Nov 28, 2007

Smart filtering with the Lens blur filter


In Chapter 1 of my Adobe Photoshop CS3 for Photographers book, I provided a brief example of how one might apply the Lens Blur filter to a Smart Object in Photoshop CS3 and keep the background blur settings editable. However, it was pointed out to me just recently that the Lens Blur filter is actually disabled in CS3 when you seek to apply it to a Smart Object. This is one of those things that I failed to notice as I was finalizing the book and it seems that I am not the only author who got caught out by this late change to the program. Fortunately there is an easy remedy for accessing Lens Blur as a Smart Filter.

At first, disabling Lens Blur for Smart Objects seems like an odd thing to have done, because if you can use the Lens Blur to make a background go out of focus, you might well want the opportunity to re-edit those settings at a later date and work from an original, unblurred image – an ideal case for using Smart Filters. But then it was explained to me that one of the key features of the Lens Blur filter is its ability to reference an alpha channel and use this as a depth map to control the level of blurring across different parts of the image. This is indeed a useful feature, but it did have the potential to cause confusion when working with Smart Filters. Imagine you had applied the Lens Blur filter to a Smart Object layer and had referenced an alpha channel in the source document. If you were to later edit the alpha channel in the source document, the Smart Object layer would not register any change, no change that is until the next time you double-clicked to open the Lens Blur filter. Doing that would cause the smart filter to reference the alpha channel again and if the channel had been edited, you would only then see a new rendering of the Lens Blur filter. Figure 1 has a summary taken from chapter 1 of my book that shows the Lens Blur being used as a smart filter to blur the background in a photo.



Figure 1. In this example I opened a raw DNG image as a Smart Object and added a normal pixel layer of a backdrop image, which I then converted to become a Smart Object layer. I then added a layer mask to reveal the model on the layer below. Once a layer or group of layers have been converted to a Smart Object, one can then apply Smart Filters. Here, you can see how I applied a Lens Blur filter to the Smart Object and applied a gradient to the Smart Filters mask to reveal some of the unsharpened detail in the original pixel layer.

Now to be honest, if you are the type of person who is inclined to use the Lens Blur filter with depth maps, you are probably going to be OK coping with anomalies like this. The good news is that although the Lens Blur has been disabled to get around Photoshop’s inability to ‘paramertize’ the depth map settings, there is a simple way to override this behavior.

How to enable the Lens Blur filter
Help is at hand though in the form of a script that you will find inside your Adobe Photoshop CS3 application folder. Here are the instructions you need to enable all filters:


1. To enable Smart Filters for all plug-ins, go to the File ➯ Scripts menu in Photoshop CS3 and choose Browse…


2. This will open a system navigation window and from there you will want to use the following directory path: Adobe Photoshop CS3 folder/Scripting Guide/Sample Scripts/Javascript and select: EnableAllPluginsforSmartFilters.jsx (shown here is the Macintosh navigation window, but the PC directory path is exactly the same).

3. Once you have located the EnableAllPluginsforSmartFilters.jsx script, you can click Load or double-click to run it, which will then show the Script Alert dialog. If you wish to proceed, click ‘Yes’ and the Lens Blur including all other filters will now be accessible for use as smart filters. If you want to turn off this behavior, run through the same steps described here and click ‘No’ when the Script Alert dialog shows.

The benefits and pitfalls of enabling all filters
Now that you can see how simple it is to enable all filters, it is tempting to leave this as the new default. Which you can do of course, but it is worth bearing in mind that it is not just the Lens Blur you are gaining access to, but all filters that were previously unavailable for use as smart filters. However, unlike the Lens Blur, some of these do not fit in well with a smart filter workflow.

Basically, smart filters are intended for use with value based filters only: things like the Add Noise or Unsharp mask filter. They do not work well with filters that use brushes, such as ‘Liquify’. With ‘all filters enabled’ you can add Liquify as a smart filter, but the usefulness of doing so is restricted to turning an applied Liquify filter on or off. For example, you won’t be able to tweak the Liquify settings. If you double-click a Liquify filter in a filter stack it will cancel the current liquify settings and reopen the Liquify dialog with it reset to show no adjustments. This is not exactly what you would expect to happen here, but it does at least allow you to experiment with various liquify treatments and use the History palette to compare different liquified versions of an image. Likewise, if you adjust any filters in a smart filter stack, these too will force the Liquify dialog to reopen, with everything reset again.

Third-party plug-ins
With third-party plug-ins, the same rules apply, except you will find that those plug-ins that have been recently updated for CS3 should have an embedded smart filter marker that will automatically make them compatible with Smart Filters in CS3. If that is not the case, then enabling all filters in the way I describe here will help your get around such restrictions. But again, with the same provisos as before. Any filter you apply as a smart filter must be a ‘value based’ filter if it is to fit in successfully with a smart filter workflow.

My thanks to Uwe Steinmuelller for pointing out the ‘enable all filters’ script to me.

cover-versioncs3-low.jpg Adobe Photoshop CS3 for Photographers is published by Focal Press and can be purchased directly from Focal plus all the usual book publishing outlets.

This latest edition is 704 pages and comes with a DVD disk containing a CS3 Help Guide plus movie tutorials.

As a special perk for PhotoshopNews readers, Martin has made his Chapter 1: What’s New in Photoshop CS3 available for free download.

The 24 page PDF, outlines all the new features of Photoshop CS3 and Bridge 2, written from a user’s perspective. It offers an honest appraisal of what is on offer in Photoshop CS3.

Click here to download the PDF (4.05 MB)

You can also access a Photoshop News story on the latest Camera Raw 4.1 update and download a printable PDF supplement the book: Camera Raw 4.1 Update (2.5 MB)

2 Responses to “Smart filtering with the Lens blur filter”

  1. john4jack Says:

    Terrific. That is very helpful information. I especially appreciated the warnings regarding changing the default.

  2. sernak Says:

    Thank you , That is very helpful information

Leave a Reply

You must be logged in to post a comment.