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     <a href="WSB5D75388-8DC6-4c2d-B274-D311CE624673a.html"><b>Adjusting image sharpness and blur</b></a> 
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                <h1>
                    Add lens blur
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                <div><div class="section"><p>Adds blur to an image to give the effect
of a narrower depth of field so that some objects in the image stay
in focus and others areas are blurred. You can use a simple selection
to determine which areas are blurred, or you can provide a separate
alpha channel <dfn class="term">depth map</dfn> to describe exactly how you
want the blur added. </p>
<p>The Lens Blur filter uses the depth
map to determine the position of pixels in an image. With a depth
map selected, you can also use the cross‑hair cursor to set the
starting point of a given blur. You can use alpha channels and layer
masks to create depth maps; black areas in an alpha channel are
treated as though they’re at the front of the photo, and white areas
are treated as if they’re far in the distance.</p>
<div class="tip"><img src="images/tip_help.png" />To
create a gradual blurring (none at the bottom to maximum at the
top), create a new alpha channel and apply a gradient so that the
channel is white at the top of the image and black at the bottom.
Then select the Lens Blur filter and choose the alpha channel from
the Source pop‑up menu. To change the direction of the gradient,
select the Invert check box.</div><p>The way the blur appears depends
on the iris shape you choose. Iris shapes are determined by the
number of blades they contain. You can change blades of an iris
by curving them (making them more circular) or rotating them. You
can also reduce or magnify the preview by clicking the minus button
or the plus button.</p>
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<ol><li class="stepexpand"><span>Choose Filter&#160;&gt; Blur&#160;&gt;
Lens Blur.</span></li>
<li class="stepexpand"><span>For Preview, Choose Faster to generate quicker previews.
Choose More Accurate to view the final version of the image. More
Accurate previews take longer to generate.</span></li>
<li class="stepexpand"><span>For Depth Map, choose a source (if you have one) from
the Source pop‑up menu. Drag the Blur Focal Distance slider to set
the depth at which pixels are in focus. For example, if you set
focal distance to 100, pixels at 1 and at 255 are completely blurred,
and pixels closer to 100 are blurred less. If you click in the preview
image, the Blur Focal Distance slider changes to reflect the clicked location
and brings the depth of the clicked location into focus.</span></li>
<li class="stepexpand"><span>To invert the selection or alpha channel you’re using
as the depth map source, select Invert.</span></li>
<li class="stepexpand"><span>Choose an iris from the Shape pop‑up menu. If you wish,
drag the Blade Curvature slider to smooth the edges of the iris,
or drag the Rotation slider to rotate it. To add more blur, drag
the Radius slider.</span></li>
<li class="stepexpand"><span>For Specular Highlight, drag the Threshold slider to
select a brightness cutoff; all pixels brighter than the cutoff
value are treated as specular highlights. To increase the brightness
of the highlights, drag the Brightness slider.</span></li>
<li class="stepexpand"><span>To add noise to an image, choose Uniform or Gaussian.
To add noise without affecting color. choose Monochromatic. Drag
the Amount slider to increase or decrease noise.</span> <div class="tip"><img src="images/tip_help.png" />Blurring removes film grain and noise from
the original image. To make the image look realistic and unretouched,
you can return some of the removed noise to the image.</div></li>
<li class="stepexpand"><span>Click OK to apply the changes to your image.</span></li>
</ol>
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