Reduce Digital Noise in Your Photos

There is little doubt that even run-of-the-mill digital cameras take better pictures than the best point-and-shoot film cameras did 30 years ago. Almost everything is better: The optics, the exposure controls, even the resolution. All the potential problems haven't been solved, though. Both digital and film photos can turn out grainy and unattractive. In digital photography, this is called noise; read "Eliminate Noise From Your Photos" for more details.

Back in the days of film, something called grain added a coarse texture to photos. These days, digital noise has pretty much the same effect. Your shooting conditions can contribute to digital noise (see "Use ISO to Take Low-Light Photos."). This week, let's explore what noise is all about and how to minimize it in your photos.

What Causes Noise

People often compare digital noise to old-fashioned film grain, and for good reason. Not only do they look somewhat similar, but they are caused by similar factors.

First and foremost, digital noise is accentuated by high ISO levels. ISO is a measure of your camera sensor's (or film's) sensitivity to light. Most digital cameras let you increase the ISO level so you can take photos in low-light situations. There's always some noise in your photos, even at your camera's lowest ISO, but the higher you crank the camera's ISO dial, the more noise results. You can see what this looks in this photo of a wolf that I snapped at an unfortunate ISO 1600.

Long exposures are also breeding grounds for noise. The longer the exposure, the hotter your camera sensor gets--and all that heat contributes to digital noise in the final image. That's rarely a problem in daylight photography, but long exposures at night can be filled with noise. This detail from a night photo I took with a point-and-shoot camera shows just how noisy things can get when the shutter left open for several seconds.

Finally, one other important contributor to noise is underexposure. You'll almost always see more digital noise in darker areas of photos and in images that are underexposed. That noise gets more noticeable as you "enhance" an underexposed photo, so it's important to get the exposure right when you take the picture.

If you ever take a dramatically underexposed image and brighten it in your photo editing program, you will probably notice that the resulting image is noisier than a Quiet Riot concert, as in this photo that was brightened in Adobe Photoshop Elements.

Avoiding Noise

So now that you know what causes noise, how do you avoid it?

Well, remember that one of your jobs as a photographer is to keep competing photographic factors, like shutter and aperture, in balance. You know that low ISO settings give you the least digital noise. But you can't shoot at ISO 100 all the time--if you could, that would be the only setting on your camera.

Instead, shoot with the lowest ISO you can get away with for the current photographic conditions. Bump up your ISO when you're shooting indoors without a flash, for instance, but don't crank it all the way to ISO 1600 when ISO 800 might do. Just increase the ISO until the shutter speed is fast enough to take a sharp photo, which is usually something like the inverse of the focal length. Here's an example: If the lens is set to 100mm, you can probably get a fairly steady shot with a shutter speed of 1/100 second.

And when you're done shooting in low light, remember to reset the ISO to the camera's lowest setting. Don't leave it on Auto, where your camera can change the ISO willy-nilly.

Likewise, longer exposures can lead to extra noise, but you can fight back by turning on your camera's built-in noise reduction. Many cameras have an automatic noise reduction feature that kicks in when the shutter speed exceeds 1 second. Check your camera's user guide for instructions on how to turn on that handy feature.

Finally, it's useful to remember that underexposure leads to noisier photos than overexposure. Overexposure has its own problems, of course. An overexposed shot can have "blown out" highlights of pure white, and no amount of tweaking in a photo editor will fix it. If your camera has an exposure bracketing feature, you might want to take a series of photos of important shots so you can keep the best one.

Try Some Noise Reduction

If you just can't avoid a little noise, you can smooth out your photos with software. Many photo editing programs come with some sort of noise reduction filter. In Adobe Photoshop Elements 6, for example, you can find it by choosing Filter, Noise, Reduce Noise. Here, in the same way you have to contend with trade-offs between ISO and noise, you have to weigh the trade-off between reducing noise and erasing useful details in the photo. You can see the effect of both extremes in Photoshop Elements.

With the Strength set low and Preserve Detail set high, the image is crisp and sharp, but also unattractively grainy.

With the Strength set high and Preserve Detail low, the image loses sharp detail and takers on a "soft focus" sort of glow.

You can also try a stand-alone noise reduction program. I discussed two good choices--Noiseware and Noise Ninja--in "Eliminate Noise From Your Photos," mentioned above.

Hot Pic of the Week

Get published, get famous! Each week, we select our favorite reader-submitted photo based on creativity, originality, and technique.

Here's how to enter: Send us your photograph in JPEG format, at a resolution no higher than 640 by 480 pixels. Entries at higher resolutions will be immediately disqualified. If necessary, use an image editing program to reduce the file size of your image before e-mailing it to us. Include the title of your photo along with a short description and how you photographed it. Don't forget to send your name, e-mail address, and postal address. Before entering, please read the full description of the contest rules and regulations.

This Week's Hot Pic: "Ballerina in Waiting" by Samantha Denys, Detroit

Samantha writes: "I was backstage at a Christmas performance with my Canon Digital Rebel XSi. I saw some of the dancers waiting to go on stage and snapped this shot of the girl's pointe shoes. I edited the picture in Photoshop to give it some more character."

This Week's Runner-Up: "Cat in Window" by Marcia Bickel, Harper, Kansas

Marcia writes: "I shot this with a Canon A540. I thought the sunlight around the cat made it look like he was glowing."

See all the Hot Pic of the Week photos online.

Have a digital photo question? Send me your comments, questions, and suggestions about the newsletter itself. And be sure to sign up to have the Digital Focus Newsletter e-mailed to you each week.

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