This menu groups operations which filter images, or
which are filters in the photoshop sense.
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.
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.
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.
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.
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.
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.
GREYCstoration
VIPS includes
a copy of the CImg library and you can use two
useful CImg operations from this menu: denoising
and enlarging.
Tilt Brightness
A selection of tools for adjusting the
brightness of an image across it’s surface. Useful
for correcting lighting problems.
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.
Overlay
Make a colour overlay of two monochrome
images. Useful with Image / Transform / for testing
image superposition.
Colourize
Use a colour image to tint a monochrome
image. Useful in conjunction with Image / Transform
/ .
Browse
Look at either the bits or the bands of an image.
Photographic Negative and friends
A small selection of
simple, faintly photoshop-style filters.