Thread: Reduce and eliminate 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. Let's explore what noise is all about and how to minimize it in your photos.

Identifying Noise
What does digital noise look like? Dots, speckles, and smudges of random color. Noise is easiest to see in regions of regular color. You can see it in skin tones or on a wall in the background, for instance. 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.

What Causes Noise People often compare digital noise to old-fashioned film grain, and for good reason. Not only do they look some what 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 exposure right when you take the picture.

Minimising Noise in the Camera
Your battle against noise can be a two-pronged attack. You can help minimize it in your digital camera before you take the photo, and then reduce it even further on the Pc. 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 cati't shoot at ISO 100all 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 nois'e 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 underexpo sure 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.

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.

Imagenomic offers a free version called Noiseware Community Edition, which is handy for getting your feet wet. I don't recommend it as your main weapon against digital noise, though, because the program limits you to saving your finished pictures at a JPEG quality level of 90 percent. I think that defeats the whole purpose of using the program to begin with, since you can't resave the image at the highest quality. Instead, I recommend that you purchase the commercial version of Noiseware.

Truth be told, I like Noise Ninja even better. You can get the "home license" for $35 or the pro version for. What's great about Noise Ninja is that it lets you create a custom noise profile for your particular digital camera and use it to accurately remove unwanted noise while doing the least damage to your photos.

That might sound intimidating, but it's really pretty simple. What you need to do is display Noise Ninja's Profile Chart; it's a colored grid available in the program's File menu. Then take a series of pictures of the chart while it's displayed on your computer screen. Take a photo at each of your camera's various ISO settings, leaving the picture slightly out of focus as you do so; it will help to switch your camera to manual focus mode for this. If you've got a CRT monitor, you'll want to use a slow shutter speed so you don't accidentally capture any dark bands on the computer's screen.

Next, load the photos into Noise Ninja and click the Profile Chart button. Click the Edit Profile Annotations button and click Auto fill. Then save the profiles. Once that's done, the program automatically loads the right profile whenever you open a digital image file. The next time you open up an image file in Noise Ninja, you can utilize the profile you have saved.

Try a Noise-Reduction Program You'll get better results, though, with a program custom-made to eliminate digital noise. Imagenomic's Noiseware Reducing Noise on Your PC.