Noise can ruin an otherwise perfect picture. Photoshop and other tools can help you reduce image noise and rescue your photographs. Digit shows you how.

Using your camera’s menus to increase the ISO setting helps you capture tricky shots and expand your picture-taking options – but at a cost.

Raising the ISO will also increase the amount of image noise – unsightly flecks that can make it look as if you took your picture during a digital snowstorm. Because image editors have trouble distinguishing these errant particles from legitimate image details, removing noise can be a challenge. Both Adobe Photoshop Elements 3 and Photoshop CS 2 provide a Reduce Noise filter that can minimize image noise. But getting the best results requires a deft touch.

What causes noise

When you raise your camera’s ISO setting, you essentially make it more sensitive to light. This makes low-light photos easier to shoot because exposure times are shorter, decreasing the chance of blurring. By day, the faster shutter speeds help freeze action. To get these results, a digital camera amplifies the data that hits its sensor. But it’s like a radio – when you turn up the volume on a weak signal, the static gets louder, too. At moderate ISO settings, such as 200, noise tends to be subtle. But at high ISO speeds – 400 or higher – the noise can be overwhelming. It’s especially noticeable in areas containing minimal detail, such as a blue sky, a smooth-cheeked model, or blurred backgrounds.

Basic noise reduction

Although the noise in every image is different, the steps for solving the problem are similar in Photoshop CS 2 and Photoshop Elements.

First, you need to open the noisy photo and make a copy of its background layer by pressing Command-J. Then, select the duplicate layer in the Layers palette and choose Filter: Noise: Reduce Noise.

In the Reduce Noise dialog box, drag the Strength slider to the right to increase the amount of noise reduction. As you do this, areas containing fine detail will begin to blur. To minimize the blurring, drag the Preserve Details slider to the right. Alternate between the two sliders until you’ve found a happy medium. Your goal is to reduce the noise where it’s most apparent without introducing obvious blurring in areas containing fine details.

Inexpensive digital cameras tend to produce chrominance noise, which can look like splotchy green or pink stains. If your photo also suffers from this type of noise, drag the Reduce Color Noise slider to the right until the colour becomes less noticeable.

If you’re using Photoshop CS 2, you’ll see a couple of additional options in the Reduce Noise dialog box. For example, you can use the Sharpen Details slider to restore some crispness to a photo. Click on the Advanced radio button, and you can isolate individual colour channels (red, green, and blue) and apply different noise-reduction settings to each. Depending on your camera and the subject of your photo, you may find that most of the noise is in just one colour channel. Finally, click on OK when you’re satisfied.

Taking it further

If you’re happy with the photo, you can stop here. In many cases, however, the Reduce Noise filter blurs areas containing fine details.

With a little extra work, you can get the best of both worlds – sharp details and less noise. The trick is to selectively blend the filtered layer with the original layer beneath it. This technique lets you apply noise reduction only to an image’s most apparent noise. It also lets you be more aggressive when removing noise in the first place, since you’ll be able to restore detail lost in the process.

For maximum control when blending layers, do what the professionals do – use a layer mask on the filtered layer. Layer masks let you selectively hide a layer’s pixels (thus revealing the underlying layers) without actually erasing any data, so you can easily restore the pixels later. This approach lets you experiment without worrying about permanently altering your image.

To create a layer mask in Photoshop CS 2, select the duplicate layer in the Layers palette and click on the Add Layer Mask button at the bottom of the Layers palette. Click on the new layer mask to select it.

Clicking on the Add Layer Mask button attaches a layer mask to your filtered layer. Painting on this layer with black reveals the underlying image.

Select the Brush tool from the Tools palette and choose an appropriate brush size from the Tool Options bar. Set the brush colour to black, and paint over the areas where important detail was lost. As you paint, you’ll reveal the details in the underlying layer.

If you go too far and uncover some of the original noise, switch the brush colour to white (press the X key to do this quickly) and paint back over the area. This will return the pixels in the filtered layer to full opacity. Alternate between painting with black and white until you find the best blend of the two layers.

Elements’ secret layer mask

Photoshop Elements doesn’t have a layer-mask feature, but you can simulate one by using a fill layer. Go to Layer: New Fill Layer: Solid Color. Choose any colour in the dialog box that appears. Then click on OK.

In the Layers palette, drag the new fill layer below the layer you want to mask – in this case, the duplicate layer with the Reduce Noise filter applied.

Select that duplicate layer and press Command-G. This groups it with the fill layer. At this point, the fill layer will act as a layer mask. As with layer masks in Photoshop CS 2, you paint on it with black to reveal the underlying layer, or paint with white to hide it.

When eliminating noise, remember that you’ll get more realistic-looking results if you apply noise reduction judiciously. Go overboard, and you’ll end up with artificial-looking images.

Plug-in to noise reduction

If Adobe’s Reduce Noise filter doesn’t quiet photos to your satisfaction, you may want to shop for a noise-reduction plug-in. Numerous products are available for Photoshop CS 2 and Elements alike, and some are also available as stand-alone programs. All of them provide more-aggressive noise reduction than Photoshop’s Reduce Noise filter. They also make it easier to create an artificial-looking image, though, so use them carefully.

Kodak’s Digital Gem is an inexpensive option ($49, around £27). It’s easy to use (something that can’t be said of most other noise-reduction plug-ins), and its built-in sharpening feature lets you restore some of the detail that the noise-reduction process removes.

Kodak also offers Digital Gem Professional ($99, around £55), which boasts more control without too much more complexity. It lets you blend the filtered and unfiltered versions of your image to restore detail and avoid artificial-looking results. And unlike Digital Gem, it works on 16-bit images – important if you’re an advanced photographer working with RAW-format photos.

For an obsessive level of control over noise reduction, check out PictureCode’s Noise Ninja. The 8-bit version costs $45 (around £25), and a 16-bit version costs $80 (around £45). Noise Ninja relies on profiles that describe a particular camera’s noise characteristics, so you can have Noise Ninja build a profile specific to the image you’ve opened. Noise Ninja also provides a unique “noise brush” that lets you selectively restore details in a way that’s similar to using a layer mask.

Noise Ninja is also available as a standalone program. Another option is to run Photoshop plug-ins using Lemke Software’s GraphicConverter X ($35, around £20), but if you’re serious enough about your photography to be considering third-party noise-reduction software, you’d be better off splashing out on a copy of Photoshop.