McClelland, Lynda.com
For a deeper look at blending modes with more great tips, please see this video by Aaron Nace from Phlearn:
Source: Aaron Nace, Phlearn.com
Transforming Layers and Smart Objects
At some point in your Photoshop experimentation you will most likely have to resize a layer independently of the entire canvas. This could be because you are combining images that are different sizes or you may need to exaggerate size and shape. This video by Lynda.com’s Michael Ninness breaks down all you need to know about Free Transform mode.
Source: Michael Ninness, Lynda.com
It is important to note that when you transform an image you are constrained by the pixel information held within the image. If you have a low quality image and try to increase its size, the image will become pixelated. Alternatively, if you apply a transform, such as making an image smaller, you lose pixel information. In this case if you attempt to increase the size of the image again, just as before, the image will become pixelated. One way around this is to convert an image to a smart object. The basic principle here is that you are wrapping a container around the image to maintain all of the pixel information. See this video by PeachPit.com for more information on Smart Objects.
Source: Dan Moughamian, PeachPit.com via Adobe.tv