Adobe Photoshop CS5 for Photographers - Martin Evening [233]
Depth of field effects
With the Lens Blur filter you can also use a mask channel to define the areas where you wish to selectively apply the Lens Blur. This allows you to create shallow depth of field effects, such as in the example shown on the right. Basically, you can use a simple gradient (or a more complex mask even) to define the areas that you wish to remain sharp and those that you want to appear out of focus. You can then load the channel mask as a Depth Map in the Lens Blur dialog and use the Blur Focal Distance slider to determine which areas remain sharpest.
1.
In this example, I created a linear gradient mask channel called Alpha 1, where the gradient went from white to black. I then loaded the Alpha 1 channel in the Lens Blur filter dialog to use this as a depth map. With the Alpha 1 channel selected, I could adjust the Blur Focal Distance slider (circled) to determine the point where I wanted the image to remain sharp and not have the Lens Blur affect this portion of the image.
2.
Another way to use a depth map is to click in the preview area to set the point where the image should be sharpest. Basically, the degree of lens blur is linked to the gray values in the Depth Map source channel.
Applying Lens Blur to a composite image
Here is a short step-by-step example which shows how I applied the Lens Blur filter to make the background in this composite image appear out of focus. You will notice that I applied the Lens Blur filter here as a Smart Object (see pages 546 and 550–555).
1.
In the following steps I took two separate photographs and created a mask for the outline of my wife in the picture on the left, and placed this as a new layer above a photograph of the Chicago skyline.
2.
As you can see, when the two images were merged, the buildings in the background looked too sharp. So in preparation for applying the Lens Blur filter, I selected the Chicago skyline layer, went to the Filter menu and chose ‘Convert for Smart Filters’. This was essentially the same thing as choosing Layer Smart Objects Convert to Smart Object. Do read the side panel notes on enabling Smart Objects to work with the Lens Blur filter (page 546), before proceeding to the next step.
3.
To make the background appear out of focus, I selected the Chicago skyline, Smart Filter layer and chose Filter Blur Lens Blur. Here, I adjusted the Specular Highlights Threshold setting, bringing it down just enough until the highlights started to bloom. I then adjusted the Specular Highlights Brightness setting to create the desired amount of lens flare. The Iris Radius slider was used to control the width of the blur (the effect of this adjustment was particularly noticeable in the specular highlights).
4.
This shows the finished result, where you can see the Lens Blur Smart Filter attached to the Smart Object layer. The advantage of this approach is that I retained the ability to re-edit the Lens Blur filter settings and vary the background layer focus.
Third-party plug-ins
With third-party plug-ins, you will find that those plug-ins that have been recently updated for Photoshop will have the embedded ‘Smart Filter’ marker that automatically makes them compatible with Smart Filters in Photoshop. If that isn't the case, then enabling all filters (as described on page 546) will help you get around such restrictions, but with the proviso that 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. Some Photoshop filters, as well as advanced third-party filters, require the use of things like external channels or texture maps in order to work correctly. Since this information can't be stored safely within the Smart Object itself, this can prevent a Smart Filter from working reliably.
Smart Filters