11.6 Sharpening

Probably the most under-appreciated challenge of digital postprocessing of bird images is that of sharpening.  Recall that because most DSLR cameras employ an anti-aliasing filter in front of the imaging sensor, which has a dispersive effect on the pixel information in the raw image, some degree of artificial sharpening in postprocess is almost always necessary in order to reclaim the crispness of the original scene.
    When I first started digitally processing bird images, I never expected the degree of difficulty I would eventually face in trying to find the ideal sharpening parameters for my images.  One of the problems is that my tastes regarding the ideal amount of sharpening have changed over time.  At first I liked seeing all of my images with maximal sharpness—probably because I had become so frustrated with the softness imparted by the optically inferior lens I was using at the time.  In time I became aware that many of my postprocessed images appeared over-sharpened—a quality that those with experience in digital imaging can identify almost immediately, though to novices it’s not always immediately apparent.  Over-sharpened images, more than anything else, carry the stigma of being the product of an amateur—or, worse yet, someone lacking any semblance of artistic talent or taste.
    As a result, I stopped sharpening my images so aggressively, and in some cases I over-compensated by leaving my images too soft.  I’ve now realized that there is a very, very delicate balance between artificial sharpening and natural softness that produces the most aesthetic images—at least from my perspective.  Sharpness, like any other image aspect, is to a large degree a subjective quality.  For that reason, there are no hard-and-fast rules that can be followed to always consistently produce the ideal results.  As with any art form, you need to learn to listen to the intuition embedded in your visual cortex and other primitive brain centers to aid your rational decision-making during postprocessing.  In this section we’ll consider a number of issues and general rules-of-thumb that you can use as an initial set of mental crutches as you refine your sharpening technique.
    First, let’s consider the tools at your disposal.  In Photoshop, there are several distinct tools that can be used to artificially increase the sharpness of an image.  The one I recommend most strongly is the Sharpening pane in Adobe Camera Raw (ACR), which is depicted in the figure below.

Fig. 11.6.1: The Sharpening pane of Adobe Camera Raw.

The advantage of sharpening in Adobe Camera Raw (ACR) is that the sharpening algorithm used by the software has access to the largest amount of information, since it is applied directly to the RAW file during conversion to Photoshop’s internal representation.  Keep in mind, however, that the degree of advantage that you gain from performing sharpening during RAW conversion (versus doing it later, after conversion, in Photoshop proper) may very well be camera-dependent, since the process of RAW conversion is necessarily tailored to the different file formats of different camera vendors.  For my Canon EOS 1D Mark III camera, I find that the sharpening effect that I can achieve in ACR is far superior to what I can achieve later in Photoshop proper (with default ACR settings), so I try to perform the bulk of my sharpening in ACR, though I always apply a bit of additional sharpening later in Photoshop proper, after conversion and resizing of the image for the specific distribution medium (e.g., web page, photographic paper, or canvas).
    In the above figure you can see that the version of ACR that I currently use provides four sliders: Amount, Radius, Detail, and Masking.  I always leave Radius at 0.5 and Masking at 0, and then try to find the ideal settings for Amount and Detail.  Note that in some versions of ACR, the effect of these sharpening sliders is only apparent when viewing the image at 100% zoom.  In my experience, the Detail slider tends to affect the finest details in the image, and should be set most aggressively, while the Sharpening slider needs to be set more conservatively to avoid artifacts due to over-sharpening.
    After setting the sharpening parameters (and any others in ACR), I then convert the image from RAW and view it in Photoshop proper.  Often I’ll find that the image, after conversion from RAW, doesn’t exhibit the ideal amount of sharpening, and I then need to close the file and re-open it in ACR so that I can change the sharpening parameters and re-convert from RAW.  Though this is an awkward and inconvenient process, I generally find that it’s more than worthwhile, since the sharpening tools in Photoshop proper often can’t reproduce the exact sharpening effect that those in ACR can.
    Once I’ve got the image into Photoshop proper and I’m more-or-less satisfied with the sharpness of the full-resolution image, I then reduce the resolution as desired (via the Image Size window, which I have tied to the Cmd-I key combination on my computer) and adjust the sharpness of the reduced image using the Unsharp Mask tool of Photoshop, which is depicated below.

Fig. 11.6.2: The unshsarp mask in Photoshop.

