Layers

What can layers do in Photoshop?

• Photoshop lets you build up an image using layers of graphic information
• Layers  get stacked on top of each other (and you can change the stacking order by dragging layers up or down).
• Exception: If you want to move the background layer (layer 0) you have to change its name.
• Layers let you isolate different parts of an image so you can work on one part of image without disturbing other parts (e.g., text).
• Making changes to your image in a layer lets you delete layers you don't like and keep the ones you like   
• Layers increase file size as pixels in each layer are merged with image.
• Only the Photoshop file format (PSD) preserves the information in the layers.
• When you compress an image you have to first "flatten" the layers.
• You should save a photoshop ("PSD") version of your image file before you flatten it in case you want to change it later.
• When you flatten an image you can choose to flatten only selected layers or all layers

How many layers?

• Every Photoshop image contains 1 or more layers. 
• New files (including scanned images) are created with 1 layer
• As you add layers to your image give them MEANINGFUL NAMES to make it easier to edit the image. 
• Layers are transparent (checked) until you put something on the layer.
• The Layers Palette lets you control the layers and their ordering.
• The eye icon in the left column lets you know that the layer is visible.
• You can hide or show layers by clicking the column
• When you flatten the image before you compress it, you can choose to include ALL the layers or only the VISIBLE layers.

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Selecting layers:

• You can select and edit one layer at a time (the active layer has a paintbrush next to it)
• You can ONLY work on the selected layer
• If what you are doing doesn't seem to work, check that the layer that you want to change is selected
• You can change the transparency/opacity of the layer by sliding the opacity slide, some some of your changes could be semi-transparent

Adding Layers:

• Can add layers from the menu command Layer, or from arrow at end of Layers Palette.
• "New layers" adds newlayer on which you can work. 
• For example you could add a "gradient" layer to change background by applying color gradient that will alter your image in several ways (darken, lighten, etc.)  The gradient palette lets you choose opacity of gradient + other options.
• Drag (or copy and paste) an image from another PS file onto an image you have open ("open") and a new layer is created for the open image. 
• You can then move the new image around and erase any parts you don't want with the eraser tool
• When you select the text tool and add text to an image, it goes into its own layer.

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Erasing parts of layers:

• Eraser mode block erases completely.
• Eraser mode paintbrush lets you set opacity so you can fade an image

Deleting layers:

• Delete a layer via menu option or layer palette arrow or drag into trash bucket
• The ability to delete layers you don't like lets you experiment more with your images

Transform:

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• Can rotate and scale any object on a layer via Layers>Free transform;
• Layers>Transform which lets you rotate or skew objects on layer.

Link layers:

• To link layers together, select one layer (with paintbrush in right-hand check box). 
• Then select right-hand check box for rest of layers, which displays a link. 
• Now if you move one of the layers, the linked layers will move with it -- useful when images in different layers have a definite positional relationship to one another.

Merging layers:

• You can merge all visible layers (with eye turned on) or all layers below a selected layer.
• Merged layers become one layer.

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Flattening Layers

• Flattening all the layers into a single layer greatly reduces file size.
• Save an unflattened version first, in case you want to change anything later.
• Flatten the image when you are finished
• Then you can save the file in multiple formats other than PSD, including BMP, JPG.
• Look at the difference in file size between the flattened and unflattened image (visible in the lower status frame)!
• To save images files as GIF files you have to change the color to indexed.
• Generally you only change color mode to indexed for photographic images if you want to make the files transparent GIFs, or if you have some other reason (GIF files lose a lot of image information, but take up less memory).

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Adjustment layers

• Let you apply global effects without permanently changing the pixel values in the image.
• On the layer palette choose New Adjustment layer. 
• Then select what kind of adjustment you want to make. 
• Hue will let you experiment with different levels of RGB without affecting actual image
• Brightness, contrast let you alter values
• Posterize lets you give image into a poster quality

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Duplicate layers:

• Use duplicate layers to allow you to experiment with a layer without doing anything to it directly.
• To add a Drop Shadow in older versions of Photoshop you had to:
• Create a Text layer (double click on text tool), type in text.  Rename layer to text 
• Select Text layer, and create duplicate layer. 
• Change color of text. 
• Position duplicate layer behind text layer (below it) and move text to creat shadow. 
• Can then link 2 text layers together and move them wherever you want on image. 
• When finished, flatten.

Now you can create text shadows with Layer>effects or with a default action (cast shadow>type)

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the Type tool creates a Text Layer

• Check the Anti-Aliased check box if you are compositing this text with other imagery to create a smooth transition without harsh edges.
• Check the Auto Kern check box to kern characters (sets them up as equidistant).
• You can add Layer Effects, such as drop shadows, glows, bevels, and embossing to any layer, including Text via the Layer>effects> command.
• When you are finished with a text layer you need to render it to convert the outline text into a pixel bitmap via Layer>Type>Render.
• After you render it you cannot edit the text again so you may want to save a version without rendering in case you want to easily change the text later.

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