If you’ve used a compact digicam to take digital photos in dim lighting with high ISO settings, your shots will probably be noise-affected. And, even if you’ve used a digital SLR camera, you may find it’s almost as noise prone with long exposures, regardless of the sensitivity setting. To complicate matters, JPEG compression-related artefacts can cause image noise to be more visible, making otherwise great shots unprintable.

 

If you’ve used a compact digicam to take digital photos in dim lighting with high ISO settings, your shots will probably be noise-affected. And, even if you’ve used a digital SLR camera, you may find it’s almost as noise prone with long exposures, regardless of the sensitivity setting. To complicate matters, JPEG compression-related artefacts can cause image noise to be more visible, making otherwise great shots unprintable.

The latest version of Photoshop has a handy tool that can suppress most image noise without compromising picture quality. But before using it, there are a few caveats to take into account.

All noise-reduction systems work best on images that have not been sharpened – either in the camera or in editing software. Sharpening makes the unwanted artefacts more visible so you should avoid in-camera sharpening (or set the sharpening control to low) when you take the shot and reserve any post-capture sharpening until after noise removal processing.

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sampleimage-475

This sample image from a compact, 5-megapixel digicam is visibly noise affected due to shooting at ISO 400.

Step 1: Start by opening the image file in Photoshop CS2. Click on the Magnifying Glass in the toolbar and zoom in to 200% so you can view the image noise. Activate the Channels palette and click on the RGB composite channel.

Step 2: View each colour channel separately by clicking on the ‘Eye’ icon beside each channel (this turns the channels on and off). It is not uncommon to find one channel (often Blue) has more random noise than the others, although, with this image, all three channels are almost equally affected.

Step 3: Select Filter>Noise>Reduce Noise to open the adjustment dialog box. The default setting is Basic. Set all the fields to zero as a baseline. Clicking on the Remove JPEG Artifact box allows you to see the extent to which the image is affected by JPEG compression.

Step 4: Drag the Strength slider to the right and watch how the image softens as the random-coloured pixels disappear. If most of the noise is colour noise, setting this slider to full strength will be overkill so knock it back to 7 or 8. Adjust the Preserve Details slider to restore the detail lost with the Strength adjustment. Then experiment with the Reduce Colour Noise and Sharpen Details sliders to gain the best balance between noise suppression and detail retention.
Step 5: Clicking on the Advanced button just below the Preview check box allows you to view the individual channels in the image and adjust them selectively. Buttons below the preview image allow you to enlarge the preview so you can clearly see the channels at pixel level. Adjust any channel that still has some residual noise by using the slider below the channel preview. (The Blue channel is often the most noise-prone so it’s a good starting point for individual channel adjustments.)

Step 6: Click OK to apply the noise reduction settings.