The Unsharp Mask is by far the most popular sharpening method in Photoshop.  As you can see above, the tool provides a tiny preview of the image, though with the Preview check-box checked, the entire image will also act as a preview (though you should make sure that the image is zoomed to 100% before using the image preview to assess the effect of sharpening). 
    The three parameters of the Unsharp Mask are Amount, Radius, and Threshold.  For the vast majority of cases, I set the Threshold to 0 and the Radius to 0.15, and then adjust the Amount slider until the image looks best to my eye.  For my current version of Photoshop (version CS3), 0.15 is the smallest radius that has any effect, so it allows me to attend to the smallest possible details in the image.  In some cases I do find that 0.15 results in too many image artifacts (primarily whitish pixels appearing in the busiest parts of the bird’s plumage), and will then set it instead to 2.0.  On rare occasions I’ll use a radius of 1.0 in conjunction with an extremely small Amount setting; this tends to improve the overall perception of clarity in the bird without over-sharpening the fine details or introducing halos and other artifacts associated with over-sharpening.  It’s worth experimenting with the Threshold slider in cases in which you keep getting artifacts whenever you get close to the amount of sharpening that you think is required.  The Threshold parameter can sometimes eliminate or reduce those artifacts without affecting the resulting clarity achieved by the sharpening.  But for the vast majority of post-conversion sharpening that I do, the Threshold is set to 0 and the Radius to 0.15, and I just painstakingly vary the Amount slider until the image (at 100% zoom) looks good to my eye.
   Though the Unsharp Mask is the most popular sharpening method for serious Photoshop users, there is one other tool that some people swear by: Smart Sharpen.  This tool is considerably more sophisticated than the Unsharp Mask.  First, it allows you to set separate sharpening parameters for shadow and highlight regions of the image.  Second, it automatically applies a post-sharpening blur to help reduce artifacts introduced by the sharpening procedure.

Fig. 11.6.3: The Smart Sharpen tool in Photoshop.

The Smart Sharpen tool is highly flexible and undoubtedly very powerful.  I’ve personally avoided using it because I find that the preview that is rendered in real-time doesn’t always match the way the image looks after I press the OK button and commit the changes.  I instead find the combination of sharpening in ACR and fine-tuning later in Photoshop via the Unsharp Mask (after changing image resolution via the Image Size tool) to provide all the flexibility I need.  The real challenge is finding the ideal parameter settings for these respective tools, so as to produce the most aesthetically pleasing bird images.  The latter goal is what we’ll concentrate on for the remainder of this section.
    First, we need to note several things.  The issue of monitor-dependence is one of the most important—and most unfortunate.  After upgrading my Apple laptop to a newer model of the same line, I noticed that many of my bird photos that looked tack-sharp on my older laptop no longer looked so nice on the newer machine.  Different computer monitors can differ fairly substantially not only in the pixel pitch (the number of pixels per millimeter—or, stated differently, the size of the individual pixels, in micrometers), but also in their color fidelity and contrast ratio.  As computer manufacturers continue to make improvements to their hardware over the years, newer monitors will inevitably become better and better.  Unfortunately, this doesn’t necessarily mean that your images, postprocessed on an older monitor, will look better on newer monitors.  Over time you’ll become highly proficient at precisely optimizing your images so as to look virtually perfect on your particular computer’s monitor.  Just keep in mind that differences in rendering technologies will result in your image looking somewhat different (whether better or worse) on other peoples’ monitors.  This is a very frustrating aspect of digital imaging, but one that does not seem to have any practical solution at present.  (See section 16.2.4 for a discussion of the related issue of gamma differences between monitors).  Note also that sharpening is highly medium dependent, so don’t assume that the ideal sharpening for internet distribution of your images will also serve as the optimal parameterization for printing (see Chapter 14).
    Second, it’s important to note at the outset that the ideal sharpening amount can be highly variable across the image.  In particular, you’ll typically want to sharpen the eye and beak separately from the rest of the bird, since the eye and beak are the two most psychologically salient features to human observers of birds.  I generally sharpen the beak more than any other part of the bird, often setting the Amount slider to 500% in the Unsharp Mask.  The eye I typically sharpen less than the beak, but more than any other part of the bird.  In both cases (eye and beak) I generally use a radius of 0.15.  Sharpening of the eye and beak is usually very straightforward.  The difficulty generally arises when trying to find the ideal amount of sharpening of the bird’s plumage.  This will, therefore, be the focus of the rest of this section.  We'll proceed largely by anecdotal illustration, since this is a highly subjective issue and will necessarily vary in subtle ways from image to image.
    Let’s start by considering the example illustrated below.  For this flycatcher, the eye and beak appear suitably sharp (the beak could be slightly sharper, but it’s at least acceptably sharp).  What remains is to assess the sharpness of the bird’s plumage.

