In order to make the subject stand out a bit more prominently in the scene, it’s sometimes helpful to render the background less distracting.  There are several commonly used techniques for doing this.  In this section we’ll very briefly consider these.  Keep in mind that for many images you’ll only want to effect a very subtle change; not every image needs to have its background blurred into oblivion.  Start out with small changes and take your time evaluating the results visually.  I strongly recommend generating different versions of the image with different degrees of various adjustments.  Save these different versions as JPG’s and then move on to the next RAW image.  Later (preferably not the same day), you can come back and compare the alternative versions of an image and decide which looks best to you.  Don’t be surprised if your opinion changes on this matter from day to day.  Dealing with difficult decisions like this is simply part of the artistic process, and shouldn’t be rushed.  In time you may find that these types of decisions get easier as you become more confident in asserting your latent artistic preferences.
    The most common method for de-emphasizing the background is to blur it.  The reason this is so common among digital photographers is fairly obvious: images taken through an expensive prime lens with a shallow depth-of-field (DOF) often have a “buttery smooth” bokeh, which many photographers have come to covet and therefore wish to simulate via software.  Even photographers lucky enough to own an extremely expensive lens with good bokeh properties will sometimes want to blur the background in software, since not all photos will have a razor-thin DOF, and even those that do can still have distracting background elements intruding into the scene.  Just keep in mind that the popular obsession with smooth bokeh effects does not warrant making every one of your images look virtually identical via massive blurring of the background.  If every bird photographer blurred the background in every image, the effect would quickly become cliché (if it isn’t already).  Art shouldn’t be prescriptive: consider each photo as a chance to explore the possibilities for producing something both aesthetically pleasing and novel.
    There are two common ways of blurring the background in Photoshop.  The most obvious is to apply one of the Filter > Blur tools, of which there are many in Photoshop; the most useful of these, however, is typically the Gaussian Blur (though the Lens Blur can sometimes be effective as well).  In theory, all you need to do is select the background of the image (which is often easiest by selecting the bird and then using the Select > Inverse menu option to invert the selection) and then invoke the Gaussian Blur tool with an appropriate set of blurring parameters.  In practice, this almost always leads to rather obvious artifacts, and the main difficulty then becomes how to eliminate those artifacts—whether by covering them up with additional processing (such as cloning them out), or by using various selection tricks to prevent them from occurring in the first place.  We’ll explore some of the latter tricks first.
    The figure below introduces the photo we’ll use for our running example.  Although the background is already fairly blurred as shown here (despite having been acquired via a relatively small aperture of f/11), some “purists” might object to the distracting pattern of leaves in the background. 


    In the next figure (below) we show the same image after obliterating the background via aggressive use of the Gaussian Blur filter in Photoshop.  The result is an image that follows more closely the modern prescription for what is an acceptable bird photograph: namely, a detailed foreground and a “buttery smooth” background (or “bokeh”).  Whether this is more aesthetically (or artistically) pleasing to anyone is an entirely different matter, but for now let’s assume this is the effect you’d like to achieve with one or more of your photos.  We’ll now proceed to dissect some of the technical issues that can arise when employing aggressive blurring.


  The first task is obviously to select the background.  As already discussed, you can do this either directly (by selecting the background with the Quick Selection tool, for example), or by first selecting the foreground and then inverting the selection; another option, if the background is already of a fairly uniform color, is to use the Select > Color Range option.  In the figure below, the left pane shows the foreground after selection.  The right pane shows the result after inverting this selection (to select the background), duplicating the background to its own layer, and then applying a moderate Gaussian Blur effect.  Notce the slight brown haze around the periphery of the bird, particular around the bird’s head.  This is an extremely common—and often very frustrating—problem when attempting to blur an image’s background.



    The haze effect shown above occurred because some brown pixels (from the bird) were present in the otherwise green background layer prior to blurring; those handful of brown pixels seeded the blurring algorithm around the margin of the bird, resulting in the brown haze around the subject.  Preventing the haze therefore requires that the background layer be entirely devoid of any pixels from the foreground.  In this case, the brown pixels were present in the layer because the original selection of the bird (via the Quick Selection tool) wasn’t prefectly precise; after the selection was inverted, a contour of brown pixels remained in the background selection and were therefore copied to the background layer.
    There are several things you can do to prevent this from happening.  First, before inverting the selection, you can expand the selection by 1 or 2 pixels, to make sure that no part of the foreground lies beyond the selection boundary.  You can then zoom in and examine the selection boundary by eye to make sure that it contains the entire foreground; if it doesn’t, you can either expand the selection by another 1 or 2 pixels, or manually extend the selection in areas where it’s needed (perhaps using the Quick Selection tool or a paint brush in Quick Mask mode).  Once you’re sure the entire foreground is properly contained within the selection, you can then invert the selection and promote the selection to a layer.
    The next thing you’ll want to do is to lock the transparent pixels on the background layer (the new layer that you’ve just created from the selection).  This can be done by clicking the tiny checkerboard icon next to the “Lock” label at the top of the Layers palette, as depicted in the figure below.


