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Workflow Techniques #102

An Introduction to Photoshop Scripting

essay by xbytor

 
 

Introduction

Photoshop provides a number of tools that aid in automating many tasks involved in image editing. This article provides an introduction to one of the more powerful tools at your disposal: scripting. A couple of examples are presented as is a list of resources that will help should you decide that scripting should become a part of your Photoshop toolkit.

An Overview of Scripting in Photoshop

A script, at its most basic, is a text file containing a set of commands. Batch/Command files in WinXP and shell scripts in Unix-based systems are both examples of scripts that most people are familiar with. In the case of Photoshop, the commands that are available make it possible to manipulate image files.

If there was an English language interpreter in Photoshop, the commands might look something like:

Rotate the current document 90° clockwise.
Flatten the layers.
Save the document as a web jpeg file at quality level 8.

As readable as this may be, the ambiguity inherent to the English language makes it a bad choice for scripting. Fortunately, Adobe provides three other languages (AppleScript, JavaScript, and VBScript) for scripting Photoshop.

The next two sections discuss when scripting is appropriate (compared to other techniques) and what factors you need to consider when deciding what the best language will be for your scripting tasks.

When is Scripting Appropriate

When faced with a repetitive task in Photoshop, there are a number of different ways to simplify the task. Some solutions are more difficult than other, but they all have a place. However it is important to remember that scripting is superset of the Action and Batch functionality already present in Photoshop. Anything you can do with Batch and Actions you can also do in a script. Additionally, scripting puts a wider array of tools and techniques at your disposal.

This is a useful checklist to go through when trying to optimize a repetitive task. This first solution is easiest, the last is the most complex.

1.Do it manually. This is the simplest solution. It's appropriate when you only have to do something a few times and the cost of finding or implementing another solution is higher than the cost of just getting the task done.

2. Use an automation plugin. There are several automation plugins that come with Photoshop (under the File->Automate menu) that may take care of the problem. There are also a wide variety of 3rd party plugins available online. One of these may be what you need.

3. Use an Action. Photoshop provides some useful Actions and there are many thousands of free and commercial Action sets available on web sites all over the Internet.

4. Use an existing script. You can find a lot bundled with Photoshop (under the File->Scripts menu) , on Adobe's site, and elsewhere on the web.

5. Record an Action. Many times the problem you are trying to solve is very specific to your workflow or to some set of images that you're working on. Existing Actions or plugins may not do what you need. The ability to record, replay, and batch Actions let's you develop a set of automation tools that address your exact set of needs.

6. Write a script. Although quite a bit more complex than recording an Action, this technique is also considerably more powerful. Anything you can do in an Action can be done in a script. There is at least one Action file to JavaScript translator [see Resources] that illustrates this fact. But, in addition to all of capabilities of Actions, you also now have the ability to branch and iterate automatically. Examples of this will appear in the next section.

7. Write an automation plugin. While this is the most complex solution it is, ultimately, the most powerful. Writing in compiled programming language (i.e. C++) gives you far fuller access to Photoshop's runtime environment and makes it possible to implement highly complex solutions with good performance.

In the end, it is not uncommon that a highly automated workflow uses some combination of Actions, scripts, and plugins to accomplish the required tasks. Understanding what the available tools are capable of and where there are appropriate goes a long way towards this end.

Selecting the Appropriate Scripting Language

Photoshop can be scripted from a number of different languages. Specifically, these languages are:

  • JavaScript (JS) – Available for both Windows and Macintosh computers. It provides a standard core JavaScript implementation with extensions for programming Photoshop. This has nothing to do with the Java language except having a similar name. Also, this JavaScript interpreter has nothing to do with web browsers, although it can be used to generate HTML pages.
  • AppleScript (AS)– Available only on the Macintosh.
  • VBScript (VBS) – Available only on Windows.
  • OLE interoperable languages – Available only on Windows. Includes VisualBasic, C#, and other languages. This is only really an appropriate choice if you have a good background in OLE programming and you have an existing body of code that you plan on utilizing.

How you select a language for scripting depends on your needs, your experience, and your platform. Here are a set of relevant questions that you should ask yourself when selecting a language.

1. On what platform do the scripts have to run? On Windows, you have a choice between VB and JS, on the Macintosh you have a choice between JS and AS. On both Windows and Macintosh computers? If so, your only choice is JS.

2. Does your script have to work with other Creative Suite applications? JS provides the best support although AS and VBS can be used to some extent on their respective platforms.

3. Does your script have to work with other non-Creative Suite applications? This is the reverse of the previous item. AS and VBS are likely going to be better suited although there will be situations where JS will work just fine.

4. Do you have a background in writing scripts? If so, one of the languages is likely more a appropriate choice for you.

5. What does everybody else do? There are a lot of people out there writing scripts for Photoshop. If you are interested in leveraging scripts that they've written or interacting with them on available online forums, choosing the same language might be important. A rough estimate would place JS at around 90% of the available 3rd party scripts and 85% of the forum traffic on various sites.

You may have noticed that this discussion mentioned nothing about language details. JS, AS, and VBS all have similar capabilities at the language level. The factors listed above will likely have more bearing on your choice of a scripting language than specific details about syntax.

A Simple Example

For a simple, but useful, example, let's look at a common requirement. We have an Action, 'Wood Frame #2' in Action set 'Wood Frame', that does what we need. However, it only works on landscape images and we have a mix of landscape and portrait ones. What we need to do is:

  • If the image is in portrait mode, rotate the image 90° clockwise, run the Action, and rotate the image back.
  • If the image is in landscape mode, just run the Action.

