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<h3 class="sectionHead"><span class="titlemark">5.2 </span> <a
id="x24-460005.2"></a>Filter</h3>
<!--l. 166--><p class="noindent" ><a name="nip_label_sec:menu-filter"></a>
<!--l. 168--><p class="indent" > This menu groups operations which filter images, or
which are filters in the photoshop sense.
<dl class="description"><dt class="description">
<span
class="phvb7t-x-x-80">Convolution</span> </dt><dd
class="description">This
menu has several standard convolution operations
(blur, sharpen, edge detect, etc.), plus the option to
convolve with a custom kernel.
<!--l. 177--><p class="noindent" >Two menu items are slightly more complicated.
<span
class="phvr7t-x-x-80">Unsharp Mask </span>transforms to CIE LAB colour space,
then sharpens just the L band with a cored unsharp
filter. The <span
class="phvr7t-x-x-80">Tasks </span>/ <span
class="phvr7t-x-x-80">Print </span>menu has a version of this
filter tuned for typical inkjet printers.
<!--l. 182--><p class="noindent" ><span
class="phvr7t-x-x-80">Custom Blur </span>builds and applies a square or gaussian
convolution kernel for you based on a radius
setting.
</dd><dt class="description">
<span
class="phvb7t-x-x-80">Rank</span> </dt><dd
class="description">A preset median filter, and a custom rank filter
that lets you specify window size and rank.
<!--l. 189--><p class="noindent" >The <span
class="phvr7t-x-x-80">Image Rank </span>item does pixel-wise ranking of a
set of images.
</dd><dt class="description">
<span
class="phvb7t-x-x-80">Morphology</span> </dt><dd
class="description">
These menu items implement basic morphological
operations. Images are zero for background and
non-zero (usually 255) for object. Matricies are
shown as 0, 1 and * for background, object and
don’t-care.
<!--l. 196--><p class="noindent" >The <span
class="phvr7t-x-x-80">Threshold </span>item does a simple level threshold.
Use the <span
class="phvr7t-x-x-80">Math </span>/ <span
class="phvr7t-x-x-80">Relational </span>menu to construct more
complex image binarisations. Use <span
class="phvr7t-x-x-80">Math </span>/ <span
class="phvr7t-x-x-80">Boolean </span>to
combine morphologies.
<!--l. 200--><p class="noindent" >The first half of the menu lists simple erode
and dilate operations, 4- and 8-way connected.
The second half contains several useful compound
filters. <!--l. 204--><p class="noindent" >See also <span
class="phvr7t-x-x-80">Histogram </span>/ <span
class="phvr7t-x-x-80">Find Profile </span>for something
that can search an image for object edges. And
<span
class="phvr7t-x-x-80">MathStatistics </span>/ <span
class="phvr7t-x-x-80">Edges </span>can count the number of edges
across and down an image.
</dd><dt class="description">
<span
class="phvb7t-x-x-80">Fourier</span> </dt><dd
class="description">A selection of ideal, Gaussian and Butterworth
Fourier space filters.
<!--l. 212--><p class="noindent" >You can make other mask shapes yourself using the
<span
class="phvr7t-x-x-80">Image </span>/ <span
class="phvr7t-x-x-80">Make Patterns </span>menus, then apply them using
<span
class="phvr7t-x-x-80">Math </span>/ <span
class="phvr7t-x-x-80">Fourier</span>. You can also use the image paintbox
to directly paint out peaks in a fourier-space image
before transforming back to real space.
</dd><dt class="description">
<span
class="phvb7t-x-x-80">Enhance</span> </dt><dd
class="description">A selection of simple image enhancement
filters. <span
class="phvr7t-x-x-80">Statistical Difference </span>passes a window over an
image and tries to match the region statistics at
each point to a target mean and deviation.
</dd><dt class="description">
<span
class="phvb7t-x-x-80">Spatial Correlation</span> </dt><dd
class="description">Place a small image at every possible
position in a big image and calculate the
correlation at each position. <span
class="phvr7t-x-x-80">Simple Difference </span>is the
much faster unnormalised version.
</dd><dt class="description">
<span
class="phvb7t-x-x-80">GREYCstoration</span> </dt><dd
class="description">VIPS includes
a copy of the CImg library and you can use two
useful CImg operations from this menu: denoising
and enlarging.
</dd><dt class="description">
<span
class="phvb7t-x-x-80">Tilt Brightness</span> </dt><dd
class="description">A selection of tools for adjusting the
brightness of an image across it’s surface. Useful
for correcting lighting problems.
</dd><dt class="description">
<span
class="phvb7t-x-x-80">Blend</span> </dt><dd
class="description">Blend two objects together using either a third
object to control the blend at each point, or a slider
to set all points together. You can blend almost
anything with anything.
<!--l. 240--><p class="noindent" >One useful version is to use a text image (see <span
class="phvr7t-x-x-80">Image</span>
/ <span
class="phvr7t-x-x-80">Make Patterns </span>/ <span
class="phvr7t-x-x-80">Text</span>) to blend between two colours
(see <span
class="phvr7t-x-x-80">Colour </span>/ <span
class="phvr7t-x-x-80">New</span>).
<!--l. 244--><p class="noindent" ><span
class="phvr7t-x-x-80">Along Line </span>does a left/right or top/bottom fade
between two images.
</dd><dt class="description">
<span
class="phvb7t-x-x-80">Overlay</span> </dt><dd
class="description">Make a colour overlay of two monochrome
images. Useful with <span
class="phvr7t-x-x-80">Image </span>/ <span
class="phvr7t-x-x-80">Transform </span>/ for testing
image superposition.
</dd><dt class="description">
<span
class="phvb7t-x-x-80">Colourize</span> </dt><dd
class="description">Use a colour image to tint a monochrome
image. Useful in conjunction with <span
class="phvr7t-x-x-80">Image </span>/ <span
class="phvr7t-x-x-80">Transform</span>
/ .
</dd><dt class="description">
<span
class="phvb7t-x-x-80">Browse</span> </dt><dd
class="description">Look at either the bits or the bands of an image.
</dd><dt class="description">
<span
class="phvb7t-x-x-80">Photographic Negative </span><span
class="ptmb7t-">and friends</span> </dt><dd
class="description">A small selection of
simple, faintly photoshop-style filters.
</dd></dl>
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