The following provides a basic methodology for using the
PatternMatching
step:
-
Load
or grab a model source image.
-
Define the model from the model source image.
-
Define a search
region from the model source image.
-
Optionally,
specify a range for angular search.
Matrox Design Assistant provides several parameters you can
adjust to get the required result. For each individual model, you
can:
-
Set the expected Number of occurrences of the
model.
-
Specify the minimum Acceptance score required to
count the candidate model as a match. The Acceptance is set as a
percentage, where a perfect match is 100 and no correlation is 0.
You should experiment to decide what a typical match score is for
your application.
The model source image will be used to define the search model.
The image should be captured under the best possible circumstances
in order to obtain good contrast and uniform illumination.
Matrox Design Assistant can only perform pattern matching
operations on 8-bit grayscale images.
For more information on loading or grabbing an image, see
Chapter 28: Acquisition.
The model source will be used to search for occurrences of a
pattern in an image. As such, the model should be unique and not
defined from a flat region where all pixel values are consistent
with no edges. Additionally, the model source image should be of
the best quality possible.
There are 2 types of models.
-
Normalized.
-
Circular Overscan.
Normalized models are the recommended model type and are used
when almost no rotation is expected. You can also specify a
discrete set of rotations, for example, every 90 degrees. For full
rotational search use the ModelFinder
step.
A circular overscan model is only suitable for very small models
if the border of pixels around the model is the same in the model
source image and in the target image. When a circular overscan
model is created, a set of models is extracted from rotated
versions of the model. For this reason a circular overscan model
cannot be created closer than 20% of its width from the edge of the
model source image. Circular overscan models tradeoff very high
memory usage against faster search at angles.
When creating a model using circular overscan, the overscan data
outside the Model ROI is also extracted from the source image. When
extracting a model, it should not be extracted from a region too
close to the edge of its source image. This will generate an error
because the circular overscan data extends beyond the boundaries of
the image. More information can be found in the
Reconfigure step overview section in
Chapter 56: Reconfigure step for additional limitations.
A model can be defined in 2 ways: you can interactively define
an area of the model source image to use as your model, or you can
automatically add a unique model.
To interactively define a model, perform the following:
-
Click on the
Add image model (
)
toolbar button in the
Project toolbar and choose to add a normalized model, or a
circular overscan model.
-
In the Display
view, define your area by specifying a rectangle with by
clicking and dragging. You can cancel defining by pressing the
Escape key.
-
The defined model is shown in the
Configuration pane. You can Edit, Rename, or Delete this model.
You can also automatically define a model. This will search for
the specified number of most-suitable unique areas and of the
specified dimensions, in the model's source image. This can be used
when there are no significant differences between the source and
target images. For each area found, a model is automatically added.
Perform the following to add an automatic model:
-
Click on Add auto
model(s) in the
Configuration pane.
-
Specify the Number of models to search
and the Model
type.
-
You can set the Allocation mode to
Fast or
Best.
Best will
allocate the models with high precision while Fast will allocate the
models at high-speed.
-
Use Fast if
your model source image is large and Best if it is small.
-
Size X and
Size Y define
the width and height of the models.
-
Position
uncertainty X and Position uncertainty Y will
select models that are far enough from the image borders to be
present in the target images in the horizontal and vertical
direction respectively.
-
By default, models will be searched in the whole image.
-
In certain circumstances, models can be searched at angles. For
more information, see the PatternMatching step
advanced settings section later in this chapter.
The default search region is the whole image. To speed up the
search, you can define a search region. To do so, perform the
following:
-
At the bottom of the model's
Configuration pane, click on Search region.... You can
create a new search rectangle or link to an existing shape in
another step. Also, you can edit the shape and its fixture in the
Configuration pane or interactively. For more information,
see the
Search regions section in
Chapter 2: Building a project.
-
If you want the region to be fixtured, set its coordinate
system. It is set to the Absolute coordinate system
by default.
-
Define the region interactively by clicking the Redefine button and clicking
and dragging on the image itself, or explicitly by entering exact
values in the
Configuration pane.
The search region must be large enough to contain all expected
occurrences of a model's Reference Point, but does not need to
contain the entire model.