Fig. 11.6.4: Flycatcher with a fly.

For this particular example, the overall bird appears suitably sharpened on my monitor—though on yours it may appear over- or under-sharpened, depending on your monitor’s pixel characteristics.  On my monitor I can just start to discern the individual feather barbs making up the bird’s plumage, though none of those fine-scaled biological features show any obvious image artifacts here (on my screen, at least).  The white parts of the bird’s ventral side show sufficient detail in all areas, indicating that little or no over-exposure has occurred.  The top of the bird’s head exhibits some feather glare, possibly due to flash, and there are a few sharpening artifacts—apparent as whitish pixels that stand out from the rest.  Take special note also of the wing feathers.  They vary from sharp to soft, largely as dictated by the depth-of-field (DOF) induced by the configuration of the optical system (e.g., the aperture and distance to subject), and are therefore somewhat natural.  The fly in the bird’s mouth could, in my opinion, be sharper, as could the bird’s feet.
    Continuing in the vein of instruction-by-example, let’s consider the bay-breasted warbler shown below.  The beak appears suitably sharp, as does the eye.  The rest of the head is less sharp.  The bird’s upper back appears quite sharp, and in my opinion shows very few (if any) sharpening artifacts.  The flight feathers on the left wing show a region of very nice sharpness, though the DOF is very shallow here, so the tips of those feathers are suitably blurred.  The bird’s right flank looks a bit unnatural to me, though the number of sharpening artifacts (i.e., unnaturally whitish pixels) in this region isn’t terribly large.  The bright part of the bird’s dorsal neck (the thin slice of direct sunlight striking the bird from behind) does appear over-sharpened, showing that over-sharpening can be exposure-dependent.

Fig. 11.6.5: Bay-breasted warbler.

    For the next example, a Prothonotary warbler, the sharpest elements are the beak and the toes.  The DOF is again shallow, with the in-focus area including only the bird’s head and feet, and the perching substrate.  Keep in mind that DOF is a natural phenomenon that viewers can intuitively relate to, so don’t try to unnaturally sharpen parts of the bird falling outside the shallow focus area.  In the example below I think the beak is adequately sharpened, and the eye is probably adequately sharpened as well, though the rest of the bird’s head (particularly the throat region) could be sharpened slightly more.  In this case the wing coverts could probably have been sharpened a tiny bit more, since they’re obviously a high-contrast feature on this bird.  Note that sharpening of the intense yellow regions of this bird can be difficult, since sharpening filters will tend to produce artifacts (isolated bright pixels) in these types of cases.  Don’t hesitate to select even the smallest regions of the bird for differential sharpening.  Also, recall (from section 11.2) that the Highlights filter can in many cases be used to bring out subtle details in bright plumage areas; the Unsharp Mask isn't the only tool at your disposal in this regard.

Fig. 11.6.6: Prothonotary warbler.

    The image blow is of another Prothonotary warbler.  In this case, a bit a over-sharpening is apparent, primarily in the back, mid-wing, and flank regions of the bird.  To me, the head and beak look nearly perfect, with no evidence of over-sharpening.  The tail looks likewise quite acceptable as-is.  Notice in this example that the wing comprises a number of different regions, each with different sharpening needs, due to their differing positions relative to the focus plane.  The nearer parts of the wing look perfect to me, the middle portions somewhat blurry, and the distal portions again suitably sharpened. 

Fig. 11.6.7: Prothonotary warbler.

    For the Palm Warbler image below, we’re again faced with an exceptionally shallow DOF, comprising less than an inch of perfectly in-focus area.  The beak falls somewhat outside this area, and is consequently less-than-perfectly sharp.  The sharpest regions are the throat, the cheek, the dorsal portion of the head and nape, and the upper chest.  The only parts that strike me as slightly over-sharpened are the throat (directly beneath the beak) and the nape, which exhibits some very, very slight artifacts (isolated whitish pixels).  The top of the head could use some more sharpening, in my opinion, possibly with a large radius and small amount.  Otherwise, the lack of sharpness in the regions of the bird outside the focus area seem appropriate to me, given the shallow DOF.

