Digital noise correction
By Eugene Struthers
In this months editorial - tutorial. I will be demonstrating how to reduce, correct or eliminate "Digital noise" from your images. To fully appreciate the dynamics of this article. You would have needed to have read last months editorial How to correct the Colour balance in an image (Part II).
What is Image noise?
Image noise can appear as random extraneous pixels that aren’t part of the image detail. Noise can be created when a photographer uses a higher ISO number setting on their digital camera. It can also be created if they shoot at night or in dark area's with a long shutter speed, or they deliberately want an image to come out underexposed.
Lower end Compact consumer cameras usually exhibit more image noise than high-end digital SLR cameras. Scanned images may have image noise caused by the scanning sensor. This can often cause the film’s grain pattern to appear in the scanned image.
Image noise can appear in two forms: luminance (grayscale) noise, which makes an image look grainy or patchy, and colour noise, which is usually visible as coloured artifacts in the image.
We first need to open an image in Photoshop. The image above was opened using Photoshop CS5.
Choose Filter and scroll down to Noise and across and down to Reduce Noise.
I've Zoomed in to the image approximately 200% to get a better view of the digital image noise.
As you can see from the image above. This image has a lot of Digital Noise. Especially around the models face, her hair, the gold necklace and the whites of the sky. These are indicated by the red arrows above.
The Reduce Noise dialog box that appears, will be default to its own Photoshop CS5 settings. So before continuing, untick the Remove JPEG Artifact box. And add a tick into the Preview box.
The Strength slider bar controls the amount of luminance noise reduction applied to all image channels.
Preserve Details: Preserves edges and image details such as hair or texture objects. A value of 100 preserves the most image detail, but reduces luminance noise the least. Balance the Strength and preserve details control to fine-tune noise reduction.
Reduce Colour Noise: Removes random colour pixels. A higher value reduces more colour noise.
Sharpen Details: Sharpens the image. Removing noise reduces image sharpness. Use the sharpening control in the dialog box or use one of the other Photoshop sharpening filters later to restore sharpness.
Strength:- 10
Remove JPEG Artifacts removes blocky image artifacts and halos caused by saving a image using a low JPEG image quality setting.
If luminance noise is more prevalent in one or two colour channels, click the Advanced button and then choose the colour channel from the Channel menu. Use the Strength and Preserve Details controls to reduce noise in that channel.
Luminance noise: may be more pronounced in one channel of the image, usually the blue channel. You can adjust the noise for each channel separately in the Advanced mode. Before opening the filter, examine each channel in your image separately to see if noise is prevalent in one channel. You preserve more image detail by correcting one channel rather than making an overall correction to all channels.
Final result
