Photoshop images can be composed of more than one layer. Layers are like sheets of transparent film on which pixels are painted. Layers may be edited separately and individual layers can be made visible or invisible. Layers can be rearranged; their opacity may be changed; their blending mode can be altered, providing different overlay effects. Be aware that each new layer adds a significant amount of information to your file size.
Once selected, a group of pixels can be copied and pasted within its original image or into a new one. The act of pasting creates a new layer (see Windows > Layers).
A multi-layered image can be flattened to save file space and reduce printing time, but the flattened layers cannot be separated. For this reason, it’s good practice to choose File > Save As before flattening layers in a Photoshop image.
LAYERS PALETTE BASICS:
Make a layer current by clicking its name in the Layers palette. Any actions you perform will (in general) affect only the current layer.
Click on the eye symbol in the Layers palette to make a layer invisible or visible.
Change the opacity of the current layer by sliding the bar at the top of the palette. (Note: you cannot change the opacity of the Background layer.)
Change the display order of layers by dragging them up and down on the list.
LAYER BLENDING MODES:
Normal assumes that the top layer is opaque, unless adjusted by some other means (e. g., the Opacity setting in the Layers palette).
Multiply treats white pixels in the top layer as transparent. 50% white pixels are treated as 50% transparent, and so on.
Screen is exactly the opposite of Multiply. Black pixels in the top layer are treated as transparent.
Overlay combines the effects of Multiply and Screen. 50% (gray) pixels in the top layer are treated as completely transparent. Dark pixels become darker and light pixels become lighter.
To add a new layer: In the Layers palette, choose Layer > New Layer and give it a name. By default, new layers are totally transparent in Photoshop until you paste something onto them or paint on them.
To combine layers: In the Layers palette, choose Layer > Merge Visible to combine the visible layers onto the current layer.
To make the entire image into a single layer: In the Layers palette, choose Layer > Flatten Image.
COPYING BETWEEN LAYERS:
1. Activate the layer you want to copy from and make the selection. Choose Edit > Copy.
2. Activate the layer onto which you want to paste the selection. Choose Edit > Paste. Photoshop will automatically create a new layer above the current layer.
3. (Optional.) Click on the new layer in the Layers palette and choose Layer > Merge Down. (This combines the new layer with the layer immediately below.).