This menu groups operations which filter images, or
which are filters in the photoshop sense.
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Convolution
- This
menu has several standard convolution operations
(blur, sharpen, edge detect, etc.), plus the option to
convolve with a custom kernel.
Two menu items are slightly more complicated.
Unsharp Mask transforms to CIE LAB colour space,
then sharpens just the L band with a cored unsharp
filter. The Tasks / Print menu has a version of this
filter tuned for typical inkjet printers.
Custom Blur builds and applies a square or gaussian
convolution kernel for you based on a radius
setting.
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Rank
- A preset median filter, and a custom rank filter
that lets you specify window size and rank.
The Image Rank item does pixel-wise ranking of a
set of images.
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Morphology
-
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.
The Threshold item does a simple level threshold.
Use the Math / Relational menu to construct more
complex image binarisations. Use Math / Boolean to
combine morphologies.
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.
See also Histogram / Find Profile for something
that can search an image for object edges. And
MathStatistics / Edges can count the number of edges
across and down an image.
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Fourier
- A selection of ideal, Gaussian and Butterworth
Fourier space filters.
You can make other mask shapes yourself using the
Image / Make Patterns menus, then apply them using
Math / Fourier. You can also use the image paintbox
to directly paint out peaks in a fourier-space image
before transforming back to real space.
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Enhance
- A selection of simple image enhancement
filters. Statistical Difference passes a window over an
image and tries to match the region statistics at
each point to a target mean and deviation.
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Spatial Correlation
- Place a small image at every possible
position in a big image and calculate the
correlation at each position. Simple Difference is the
much faster unnormalised version.
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GREYCstoration
- VIPS includes
a copy of the CImg library and you can use two
useful CImg operations from this menu: denoising
and enlarging.
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Tilt Brightness
- A selection of tools for adjusting the
brightness of an image across it’s surface. Useful
for correcting lighting problems.
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Blend
- 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.
One useful version is to use a text image (see Image
/ Make Patterns / Text) to blend between two colours
(see Colour / New).
Along Line does a left/right or top/bottom fade
between two images.
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Overlay
- Make a colour overlay of two monochrome
images. Useful with Image / Transform / for testing
image superposition.
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Colourize
- Use a colour image to tint a monochrome
image. Useful in conjunction with Image / Transform
/ .
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Browse
- Look at either the bits or the bands of an image.
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Photographic Negative and friends
- A small selection of
simple, faintly photoshop-style filters.