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Digital Photography Super Guide: How to Correct Your Photos
This is part of a new ongoing series on digital photography. Look for later installments covering various aspects of the topic, from choosing a camera and editing photos to printing them.
So you’ve taken some photos with your new digital camera, or even with your smartphone. What next? You could simply save, share, or print them as is, but a little effort with your photo software can turn washed out, dark, or poorly framed photos into something far more pleasing and impressive. In the last installment of PCMag.com’s Digital Photography Super Guide, we showed you how to effectively import and organize your pictures. This time, we’ll give you some ideas for how you can get them looking their best by applying image adjustments with photo software. Here we’ll discuss techniques that affect the whole image—things like cropping, brightness, contrast, color, sharpness, and noise reduction. In the next installment, we’ll move on to pixel-level editing tools for things like correcting red eye and blemishes, along with other nifty effects.
Just as we saw with importing and organizing, digital photography software comes in a few different levels. At the entry level are Web and mobile apps, such as Adobe Photoshop Express, Pixlr, FotoFlexer, and LunaPic. At the next level are free and OS-included photo editors, most prominently Windows Photo Gallery, Picasa, and the Mac’s iPhoto. All of these can perform the basic fixes—cropping, rotating, lighting, and color—and some will surprise you with more advanced features, such as red-eye reduction, retouching, and noise reduction. Of course, you get a lot more powerful advanced features when you move up to a software program such as Adobe Photoshop Elements, ACDSee, Corel PaintShop Pro , and Serif PhotoPlus.
Another level of photo applications, more skewed to pro and pro-sumer photographers are the “photo workflow” apps, with Adobe’s Lightroom the prime example. These products stress importing, organizing, outputting, and backing up your photos but they also include powerful image adjustment tools that handle all the functions just mentioned. Other products in this arena include CyberLink’s PhotoDirector , Apple’s Aperture, Corel AfterShot Pro and ACDSee Pro. Above this level, and pretty much in a class of its own is Adobe Photoshop CS6, which in addition to top-notch photo adjustment and enhancing tools, also adds 3D modeling, drawing, and endless image and even video-embellishing capabilities.
So what do you do with your photos to get them looking their best? In each of the next few sections, I’ll go through the major kinds of fixes that today’s photo software offers. Many, if not most, of these techniques are digital carryovers from the good old days of film photography—cropping, exposure, and even sharpening, for examples. One basic concept from those days is the negative, and many photo editing apps maintain this concept, by employing a “nondestructive” editing process. All this means is that your original photo file or a copy of it remains untouched no matter how many edits you make. Some apps simply make copies, while more sophisticated ones such as the workflow apps mentioned above, don’t touch the original, but instead maintain a database of your changes, which are used for display and exporting to shareable file types.
Another note about using digital negatives: If at all possible, say you’re shooting with a DSLR or higher-end mirrorless camera, it will definitely be to your advantage to shoot and import raw camera files, treating these as the negatives. Unfortunately, there isn’t just one raw file type, but rather each camera maker has its own standard. For example, Canon cameras produce .CR2 raw files, Nikons produce NEF files, and Sony cameras produce ARW files. And even within these filenames, each camera model’s raw files will have unique characteristics, so you have to make sure your software supports raw files from your particular model.
A raw file is considerably larger in size than the typical JPG format because it contains all of the information off your camera’s light sensor. Using raw camera files means that at the editing stage, you have a lot more potential for improvement, since the standard JPG, a compressed format, throws out data that may represent the very dark or very light parts of an image. I’ve shot light stucco walls that, in the JPG version of the photo I saw nothing but white, but when tweaking the same shot’s raw file, was able to bring out cracks and texture in the wall that had completely been lost in the JPG, for a far more convincing image.
Of course, if you’re not hardcore about getting the absolute optimal image, but simply want your photos looking as good as possible, there’s still plenty you can do without working with raw files. If your camera doesn’t let you get at the raw files, it’s still a good idea to shoot at its top resolution and quality level. We’ll start with the absolute basics, and then proceed to some more advanced adjustments.