Locking the transparent pixels will prevent the Gaussian Blur from extending into parts of the foreground.  If you fail to lock the transparent pixels and then apply the blur effect, you’ll likely notice that the periphery of the bird becomes somewhat blurry.  Locking the transparent pixels should prevent this.
    A more frustrating problem is how to deal with edge effects just within the boundary of the background layer.  When you expanded the foreground selection and then inverted it, you were effectively reducing the size of the background selection.  To the extent that the background selection may have originally intruded by a few pixels into the foreground, contracting the background selection in this way was productive.  But if you take this too far you’ll end up with a background selection that doesn’t contain all of the background pixels.  In the figure below we show a zoomed version of the blurred image from above.  Take note of the line of brighter green pixels along the bird’s breast and back.  You’ll also find some darker pixels that seem out of place around the bird’s legs and feet.

    These artifacts occurred because the background selection did not include those regions when it was promoted to a layer and then blurred.  The ideal solution would be to make sure that the selection was perfect before copying the area to its own layer, but in practice this can be both difficult and tedious.  A common fix (after the fact) is to use the clone tool with a small, hard-edged brush to overwrite the “shadow” or “halo” (after unlocking the transparent pixels) in the newly created background layer.  Although feathering the selection prior to creating the new layer can in some instances reduce the occurrence of such artifacts, doing so is rarely straightforward.  I personally prefer to use the clone tool (or a 1-pixel paintbrush for areas of uniform color) for such tasks; with practice, you can become surprisingly efficient at the use of these manual painting tools.  Unfortunately, if you later need to produce a version of the image at another resolution (e.g., for printing on large media), you’ll have to go through this painstaking process all over again.
    An alternative to the Gaussian Blur tool, for de-emphasizing the background in a more subtle way, is to apply noise reduction (via Filter > Noise > Reduce Noise).  Similar precautions such as expanding/contracting the selection and locking transparent pixels are required in this case as well, though the effect is typically more subtle than with a Gaussian Blur, and has the added benefit of reducing noise in the process while possibly retaining certain prominent details (via the Preserve Details slider).  I personally avoid using this technique, since it tends to leave telltale signs that other photographers quickly notice, though typical viewers probably wouldn’t find anything offensive about the result.  The Lens Blur filter is yet another alternative worth exploring.  Just keep in mind that a perfectly blurred background may be what you most crave right now, but might become less appetizing to your eyes as your tastes mature.  Remaining vigilant against cliché visual effects in digital image processing is an elusive but important virtue for any digital artist.
    Other methods for de-emphasizing the background include changes to the brightness and/or color (particularly saturation) of background pixels.  Depending on the properties of the foreground, you may want to either brighten or darken (or, alternatively, saturate or de-saturate) the background to achieve a more striking contrast between the foreground and background elements of the scene.  As already mentioned, you should try at first to err on the side of subtlety; a lack of subtlety is one of the first signs of amateur art.
    As demonstrated in section 11.5, another technique for reducing the complexity of the background is to clone out superfluous elements such as leaves or branches (or birdfeeders).  This can be a very laborious task in some cases, but can be extremely effective.  It does require a clone source, which needn’t necessarily come from the same image if you’ve got other images of the same scene (or similar scenes with consistent lighting).  When cloning from other photos, be very careful about the directionality of light; one of the strongest indicators of artificial cloning is inconsistent shadows—i.e., shadows indicating that the sun is both in the east and also in the west.
    Finally, as we’ll see in chapter 13, it’s possible to completely remove the image’s background and replace it with the background from another photo.  I’ve built up a small library of background images taken from highly uniform scenes with smooth (but not too smooth) bokeh, specifically for use as replacement backgrounds.  Replacing the entire background of an image is typically a very time-consuming task, so I personally only apply this technique for images that are already extremely promising.  My personal preference, however, is overwhelmingly to put in the extra effort in the field to get the right angle that will give me a nice background naturally, so that I don’t have to resort to tedious post-processing techniques to artificially improve the background of the image after the fact.  Nevertheless, I often hedge my bets by taking a few pure-background images when possible, to add to my archive of backdrops ready to be plugged in when needed during post-processing.