100 in 100: Reduce noise with LAB

100 photography tips in 100 days: Day 94

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Have you ever looked at your camera's LCD screen and been completely happy with the overall look of your images--only to later realize that they are full of "noise"?

Digital camera noise can take on a number of looks. It can look of big grains of sand across the whole image, or a lack of detail in dark areas, or colorful "specs" in the light or dark areas of your image.

Noise is usually the result of underexposure or by setting your camera's ISO at a high level (each camera behaves differently). Long exposures or a very warm environment can also contribute to high noise levels. Very small imaging sensors, like those found in most cell phones, often produce images with significant noise (especially color noise). Using cameras with sensors that have larger photo sites (like many DSLRs) and shooting in RAW (when possible) can help to reduce noise because of the added control you have after the shot.

What can you do to reduce noise? One approach is to convert to LAB space in Adobe Photoshop, and blur the A and B channels using Gaussian blur or the Dust and Scratches filter. The A and B channels represent the color information in a file, so by targeting the color detail, you can reduce the color noise.

LAB Work

Below is a quick tutorial for reducing color noise in Adobe Photoshop CS/CS2/CS3. (Note: I like to credit the "author" of the tip if it is not my own. This tip has been passed around the imaging community for so many years, I'm sorry to say I don't know who deserves credit for it. Also, there are a number of variations of this tip so I recommend searching for others and experimenting for yourself.)

Before running the color noise reduction procedure.

Closeup view before running the color noise reduction procedure.

Step 1: Convert your flattened RGB file to Lab Color Mode (Image>Mode>Lab Color). Files can be in 8-bit or 16-bit color. (16-bit is recommended to use if you shoot in RAW.)

Converting from RGB to Lab Color Mode.

Step 2: In your Channels Palette, choose the "a" Channel, or press Cmd+2 (Mac) or Ctrl+2 (Windows). Then choose Filter>Blur>Gaussian Blur until you see the detail become blurred (this is subjective of course; don’t overdo it). For a 6 to 10 megapixel camera file, about 2-5 pixels is recommended. (As mentioned earlier, you can also choose Filter>Noise Dust and Scratches, which allows more overall control. Test to see which works best for you.)

The a channel shown before blurring.

Step 3: In your Channels Palette, choose the "b" Channel, or press Cmd+3 (Mac) or Ctrl+3 (Windows). Then choose Filter>Blur>Gaussian Blur until you see the detail become blurred as described in Step 2.

Choosing Gaussian Blur from the Photoshop menu.

The a channel shown after blurring with an amount of 3.4 pixels.

Step 4: Convert your file to RGB or CMYK, depending upon how the images are going to be used.

Closeup view after running the color noise reduction procedure.

After running the color noise reduction procedure.

Noise (or grain) in photos is not all bad. I will often add noise to images to make them look more more "natural." Noise often gives images a sense of added sharpness. A lot depends on your output device and media. Some monitors, projectors and printers will show the grain more, and some will show it less, and every paper will also render images differently.

See this previous "100 in 100" tip for more information about reducing grain.

Andrew Darlow is a photographer, author and digital imaging consultant based in the New York City area. He is editor of The Imaging Buffet, an online resource with news, reviews, and interviews covering the subjects of digital photography, printing, and new media. Portions of this article are excerpted from Darlow's new book, 301 Inkjet Tips and Techniques: An Essential Printing Resource for Photographers.

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