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                    Reduce image noise and JPEG artifacts
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                <div><div class="section"><p>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. Low‑end consumer cameras usually
exhibit more image noise than high‑end cameras. Scanned images may
have image noise caused by the scanning sensor. Often, the film’s
grain pattern appears in the scanned image.</p>
<p>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. </p>
<p>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 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.</p>
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<ol><li class="stepexpand"><span>Choose
Filter&#160;&gt; Noise&#160;&gt; Reduce Noise.</span></li>
<li class="stepexpand"><span>Zoom in on the preview image to get a better view of
image noise.</span></li>
<li class="stepexpand"><span>Set options:</span> <dl><dt class="dlterm">Strength</dt>
<dd>Controls the amount of luminance noise reduction applied
to all image channels.</dd><p class="dlseparator"></p><dt class="dlterm">Preserve Details</dt>
<dd>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.</dd><p class="dlseparator"></p><dt class="dlterm">Reduce Color Noise</dt>
<dd>Removes random color pixels. A higher value reduces more
color noise.</dd><p class="dlseparator"></p><dt class="dlterm">Sharpen Details</dt>
<dd>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.</dd><p class="dlseparator"></p><dt class="dlterm">Remove JPEG Artifacts</dt>
<dd>Removes blocky image artifacts and halos caused by saving
a image using a low JPEG quality setting.</dd><p class="dlseparator"></p></dl>
</li>
<li class="stepexpand"><span>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.</span></li>
</ol>
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