When you combine layers you are, in effect, changing the way pixels on the various layers unite with each other. This process usually gives us some cool, and often unusual, results. If you are looking to compose multiple-image artwork, blending modes can be a great way to accomplish that.
To start out with I'm going to use a Photoshop file that has two layers. One layer is an image of a field and the other layer contains a farm house. When you're playing with this yourself you can just use any Photoshop image that has two different layers, with something on each layer.
It's always a good idea to give your layers a descriptive name. Don't just leave each layer with it's default of Layer 1, Layer 2, Layer 3 and so on. When you're dealing with an image with 20 layers this becomes very tiresome when you're trying to figure out what's on each layer.
Step 1 - Rename your Layer Double-click the layer name in the Layers palette. A bounding box will appear around the words Layer 1. Type a new name and Press Return or Enter.
Note: You want to make sure you click directly on the layer name, otherwise you will open the Layer Style dialog box and you won't be able to rename the layer.
Step 2 To select your layer click on the eye icon on the newly-named Field layers and the image of the field appears in the image and the Farm House is hidden.
Step 3 With the Stairs layer selected in the Layers palette, click on the arrow beside the opacity field and drag the slider to 40%. Notice that everything on this layer - the stairs and the wall they are attached to becomes less opaque (more see-through).
Step 4 Lowering the opacity of a layer makes the artwork on that layer more translucent, so that the layers beneath it show through.
Step 5 Drag the opacity slider back to 100% so that you can see the Stairs normally.
Step 6 On the layers palette, click on the down arrow beside the field that says " Normal". By default, layer appear with a blending mode of Normal.
Step 7 From the drop down menu that appears, choose Hard Mix.
You should notice that the image changes quite dramatically.
Play for a few minutes and try out different blending modes to see how the image is affected with each one.
The Multiply mode is quite probably one of the most frequently used blending modes. It blends layers to create a darker color, except where there are white pixels. The white pixels will disappear.
When you have found a blending mode that produces an effect you like, click on the Stairs palette to select it. Click on the "Create a New Layer" button at the bottom of the Layers palette.
You now have a new empty layer which appears in the Layers palette just above the Stairs layer, but nothing should have changed on your image in the document window. When you add a new layer the layer is empty and transparent by default. We want to use this new layer to draw a border around the image you've been working on. The advantage to drawing on this new layer, as opposed to drawing on any of the other layers, is that it can be isolated on its own - turned on or off, transparency adjusted and other adjustments applied to the layer.
Make sure that the new empty layer is selected. Select the Brush tool from the Toolbox (or hit B on the keyboard). On the tool options bar, click on the Brush Preset Picker and select a rough looking brush. (I picked a Dry Brush Light Flow) and set the master diameter to about 100 pixels. On the toolbox, set the foreground colour to black by hitting "D" on the keyboard - this sets the foreground and background colours to their default - black and white. Start drawing around the edge of the image to create a rough border.
Rename the layer as "B order". (Yes, I know I'm nagging about the naming of layers but it's good practice!)
The benefit to drawing on this new empty layer is if you don't like your work you can turn it off without affecting your entire image. You could also reduce the opacity to see how that looks.
Take some time to try adding more layers to your image and play with the drawing tools. Select different brushes and colors and choose different blending modes.
I hope you enjoyed our intro to blending modes and opacity. Obviously the best way to find out how they all work is, of course, to play and check out all the different effects you can achieve.
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