Quieting Noise; Digital Noise Is Easily Controlled With These Plug-In Filters Page 3

When all was said and done, I came away with one favorite: Noise Ninja, though it did not deliver a decisive blow to the competition. Sometimes I had to go into Photoshop to further tweak the image with the Median noise filter, then sharpen. But I liked the way it transformed luminosity noise into more uniformly distributed grain patterns and smoother textures (in contrast to the uneven performance of the other plug-ins), doing so more consistently. And Noise Ninja handily dealt with color noise, especially the more tenacious high-frequency variety. And all this without much effort from me.

(Top): NR plug-ins are not designed to deal with long-exposure noise ("hot pixels" that are "burned" into the image, hence more resistant to conventional NR). Long Exposure NR is a special camera function designed to deal with this problem. However, the hot pixels which appear as bright spots or streaks (circled) in this 3-minute exposure were sporadic enough to correct in post. (Image magnified to 300 percent.) (Above): Take noise reduction too far and the image looks plastic, losing considerable detail. I may have rid the picture of luminosity and color noise, but now this set looks more fake than ever.

When using presets, Noiseware often produced images that were too plastic or that needed some touching up afterward. However, the plastic factor could be dealt with easily enough by modifying the helpful presets--the Landscape preset proved especially handy. Still, all those sliders? I recommend that you don't click those tabs unless you really, really have to. Having said that, Noiseware was my first NR plug-in and remains a sentimental favorite.

Dfine did a competent job when set to Automatic mode, but I found that dealing with control points could be hit or miss--you really have to target every conceivable area to do a good job, and even then it did poorly with heavy color noise. And it was slow, compared to the other plug-ins. Neat Image produced the poorest results, with images that were either too plastic or simply not corrected to my satisfaction. The small window was also a hindrance. But, at the end of the day, I'd be very happy working with any of these plug-ins. In saving time and effort, each is a marked improvement over what an image editor can do alone.

In Camera Noise Reduction (NR)
Good news. The camera may provide an effective means of dealing with long exposure (fixed-pattern) noise. Long exposure NR is a camera function that utilizes the principle of "dark frame subtraction." Essentially, the camera makes two exposures at the same shutter speed and f/stop, except that the second exposure is a dark frame with no image--except for hot pixels. These hot pixels tend to burn through the image, similar, in a sense, to the spots you see after glimpsing a bright light source, except that they don't simply fade away over time. Specially formulated algorithms are brought to bear in precisely layering and blending the two images so as to subtract the noise, which is the one common element shared by the two exposures. (For those of you with cameras that don't offer this feature, dark frame subtraction can also be performed manually in post--but as a somewhat laborious procedure. Details can be found in the online references listed later).

While this 35mm slide scan didn't appear that noisy at first, close inspection revealed both luminosity and color noise (which was the more disturbing of the two) (Top). Of the four noise filters tested, Noise Ninja did the best job, giving me a more uniformly distributed grain pattern, while getting rid of the color sprinkles (Above). Dfine and Noiseware were in a virtual dead heat for second place. Neat Image left the most color noise, though this was still an improvement over the original.

Good and bad. High ISO NR is another digital camera function accessed through the menu, but this one is designed to deal with noise associated with high ISO values. But I found its effect to be negligible (at least when tested on the Nikon D300 at the maximum NR setting).

Additional Resources Online
Do an online search for "digital noise" and, if your camera doesn't offer long exposure NR, also search "dark frame subtraction." Many of the site names were too complex to list, but here are two for starters: www.cambridgeincolour.com/tutorials/noise.htm and www.photo.net/learn/dark_noise.

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