Tuesday, December 16, 2008
Sharp Is King
Strategies for waging the war between higher ISOs, sharpness and noise
The Downside Of Higher ISO
Here’s where the compromise comes in. While the newest D-SLRs offer greatly improved results at remarkably high ISOs, we’re still sacrificing some image quality every time we click that dial upward. Today, maximum image quality is achieved at ISO 100-200 on a camera with a full-frame sensor and the latest in-camera processor. The result is a sharp, finely detailed image. As you increase the ISO setting, the sensor becomes more sensitive, not only amplifying the light from your subject, but also random signals from other sources. The effect has been likened to increasing the volume of a radio with poor reception—both the program and the static get louder. The smaller and more tightly packed the megapixels, the more the sensor itself generates noise. The in-camera processor’s job is to filter out background noise while accurately rendering the image information to the recording media. The less efficiently the noise is filtered, the more it remains in, and degrades, the image.
There are two kinds of noise found in a digital image. One is luminance, colorless, granular variations in lightness that give an effect like film grain. Luminance is the most predominant type of noise in a digital image and the source of some textural detail. The second, more damaging kind of noise is chrominance, an array of green, magenta and blue specks. Chrominance is most evident in un-detailed expanses of a single tone, such as the sky. There’s nothing good to say about chrominance noise in an image. Excessive noise masks detail and sharpness in an image and causes color aberrations.
It’s best to control noise before it becomes a nuisance. Resist the temptation to use ISO settings beyond the threshold of your camera’s abilities. Point-and-shoots with pixel-packed small sensors are pretty much limited to the lower ISOs, while recent full-frame D-SLRs have much greater capabilities in higher ISO ranges. Captures at up to ISO 800 have produced relatively noise-free images in our tests with a prototype of the new Canon EOS 5D Mark II.
Noise is most prominent in underexposed, dark areas of an image. Using multiple-capture HDR (High Dynamic Range) techniques can minimize, or even eliminate, noise in dark areas. Whenever insufficient light is an issue, use a tripod and carefully balance your ISO, shutter speed and aperture to achieve the highest-quality image possible.
When conditions demand the higher ISOs that undoubtedly will produce noise, postcapture software programs can save the day. These programs do more than simply smooth the mosaic of your noisy image; they allow you to choose the level of detail you want to retain (the textural grain) while restoring sharpness and resolving color anomalies to your preferences. Four of the best-known are Dfine 2 (www.niksoftware.com), Noiseware (www.imagenomic.com), Neat Image (www.neatimage.com) and Noise Ninja (www.picturecode.com), but there are many others.
Page 2 of 3
Get 11 Issues of Outdoor Photographer for only $14.97!
That's 77% off the cover price!