Fig. 11.6.8: Palm warbler.

    The next example again features a palm warbler.  In this case the eye and beak look slightly soft to me, as does the rusty cap, while the bird’s chest, back, belly, and wing look well-sharpened on my monitor.  To sharpen up the eye and beak in this example, I’d simply use the Quick Select tool to select those regions and then open the Unsharp Mask while those regions are still selected.  When there is an active selection in the image, the Unsharp Mask affects only those selected regions (just as with any other filter in Photoshop). 

Fig. 11.6.9: Palm warbler.

    For the next example (below) we have a chestnut-sided warbler.  On my screen the overall sharpness looks fine, though the beak could use a bit more sharpening.  Notice that the white underside of the bird has a large amount of detail.  Much of what you’re seeing in that white region is actually an artifact of agressive sharpening, in combination with micro-contrast induced by flash (see section 7.1).  The local aggregations of pure white pixels would, in a non-white part of the bird, create an impression of over-sharpening, but in the pure white plumage it can sometimes help to over-sharpen in order to emphasize details that would otherwise go unnoticed in a sea of almost pure white.

Fig. 11.6.10: Chestnut-sided warbler

    Our next example features a golden-winged warbler (below).  The only thing that appears under-sharpened on my monitor is this bird’s eye.  The near-white underside of the bird is, in my opinion, tastefully over-sharpened—meaning that over-sharpening of this near-white area has brought out details that would be otherwise difficult to see.  In contrast, the bird’s back is just starting to show some moire artifacts due to sharpening, and these generally aren’t aesthetically pleasing.  In this case, on my monitor, the effect is quite tolerable, but if it were sharpened just a tad more it would probably look offensive to my eyes.

Fig. 11.6.11: Golden-winged warbler.

     For the Baltimore oriole below, the overall sharpeness looks good on my monitor.  The beak and head feathers are well-defined, though the beak could possibly use just a tad more sharpening.  Beaks can take quite a lot of sharpening without looking over-done, certainly more so than feathers.  Keep in mind that all of these images will likely be rendered at a different pixel pitch on your monitor (unless you happen to have exactly the same laptop model I’m using), and your assessment of what looks like an ideal amount of sharpening will likely differ.  This is the curse of media-dependent image qualities (of which sharpness is just one).

Fig. 11.6.12: Baltimore Oriole.

    Continuing on to the next example image, the female yellow warbler below looks slightly soft to me in her eye, while some moire patterning in the bird’s back feathers suggests over-sharpening.  Moire is, of course, a natural phenomenon that you can perceive even when viewing the bird with your naked eyes, and is especially prevalent in certain types of feather patterns.  The difficulty is to try to both avoid creating unnatural moire patterns and to also avoid exacerbating natural moire patterns into what many viewers will perceive as sharpening artifacts (whether they are or not).  This simply requires experimentation with different sharpening levels as applied to the specific part of the bird that is most moire-prone.

Fig. 11.6.13: Female yellow warbler.

     The next example (below) again illustrates the value of aggressive sharpening in white plumage.  Though this bird’s underside is arguably not over-sharpened, a bit of over-sharpening might actually help to further emphasize the detail present in that vast white region.  Regarding the rest of the bird, I find the lower wing feathers to be appropriately sharp, the upper wing feathers to be appropriately soft, and the face (including the eye) to also be appropriately soft.  The eye, which appears remarkably three-dimensional in this image, could probably bear additional sharpening, but in this case I think it has enough definition to stand as-is.  Though the beak could be sharper, its slight softness matches that of the rest of the face.  Remember that modern viewers are aware (even if subconsiously) of the issue of depth-of-field (DOF), so when your DOF is razor-thin, some softness in the out-of-DOF regions are not only acceptable but indeed expected.  To the extent that you may be striving for a true photographic look (rather than an artificial, painted effect), your sharpening strategy should respect any apparent DOF in the image.  For more abstract works, however, such constraints can be largely set aside.

Fig. 11.6.14: Tree swallow.

