Adobe Photoshop Basics
    + Layers and History palette

Photoshop lets you organize artwork on separate transparent layers. Think of layers as a stack of acetate sheets one on top of the other. Where there is no image on the sheet, you can see thru the sheets laying below, and behind all the layers is the background.

If the Layers palette is not visible:
Go to Window > Show Layers
NOTE: Images with no background, as well as images with layers can ONLY be saved in the Photoshop Format

The graphic to the right displays the layer palette of the document on the left.

The layers palette lists all the layers in an image, starting with the topmost layer.

Note that the text has a separate layer as well as the UN logo and the background image. You can see the small thumbnails of the content for reference while using layers. In the case of text layers, the icon for type appears as thumbnail, and the text serves as name for the layer as well.

Layers palette description

A- Show/Hide
B & G- Paintbrush icon and highlighted layer: indicates the layer is active
C- Link/unlink
D- Add a New layer
E- Delete layer
F- Layer Content Thumbnail
H- Palette Options
To change the order of layers:
1. In the Layers palette, select the layer you want to move
2. Drag the layer up or down to the desired position within the palette.

Linking Layers
By linking two or more layers you can be able to move their contents together as well as perform certain tasks like scaling and aligning.

To link the layers:
1. Select the layer
2. Click in the column immediately to the left of any layers you want to link to the selected layer.

To change the name of a layer:
1. Click on the palette properties arrow (Letter "H" on graphic)
2. Select Layer properties

You can also assign a color to the layer in the palette if you need more organization or to highlight a specific layer.

Correcting Mistakes using the History Palette

As most of other editing software, Photoshop also uses the command CTRL Z to undo the last operation done. However you only have ONE time undo, using CRTL Z. The good news in Photoshop to help you correct mistakes is the History palette.

The History palette lets you jump to any recent state of the image created during the current working session. Each time you apply a change to an image, the new state of that image is added to the palette.

To revert to a previous state of the image click the name of the state on the History palette

Here are some guidelines to help you use the History palette:

1. Changes done to Photoshop's display interface, like preferences and palette settings are not recorded in the History palette. Only changes applied to your document will be collected in the palette.

2. By default the History palette records the previous 20 states, older states are automatically deleted in order to free memory for photoshop.

3. Once you close and re-open a document, all states and snapshots of the last session are cleared from the session

4. States are added from the top down.

5. Each state is listed with the name of the tool or command used to edit the image.

To reverse all changes made to the image since it was last saved:
Choose File > Revert, and click Revert.

History palette

This example shows the steps taken since the opening of the document.
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