Cropping and Straightening
Cropping is the most basic digital photo editing technique, and can potentially be the most effective and powerful. It lets you cut out the unimportant parts of a photo and zoom in on what is important. Shooting at the top resolution, as just mentioned, will enable the most leeway when it comes to cropping. A higher resolution image will stay clear as you enlarge it on the screen to discard unwanted parts, while a photo with smaller pixel dimensions will be unusable except in a completely uncropped state. In addition to simply zeroing in on the important part of a photo, cropping can give the photo pleasing proportions, including the aesthetically ideal “golden rectangle” or the classic square, made so popular by Instagram. Or you could just crop to fit a computer screen perfectly. Most importantly, cropping gives you a chance to recompose the photo after the fact. For example, you can have your photo obey the rule of thirds by placing the central point of interest (say an eye) off center. Or you can center a subject that wasn’t perfectly centered.
Related to cropping is straightening. How often have you taken a photo where the background buildings are off-kilter, producing a bit of vertigo in the beholder? Usually a photo app’s crop tool will offer the ability to straighten out the image, with rules overlaid to help you align the horizon or a building roof. Some apps, such as Windows Photo Gallery, even can attempt to find the horizon to straighten the photo automatically. For a really basic form of straightening, make sure you’re not one of those people who sends photos that make people crane their necks to the side: rotate any photos that you shot sideways!
Lighting—Brightness, Contrast, and More
There’s nothing like getting the exposure right “in camera,” but photo software certainly can save some picture that you may have thought were unusable due to over or under exposure. The brightness slider in just about any photo app will let you correct a completely over or underexposed photo. Don’t expect the image to look as good as it would if you shot with the right exposure setting in the first place, but at least you’ll be able to decipher what you were taking a picture of.
A good idea for getting started is to use your software’s “auto exposure” button. Though I’ve found that none of these automatic lighting correctors works well on every photo you throw at it, they can often provide a good starting point for your further adjustments. And pros, don’t snigger; a product manager of Photoshop told me that, even though pro photographers say they never use the “auto” button, feedback data shows that a third of them do in fact use it.
The case may just be that part of the photo (usually a person) is too dark compared with a bright sky behind. The better photo software has an excellent adjustment to handle just this situation. Most apps call this adjustment “shadows,” while others call it “fill light.” It’s usually in the form of a slider that brightens up just the dim areas. This is important, because brightening the whole image evenly would mean that that sky becomes a featureless white. The converse “highlights” control in good software is for getting back detail from too-bright parts of the photo without turning dark areas black.
Maybe your picture is just washed out or too dim. Any photo app will let you make it more compelling by simply bumping up the contrast with a slider. Increasing contrast simply gives you a greater range of shades, bumping up the highlights and darkening the darks. Of course, you may want to go in the other direction, giving a photo a more dreamy, impressionistic look.
For really advanced manipulation of different brightness levels in a photo, advanced apps let you manipulate histograms and tone curves. These tools graphically represent the whole range of shade in an image, and selectively bump them up or tone them down. A histogram is an area graph of the whole image contents from the darkest to lightest tones. Sometimes you can perfect an image simply by moving adjusters at the sides and middle of a histogram, for example, cutting out all the overexposed bits. A curve control is a line graph that lets you manipulate the output brightness for a given input brightness. Higher-end photo apps offer this kind of adjustment, which can be far more effective than simple brightness, contrast, or even shadow adjustments.
Another more advanced way to correct lighting is to use a local “brush.” This is equivalent to the old darkroom techniques of “dodging” and “burning.” The higher end apps let you brush brightness or contrast right on to specific parts of a photo, leaving the rest of it untouched. This gets into the area of creative editing, as opposed to simply adjusting the photo for the most realistic, clear look.