     The vireo image below illustrates the value of softness (as opposed to sharpness) for certain images.  To my mind, vireos appear naturally soft, and for that reason I’ve left much of the bird under-sharpened (especially parts of the bird below the head).  A slight suggestion of moire is still present, however, in the visible portion of the bird’s back and in its cap.  The beak and eye appear appropriately soft for this image.  Over-sharpening of the white underside has not been applied, in agreement with the overall soft theme of this image.  The bird’s feet and the branch it’s perched on could use more sharpening, however.

Fig. 11.6.15: Vireo.

     In contrast to the image above, the red-eyed vireo in the image below exhibits some obvious sharpening artifacts (as well as a bit of over-flash in the face and neck).  Moire is clearly present in the cap.  The eye is quite sharp, though the beak unfortunately falls somewhat out of the DOF and therefore appears soft.  Some moire is apparent in the bird’s back and in the wing coverts.  A bit of over-sharpening is also apparent in the part of the bird’s head starting at the right cheek and extending around toward the back of the head.  Though the perfect sharpness of the eye may appear a bit unnatural if you look too closely at it, the extreme sharpness helps to focus the viewer’s attention on the most salient aspect of the creature, and to establish the center of the DOF.

Fig. 11.6.16: Red-eyed Vireo.

     For the next vireo (below), we’ve again opted for an overall soft look, though a number of sharpening artifacts are nonetheless present.  The white pixels in the bird’s belly are just slightly over-sharpened: they create the impression of excessive flash in that part of the bird.  The flight feathers appear appropriately soft on my monitor, and the primary and secondary coverts seem slightly soft, but consistent with the overall theme of the image.  Moire is clearly present, however, in the bird’s back, and some over-sharpening is apparent in the bird’s cap.  The beak is appropriately soft for the image.  The tail looks a bit too soft to me.

Fig. 11.6.17: Red-eyed Vireo.

     As one final example, the chestnust-sided warbler below combines tasteful softness in the wings with moderate over-sharpening in the white ventral regions to create an image featuring a range of textures.  I’d personally prefer to see the white ventral region slightly less over-sharpened. 

Fig. 11.6.18: Chestnut-sided warbler.

    One trick that may help you in finding the right sharpening parameters is to first duplicate the bird layer, apply fairly aggressive sharpening to that duplicate layer, and then decrease the layer opacity in the Layers panel.  Sometimes exploring different opacities of the sharpened version of the layer makes it easier to make up your mind about how much sharpening you want.  In some cases you may also be able to achieve an effect that direct sharpening can’t give you, since sharpening artifacts can be softened by the blending of the sharpened layer with the unsharpened layer.  I find that this approach often seems to make the effect of the sharpening more subtle, so that the bird looks sharp without looking artificially sharpened.  A related technique is to subject the duplicated layer to a high pass filter (Filter > Other > High Pass) with a radius of 0.5, and then to set the layer's blend mode to Overlay or Soft/Hard/Vivid Light, with an appropriate opacity.
    Occasionally you’ll find that no matter what sharpening parameters you try, the final product never looks right to you, even when the original photo lacked any obvious motion blur or focus problems.  One thing you can try is to apply the sharpening and then to reduce contrast slightly via the Brightness/Contrast tool.  Though sharpening works by increasing local contrast, it sometimes results in an apparent increase of contrast at a courser scale, which the Brightness/Contrast tool can rectify by dialing in -5 or -10 for the Contrast slider.  In rare cases you might also find that adjusting saturation a tiny bit can alter your perception of the effect of a previously-applied sharpening pass.  Remember also that noise reduction and sharpening (in either order) can interact to create an effect that looks better or worse, depending on the image and the chosen sharpening or denoising parameters.
    Hopefully, the above examples and anecdotal commentary will provide you with some ideas for analyzing your own images and the effects that various sharpening parameters have on them.  Over-sharpening artifacts can be difficult to identify for novices, so keep an eye out for moire patterns and unnatural white or black pixels that result from the sharpening algorithm’s attempt to increase local contrast in feather details.  Over-sharpening in white plumages is sometimes acceptable and even desirable, though it can be over-done.  And remember that softness (i.e., lack of sharpness) can sometimes reinforce thematic aspects of an image.  Both sharpness and softness are tools that you, as an artist, can use to convey your feelings and impressions about a scene and its subject.  And know with certainty that your own opinions and preferences will naturally evolve as you gain more experience with digital post-processing of bird images.  Learning to accept that natural evolution of thought is an essential part of the tao of digital bird photography.