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Open eVision
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General Features
Development Tools
Open eVision Studio
Libraries
General-purpose
EasyImage
EasyColor
EasyObject
EasyMatch
EasyFind
EasyGauge
Mark Inspection
Open eVision
Data Sheet
Open eVision Eval
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Pattern Matching
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Main Features
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Typical Applications
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Normalized correlation method
Sub-pixel accuracy
Rotation and scaling support
Multiple pattern occurrences
Gray level and color images support
Non-square pixels management
Don't care areas
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Die & wire bonding
Fiducial alignment
Printing alignment
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EasyMatch is a gray-level and color pattern matching library. It lets you train the system on a reference pattern and afterwards locate
its occurrences in other images. This tool is very convenient when the position of a given part is unknown in the field of view, or if
the presence of parts must be controlled. EasyMatch works by using correlation, i.e. measuring discrepancies between the reference
pattern and the target image.
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Features
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Multiple pattern occurrences
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Several occurrences of a pattern, up to a user-defined number, are returned. Only the reliable ones are retained.
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Standard, offset-normalized, gain-normalized and fully normalized correlation
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The correlation is computed on continuous tone values (as opposed to binary).
It is well known that when the lighting conditions vary, as it is often the
case, straight comparison of the pattern and image behaves badly. To cope
with this, automatically adjusting the contrast and/or intensity of the pattern
before comparison is very effective. This process is known as normalization.
EasyMatch provides four distinct normalization modes, depending on
whether a gain and/or offset compensation is used.
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Normal, inverse or mixed contrast
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Because of particular lighting effects, an object can appear with inverted contrast (white on black instead of
black on white or conversely). Depending on the application, it can be useful to keep inverted instances or to
disregard them. Three matching modes are available: consider positive occurrences only, negative occurrences
only or both.
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Translation, rotation and isotropic/anisotropic scaling
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To find the best matches between the pattern and target image,
the target is allowed to translate horizontally and vertically. Additionally,
it can be allowed to rotate and/or to change its scale
in the X and Y directions simultaneously or independently. The
rotation angle and scale factors vary in a user-specified interval.
All degrees of freedom can be combined at will.
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Variable accuracy, up to sub-pixel level
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The accuracy with which the pattern is measured can be chosen
(the less accurate, the faster). A one tenth-of-a-pixel accuracy
can be achieved.
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Don't care pixels
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When the pattern cannot be inscribed in a rectangular ROI, the surrounding of
the pattern can be ignored by setting the pixels values below a threshold level.
These pixels will not take part in the matching process. The same feature can
be used if parts of the template change from sample to sample.
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Gray-level and color images
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EasyMatch processes 8-bit grayscale images as well as 24-bit RGB images.
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Non-square pixels
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When images are acquired with non-square pixels, rotated objects appear
skewed. Taking the pixel aspect ratio into account can compensate for this
effect.
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