Here is what the JavaScript for this would look like:

            doc = activeDocument;
if (doc.height > doc.width) {
doc.rotateCanvas(90);
doAction('Wood Frame #2', 'Wood Frames');
doc.rotateCanvas(-90);
} else {
doAction('Wood Frame #2', 'Wood Frames');
}

Now, to explain this in detail.

  • The first line doc = activeDocument says that we want to use 'doc' to refer to the top-most document in Photoshop.
  • The line if (doc.height > doc.width) { says that if the height is greater than the width (portrait mode), execute the next three lines. If not, execute the line after the } else {.
  • The doc.rotateCanvas(90)/doc.rotateCanvas(-90) lines rotate the image clockwise and counter-clockwise respectively.
  • The doAction('Wood Frame #2', 'Wood Frames') lines do the work of running the Action from the Actions Palette.

The Photoshop JavaScript interpreter executes these lines of code in order and branches, if necessary, on the 'if' statement.

Now that we have this script, we can modify it to work with other Actions by simply changing the names of the Action and Action set in the script. To try this out, save this to a text file. Replace the Action with 'Image Effects – Blizzard' that comes with the PSCS2 distribution. If you then run the script (from File->Scripts->Browse), you'll see portrait images rotate before the Action is executed. As a result, the 'snow' is going in a different direction than it is in landscape images.

Whether this example is easy or not depends much on your technical background. If you've had any exposure to programming languages, it shouldn't be too hard to get a handle on what's going on in this script. If programming languages are something you're not familiar with, it may take a bit more work to get comfortable with some of the concepts. The References section has pointers to books and websites that provide good help in learning the JavaScript language.

A Complex Example

For a complex example, we will look at the Image Processor script that comes with Photoshop CS2. We will be looking at what scripting is capable of. A detailed look at the code is well beyond the scope of this article.
The Image Processor script is a kind of batch processor. With it, you can select source and destination folders, the file types and sizes to save, an optional Action to run, along with a few other properties. You can save your configuration for a batch run to a preferences file.

The script can be launched from File->Scripts->Image Processor. The script itself is located at PS Directory/Presets/Scripts/Image Processor.jsx.

When you run the Image Processor script, you are presented with this window:

This script obviously could not have been implemented by using the standard Batch and Action facilities of PSCS2.

  • Sections 1 and 2 look similar to panels in the standard Batch window, except for the 'Open first image' check box which facilitates work with sets of RAW images.
  • Batch does not have the capability to load and save batch run preferences.
  • In Section 3, you have the ability to choose file types and dimensions for a batch run. The best you can do without scripting is to record resize and saveAs steps for all three file types into an Action. Before running the batch you would have to manually change the Action to specify which resize and saveAs steps are active. This can be a very error prone exercise.
  • In Section 4, as in Section 3, these fields could all become steps in an Action but would require the same tedious modification of the Action before each batch run.

The programming power of the scripting language and Photoshop libraries makes it possible to write sophisticated scripts with a slick user interface and broad functionality.

In reality, most scripts that people write for Photoshop are not this complex and many have no user interface at all.

Resources

Books and Documentation

All of Adobe's documentation for scripting Photoshop can be downloaded from here. The Scripting Guide gives a good overview of how scripting fits into Photoshop. The Reference Guides are essential for finding out how to do anything at all with the scripting APIs. All of these PDFs are included with the PSCS2 distribution.

For a more introductory level book, I've heard good things about Beginning JavaScript (Wilton), but there are a great many other books on the market for getting started with JavaScript. Check your local bookstore.

For an online JavaScript reference www.croczilla.com is a fairly good site. There are others out there as well. Google can point you to them if croczilla doesn't work for you.

Tutorials

kirupa.com has probably the best (only) online tutorials for using JavaScript with Photoshop. Highly recommended.

User Forums

The Photoshop Scripting Forum hosted by Adobe provides access to some of the best and brightest Photoshop scripting minds in and outside of Adobe. The volume is around six to ten posts a day and the signal to noise ratio is good.

www.ps-scripts.com was setup last year by Andrew Hall and others as a compliment to the Adobe Forum. In addition to handling a bit more traffic than the Adobe Forum, ps-scripts also hosts scripts that have been uploaded by members of the community as well as provides a place for people to get basic support for those scripts.

If you are going to be doing any more than basic scripting with Photoshop, you'll find yourself visiting these two sites on a regular basis.

Scripts and Other Related Stuff

In addition to the scripts that come with PSCS2, you can visit Adobe Studio Exchange and find around sixty scripts that have been uploaded by other Photoshop scriptwriters. There's a lot of good stuff there. Scripts are also available at www.ps-scripts.com and other sites around the Internet.

One last site that needs mentioning is atncentral.com. They have the best online Actions tutorial as well as a nice collection of free Actions available for download. It's an excellent resource.

Conclusion

Hopefully this article helped to shed some light on the What, How, and Why of scripting in Photoshop. The Resources section contains an excellent set references to information that will prove helpful should you decide take advantage of the scripting capabilities in Photoshop.

About the Author

I have a long history in software engineering and photography. Scripting Photoshop has turned out to be excellent way to engage both of these passions. In addition to providing support to other scriptwriters on the Adobe Scripting Forum and ps-scripts.com, I also offer online consulting services for those in need of additional help.

You can contact xbytor here.

 
 
 
 
   

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