Pumping Up and Down the Noise in Photoshop

Pumping Up the Noise
Noise in images consists of any graininess or texture that occurs, either because of the inherent quality of the image or through the editing process. Noise filters, like the Photoshop Add Noise plug-in, produce random texture and grain in an image. If you’re new to image editing, you might wonder why you’d want to add noise to an image in the first place. Wouldn’t it be smarter to remove it? In practice, though, you’ll find lots of applications that call for a little noise here and there:
- To add texture: Objects that become too smooth, either because of blurring or other image editing you may have done, often look better when you add some noise to give them a texture. This technique is particularly useful if one object in an image has been edited, smoothed, or blurred more than the other objects in the image.
- To blend foreign objects into a scene: When you drop a new object into the middle of an existing scene, you’ll often find that the amount of grain or noise in the new object is quite different from the objects it’s joining.
For example, say you’ve decided to take a photo of your house and want to insert a certain luxury car in your driveway. Unfortunately, your digital photo of your brother-in-law’s luxo-mobile is a lot sharper than the picture of your house. Adding a little noise can help the two objects blend more realistically. You may even forget that the car isn’t yours.
- To improve image quality: Images that contain smooth gradients often don’t print well because many printers (especially older ones) are unable to reproduce the subtle blend of colors from one hue to another. The result is objectionable banding in your printed image: You can see distinct stripes as the colors progress from one to another in the top image. Adding a little noise can break up the gradient enough that your printer can reproduce the blend of colors, and the noise/grain itself is virtually invisible on the printed sheet.

Pumping Down the Noise
Although many Noise filters add grain, other filters in the Noise submenu don’t add noise at all; instead, they make noise and artifacts like dust and scratches less noticeable. Choose Filter-->Noise to find your tools, which include
- Despeckle: This filter makes dust spots in your image less noticeable by decreasing the contrast of your entire image — except at the edges. That translates into a slightly blurry image (which masks the spots) that still retains sharpness in the edges of image components. You end up with a little blur to soften the image, but enough detail in the edges that the picture still looks good.
- Dust & Scratches: This filter concentrates its blurring effect only on those areas of your image that contain scratches and other artifacts. Photoshop performs this magic by looking at each pixel in an image, moving out in a radial direction until it encounters an abrupt transition in tone. (That’s a signal that a spot or scratch has been found.) You can specify the radius Photoshop searches for the little culprits, from 1 to 16 pixels. Be careful not to overdo it. Too much of this filter can obliterate the detail in the image. While working with any of the Noise filters, it’s best to be very conservative at first. All the Noise filters involve destruction of image data. A little bit can help and be just the effect you’re looking for. Just a little bit more, however, may completely wreck things.
- Median: This filter reduces contrast around dust motes, thus hiding them, in a slightly different way. This filter looks at the pixels surrounding each pixel in the image and replaces the center one with a new pixel that has the median brightness level of that group. The process is a little hard to describe succinctly, but basically, the bright spots darken while the rest of the image isn’t affected.