Eliminate Noise From Your Photos
- — 07 February, 2006 15:57
The ability to change your digital camera's ISO level is a mixed blessing. Increasing the ISO allows you to capture sharp pictures in low light by increasing the camera's sensitivity, but it also adds unwanted digital noise to your picture--which looks like the grain you'd see in a print made from very fast 35mm film.
Previously we talked about how you can use ISO to your advantage; in this Here's How, let's see how to minimize the noise that accompanies higher ISO levels.
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. In my example, you might not notice the noise at first. But check out a small detail of the original image and you'll see a lot of noise, both in the background and in the girl's face.
Minimizing 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, then reduce it even further on the PC.
Use higher ISO values only when you need to; the lower your ISO, the less noise you'll get in your photos. Also, check your camera's settings for a noise-reduction mode. Many digital cameras--especially models that support very high ISO levels--have a menu setting that reduces noise when the ISO is set at 800 or higher. It's a good idea to turn this on.
Reducing Noise on the PC
After you take your photos and transfer them to your computer, you can work some digital magic. Many image editors, including Corel's Paint Shop Pro and Adobe's Photoshop Elements, have a noise-reduction filter. In Paint Shop Pro, for instance, you can choose Adjust, Photo Fix, Digital Camera Noise Removal and use the default settings. In Photoshop Elements, you can find a similar feature by selecting Filter, Noise, Reduce Noise.
Try a Noise-Reduction Program
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. For better results, check out the commercial version of Noiseware.
Truth be told, I like Noise Ninja even better. 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 Autofill. Then save the profiles. (Don't worry about memorizing all this; Noise Ninja comes with complete instructions on setting up your profiles.) Once that's done, the program automatically loads the right profile whenever you open a digital image file.
Want to see the kind of results you can get? Take a look at my sample picture again, after I ran it through Noise Ninja.