Reproducing color correctly as you saw the scene before you when you were snapping pics means getting the “white balance” right. This means that the white in your photo will acutally show up as white, but different light sources—incandescent, sun, fluorescent—produce white objects of different hues. Of course, all the other colors will be wrong, too, if you, say shoot a fluorescent-lit scene using the daylight setting. Get the white balance perfect, you’ll have to calibrate your camera WB setting with a neutral gray card. But fear not: Most cameras today do a pretty good job with their AWB—auto white balance setting. If you capture raw camera files, as recommended above, you can very powerfully adjust the white balance on your computer later as though you were changing the setting at shoot time. Even if you didn’t shoot in raw, you can usually correct the white balance by either picking the correct light source or trying the app’s AWB button.
Our final color related correction is chromatic aberration. The name sounds quite impressive, but we’ve all seen it, and it’s not pretty. There was recently a scandal revolving around the iPhone 5: Its camera was producing purple fringing—a form of chromatic aberration (CA). Chromatic aberration is an artifact of lens physics in which neighboring colors are distorted, usually seen in the edges of dark objects against light background. It’s most evident in the edges of wide angle shots. Unfortunately, most photo apps struggle with chromatic aberration, even when they have tools for its correction.
Chromatic aberration correction is only found in high-end apps, and the adjustments in most simply replace or change the offending color of the fringes, and can certainly reduce the color distortion. But in my experience, only three apps can reliably remove it: DxO Optics, Lightroom 4, and Photoshop—the last two actually use the same underlying mechanism. Both of these apps match the fix to the exact lens and camera body you used, and both pretty much eliminate the distortion without all the painstaking tweaking required by other apps. On the plus side: with today’s cameras, you’ll usually only see chromatic aberration in photos enlarged to 100 percent size and in the edges of the photo.
The sharpness of a digital photo depends on your camera’s sensor, lens, and processor. Also called “detail,” sharpening is a key aspect of digital photos, and any image you see onscreen has undergone sharpening to some degree by the camera itself, before you even see it on a screen. Photo apps from entry-level to pro usually offer sharpness or detail setting with a slider. Be careful with this, though, an overly sharp image will look less natural than one with a little bit of blur, and can actually increase the undesired effects of image noise (see next section).
Using this adjustment will never correct problems that result from shaking the camera or shot well out of focus. But it can add crispness to overly soft-looking pictures. It does this by increasing the contrast at objects edges in the photo, where a light area meets dark one. More advanced software lets you adjust the size of edges this effect acts on, and the threshold of brightness difference for what constitutes an edge. Sharpening is yet another photo correction that works much better with raw camera files than with JPGs.
If you want to print your photos, another round of sharpening is usually required, and good software at every level—even Windows Photo Gallery—can perform this round of sharpening automatically. Of course, more advanced digital photographers will want to tweak output sharpening. Photos reduced for email and Web use also can look better with sharpening, since the resizing can soften or add moiré, a distortion pattern similar the one that appears when you look through two separate screens.
We’ve all seen those little dots on dark areas of photos that we know should be smooth. This noise is a result of electronic signal interference, which is unavoidable in any electronic transmission. Noise is the digital equivalent of the film camera’s grain, and as such, can sometimes be used as a desirable artistic effect. But usually you’ll just want to eliminate noise from your photos, and software at all levels lets you do this. But maybe even more than CA, noise reduction is handled with greatly varying success by different apps. Apple iPhoto and Windows Photo Gallery offer noise reduction, though Picasa doesn’t.
Higher-end photo software, as you’d expect, offers more powerful control over image noise. In fact, the leading tool in this space—Noise Ninja—isn’t built into Photoshop or Aperture, but is available as a plug-in for those apps. The higher-end tools go beyond just offering a single de-noise slider like that in iPhoto or Windows Photo Gallery. They let you differentiate between luminance (light and dark) versus color noise and correct the detail (the threshold of what’s considered noise) and strength of each type. Reducing noise can result in blurring and color bleeding, so use it judiciously.
Next time, we’ll go beyond overall image corrections and move toward enhancing your photos with pixel-level editing and adding special effects, including red eye correction, retouching, slimming, teeth whitening, high-dynamic-range, vignetting, selective focus, and even adding removing people with content aware tools.
By Michael Muchmore, PCMag