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Note:
Photoshop tools and menus are used here as examples which may be
different from other image editing programs.
Reducing Noise
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Image noise appears as random extraneous pixels
that aren’t part of the image detail. Noise can be caused by photographing with
a high ISO setting on a digital camera, underexposure, or shooting in a dark
area with a long shutter speed. Scanned images may have image noise caused by
the scanning sensor. Often, the film’s grain pattern appears in the scanned
image. Image noise can appear in two forms: luminance (grayscale) noise, which
makes an image look grainy or patchy, and color noise, which is usually visible
as colored artifacts in the image. These small detail errors appear as part of
the photographic detail of the digital image and become visible as bright,
colored, or dark specks. When visible, noise can distract the viewer and create
an unnatural appearance in a digital image.
Digital camera noise can be categorized into two main types:
1. Luminance Noise is noise that appears as small, dark spots that often look
like film grain.
2. Chrominance Noise is noise that appears as small off-colored spots or specks
in the
image.
To reduce image noise and JPEG artifacts:
1 Choose Filter > Noise > Reduce Noise.
2 Zoom in on the preview image to get a better view of image noise.
3 Set options:
Strength 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 controls to fine-tune
noise reduction.
Reduce Color Noise Removes random color pixels. A higher value reduces more
color 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.
Remove JPEG Artifacts Removes blocky image artifacts and halos caused by saving
a image using a low JPEG quality setting.
If luminance noise is more prevalent in one or two color channels, click the
Advanced button and then choose the color channel from the Channel menu. Use the
Strength and Preserve Details controls to reduce noise in that channel.
Plug-in Filters
Dfine|
Dfine™ provides a wide range of options for reducing noise and optimizing detail
in digital images. Using an easy-to-use four-step process, you can choose to
reduce varying types of noise and artifacts including luminance noise,
chrominance noise, and JPG artifacts. You can also use a variety of features in
Dfine™ to
enhance color and contrast in an image while considering the effects of the
noise reduction process. Dfine™ uses a unique and powerful system that enables
you to reduce noise generated in the camera through its camera profiling system.
Each camera profile combines a powerful noise controlling function that works in
conjunction with the camera’s characteristics by drawing a detail-to color
correlation in the image. The camera profile controller enables noise reduction
to be applied across the image in a natural and flexible manner. The user first
identifies different color ranges that require specific levels of noise
reduction, and then adjusts the amount of noise reduction against the indicated
color accordingly. Camera profiles have been developed for most current digital
camera models from major manufacturers and will continually be updated for
future camera models.
Noise Reduction
The Image Factory Noise Reduction is another powerful plug-in for Photoshop to reduce several types of digital image noise.
This plug-in shows the results of its calculations in a preview pane. To better judge the effect of your settings the preview can be zoomed by the zoom-buttons below the preview pane indicated with a "+" (plus) and "-" (minus) symbol.
Noise in digital images can appear as noise in luminosity, and noise in color. The former usually consists of small random darkness dots, the latter as cloudy, fluid color differences. The size parameter designates the size of the luminosity noise, and should be set to a value that is just
one or two pixels larger than the size of the noise.
If you set the Reduction slider to 100%, then the size slider can easily be set to a value where the noise seems to disappear
The reduction of noise can be set using the reduction slider. It should be set at the point where the noise disappears, but the image seems to retain its sharpness. First set this slider to 100%, then adjust the "size" parameter to the level desired, then move this slider all the way to the left. You should now see the original noise. Now slowly move this slider to the right until you reach the desired result.
Digital images usually suffer the most noise in the dark tones. Hence, the noise reduction
plug-in primarily corrects the darker tones of the image. If the noise is quite severe, it may also affect the mid-tones. These can be set separately using this slider.
Because color noise is usually very different from noise in luminosity, a separate slider is available that controls color noise independently from all other parameters. Use this slider for any color noise
artifacts, including mild color fringing problems.
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