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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="pcrb7t-">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="pcrr7t-">Unsharp Mask </span>transforms to CIE LAB colour
space, then sharpens just the L band with a cored
unsharp filter. The <span
class="pcrr7t-">Tasks </span>/ <span
class="pcrr7t-">Print </span>menu has
a version of this filter tuned for typical inkjet
printers.
<!--l. 182--><p class="noindent" ><span
class="pcrr7t-">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="pcrb7t-">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="pcrr7t-">Image Rank </span>item does pixel-wise ranking
of a set of images.
</dd><dt class="description">
<span
class="pcrb7t-">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="pcrr7t-">Threshold </span>item does a simple level
threshold. Use the <span
class="pcrr7t-">Math </span>/ <span
class="pcrr7t-">Relational </span>menu to
construct more complex image binarisations. Use
<span
class="pcrr7t-">Math </span>/ <span
class="pcrr7t-">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="pcrr7t-">Histogram </span>/ <span
class="pcrr7t-">Find Profile </span>for
something that can search an image for object
edges. And <span
class="pcrr7t-">MathStatistics </span>/ <span
class="pcrr7t-">Edges </span>can
count the number of edges across and down an
image.
</dd><dt class="description">
<span
class="pcrb7t-">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="pcrr7t-">Image </span>/ <span
class="pcrr7t-">Make Patterns </span>menus, then apply
them using <span
class="pcrr7t-">Math </span>/ <span
class="pcrr7t-">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="pcrb7t-">Enhance</span> </dt><dd
class="description">A selection of simple image enhancement
filters. <span
class="pcrr7t-">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="pcrb7t-">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="pcrr7t-">Simple</span>
<span
class="pcrr7t-">Difference </span>is the much faster unnormalised
version.
</dd><dt class="description">
<span
class="pcrb7t-">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="pcrb7t-">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="pcrb7t-">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="pcrr7t-">Image </span>/ <span
class="pcrr7t-">Make Patterns </span>/ <span
class="pcrr7t-">Text</span>) to blend
between two colours (see <span
class="pcrr7t-">Colour </span>/ <span
class="pcrr7t-">New</span>).
<!--l. 244--><p class="noindent" ><span
class="pcrr7t-">Along Line </span>does a left/right or top/bottom fade
between two images.
</dd><dt class="description">
<span
class="pcrb7t-">Overlay</span> </dt><dd
class="description">Make a colour overlay of two monochrome
images. Useful with <span
class="pcrr7t-">Image </span>/ <span
class="pcrr7t-">Transform </span>/ for
testing image superposition.
</dd><dt class="description">
<span
class="pcrb7t-">Colourize</span> </dt><dd
class="description">Use a colour image to tint a monochrome
image. Useful in conjunction with <span
class="pcrr7t-">Image </span>/
<span
class="pcrr7t-">Transform </span>/ .
</dd><dt class="description">
<span
class="pcrb7t-">Browse</span> </dt><dd
class="description">Look at either the bits or the bands of an
image.
</dd><dt class="description">
<span
class="pcrb7t-">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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