Monday, November 12, 2007
Trick Shots: Low Light
Discover how high ISOs can improve the quality of your photographs
The Importance Of Exposure
Exposure is always important when photographing, but it's especially essential when shooting under low-light conditions and high-ISO settings. Underexposed images increase the presence of noise, especially when you attempt to correct for it in Photoshop. Pulling out shadow detail from an underexposed shot often only succeeds in making the presence of noise more obvious.
So, it's important to obtain as accurate an exposure as possible, and few things are better for achieving this than the camera's histogram. This graphic representation of image tonal data, from the brightest white to the darkest black, is a great reference for knowing whether you're risking increased noise because of severely underexposing your images.
To avoid blowing out the highlights, some photographers will lock in a -1⁄3 or -1⁄2 exposure compensation on their camera. This can be a real drawback when shooting under low light at high ISOs, however, resulting in images more underexposed than necessary. By referring to the histogram, you can make a more concise assessment of lighting and exposure, ensuring that you maintain maximum highlight and shadow detail.
For photographing performances, I'll shoot in manual mode. Automatic exposure modes, such as aperture priority and shutter priority, can be unduly influenced by dark and light elements in the frame. This results in shifts of exposure that can diminish image quality. As I'm often photographing scenes in which the background falls into deep black because of light falloff from the stage lights, the camera can be easily fooled into using a longer exposure than is necessary, risking overexposed images. By sticking to manual, I avoid such problems and ensure consistently exposed photographs. If the lighting changes, it's a quick thing to take a test shot, evaluate my histogram and make any necessary adjustments.
Exposure is also important if you're shooting time exposures, though you also have the benefit of in-camera noise reduction, which reduces the presence of noise while the sensor remains charged for lengthy periods of time. The drawback is that this requires longer processing times, an issue that's often unacceptable when shooting performances. For nightscapes, however, engaging the camera's noise-reduction feature is a good choice.
Reducing the presence of noise in digital files after the fact has been made easy by a host of applications, which attempt to strip the noise from the image while maintaining image quality. While Adobe Photoshop and other image editors include some level of noise reduction, there are many third-party plug-ins that offer a myriad of ways of eliminating noise. Alien Skin Image Doctor, Auto FX AutoEye 2.0, Imagenomic Noiseware, Nik Software Dfine and PictureCode Noise Ninja, are just a few of the applications that can evaluate a file and separate noise from the actual image data.
These applications often do a remarkable job at reducing noise, but there's often a slight loss in overall sharpness that results. However, all these applications provide fine-tuning features that allow you as the photographer to have complete control over how subtle or aggressive the noise reduction will be.
Though noise is certainly something to be aware of, the benefits of high ISOs can prove worthwhile, especially when it comes down to getting the shot or not.
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