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 Photoshop CS3 Scripting Basics     12

The 

History State

 class is a palette object that keeps track of changes made to a document. Each time 

you apply a change to an image, the new state of that image is added to the palette. These states are 
accessible from document object and can be used to reset the document to a previous state. A history 
state can also be used to fill a selection. For more information on history objects, see 

.

In AppleScript, if you create a document and then immediately try to get history state, Photoshop 
returns an error. You must first activate Photoshop—make it the front-most application—before 
you can access history states.

The 

Document Info

 class stores metadata about a document. Metadata is any data that helps to describe 

the content or characteristics of a file. For more information on document info, see 

.

The 

Path Item

 class represents information about a drawing object, such as the outline of a shape, or a 

curved line. The 

Sub Path Item

 class is contained in the 

Path Item

 class, and provides the actual 

geometry of the shape. The 

Path Point

 class contains information about each point in a sub path. See 

The 

Preferences

 class allows you to access and set the user preference settings. See 

The 

Notifier

 object ties an event to a script. For example, if you would like Photoshop CS3 to 

automatically create a new document when you open the application, you could tie a script that creates a 

Document

 object to an 

Open Application

 event. For more information on notifiers, see 

.

The 

Count Item

 object provides scripting support for the Count Tool.

The 

Color Sampler

 object provides scripting support for the Color Sampler Tool.

The 

Measurement Scale

 object provides scripting support for the new Measurement Scale feature that 

allows you to set a scale for your document.

The following table provides describes how each object relates to the Photoshop CS3 user interface.