You might think your images are quiet, hanging out as visual entities. But if there are random, extraneous pixels that aren't part of the image detail, they actual contain noise.
Where does noise come from? You can end up with noise in scanned images resulting from a scanning sensor or from a grain pattern in the scanned film. In digital images, noise can occur when you use a high ISO setting on a digital camera, or if the image is underexposed, or if you shoot a picture in darkness with a long shutter speed. You can even get noise if you oversharpen an image.
However it gets there, if it distracts from the story you're trying to tell with your image, you probably want to get rid of it. The good news is that Photoshop includes noise reduction tools. The bad news is that removing noise is tricky and may not always be completely possible.
There are two kinds of noise:
- Luminance noise is grayscale data that can make an image look grainy.
- Color noise shows up as colored artifacts in your image. Color noise is typically easier to remove than luminance noise.
You can use the noise reduction filter in Photoshop, but the newer filters in Camera Raw usually do a better job. Keep in mind that noise reduction is usually achieved by blurring the image a bit so that the noise blends in with the rest of the image. So, you'll want to restore some detail after you reduce noise. As with many aspects of image editing, the goal is to strike a balance.
To remove noise in Photoshop:
- Choose Filter > Noise > Reduce Noise.
- Click the plus button below the preview window to zoom into an area that contains noise, so you can clearly see how it changes as you adjust the settings. You can drag the preview to focus on different areas of the image.
- Keep an eye on the preview window as you adjust the Strength, Preserve Details, Reduce Color Noise, and Sharpen Details sliders. Strength reduces luminance noise; Reduce Color Noise removes chromatic noise.
- If you're comfortable working with channels, you can select Advanced, and then click the Per Channel tab to specify luminance noise removal in each channel.
- Click OK to apply your changes.
Figure 4.23 The Reduce Noise filter is pretty good at removing color noise, but not quite as accurate when it comes to luminance noise.
To remove noise in Camera Raw:
- Open your image in Camera Raw. Remember that Camera Raw can open only TIFF, JPEG, DNG, and raw image formats.
- In Camera Raw, click the Detail tab.
- Zoom in to at least 100 percent to preview the changes you're making.
- Move the Luminance slider to remove luminance noise, and then adjust the Luminance Detail and Luminance Contrast sliders to restore some detail and contrast to the image.
- Move the Color slider to remove color noise, and then adjust the Color Detail slider as well.
Figure 4.24 If noise is a serious problem in your image, take advantage of the Detail pane in Camera Raw to remove it.