| Operators |
segment_image_mser — Segment image using Maximally Stable Extremal Regions (MSER).
segment_image_mser(Image : MSERDark, MSERLight : Polarity, MinArea, MaxArea, Delta, GenParamName, GenParamValue : )
segment_image_mser segments an image into regions of homogenous gray values using the approach of Maximally Stable Extremal Regions (MSER). The segmentation process determines if a region is homogenous by observing the local region surrounding. Therefore, the operator is particularly suited to robustly segment objects in front of inhomogeneous background or in applications with changing illumination.
Parameters
The Polarity determines the type of the regions that are extracted.
| Value | Meaning |
|---|---|
| 'dark' | Only MSERs that are darker than their surroundings are extracted |
| 'light' | Only MSERs that are lighter than their surroundings are extracted |
| 'both' (default) | Both types of MSERs are extracted |
The values MinArea and MaxArea restrict the size of the returned MSERs.
Note that very small values of MinArea, e.g., values smaller than 5, can increase the runtime significantly, especially for noisy images.
To deactivate the restriction for the maximum area of the returned MSERs, set MaxArea to an empty tuple (which is the default).
The value of Delta influences the selectivity of the algorithm. Larger values lead to fewer MSERs. Smaller values lead to more MSERs.
Please read the description of the segmentation process below to help understand the effect of this parameter.
The following generic parameters can be used to fine-tune the segmentation of MSERs. The generic parameters can be set with GenParamName and GenParamValue.
The maximum variation of a component's area within the range of Delta thresholds. Larger values lead to more MSERs. Smaller values lead to fewer MSERs.
Please read the description of the segmentation process below for a definition of 'variation' and to help understand the effect of this generic parameter.
Values: real values larger than or equal to 0.0
Suggested values: 0.1, 0.2, 0.5, 1.0, 2.0, 5.0
Default: 0.2
The minimum relative difference of the sizes of two overlapping MSERs. Smaller values lead to more overlapping MSERs. Larger values lead to fewer overlapping MSERs.
Please read the description of the segmentation process below for a definition of 'diversity' and to help understand the effect of this generic parameter.
Setting 'min_diversity' very close to 0.0 may increase the runtime.
Values: real values larger than or equal to 0.0
Suggested values: 0.1, 0.5, 0.8, 1.0, 2.0, 5.0
Default: 0.8
Controls if regions that touch the border of the input domain are returned ('true') or rejected ('false').
Values: 'false', 'true'
Default: 'false'
Segmentation Process
In a first step, the image is segmented with all threshold values t, from 0 to the maximal present gray value.
To illustrate this, the following example input image with twelve gray values (0...11) is used. On the right, the boundaries of the resulting threshold regions are shown.
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Example input image with twelve gray values reaching from 0 (= black) to 11 (= white)
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Boundaries of the threshold regions for all thresholds (t = 0...11)
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The resulting threshold regions are split into their connected components (4-connected neighborhood) and the area increase of the individual components is monitored over the increasing thresholds. The area of each individual component increases monotonically with each (increasing) threshold. An MSER is a component whose area does not vary significantly within the range of Delta thresholds. To be accepted as an MSER, the variation of the component's area within the range of Delta thresholds must be a local minimum and it must be lower than 'max_variation'. Furthermore, the diversity of overlapping MSERs must be greater than 'min_diversity' (see below).
The variation of a component's area is defined by
Decreasing the value of 'max_variation' will reduce the number of accepted regions.
In our example, each threshold region consists of only one component. Therefore, the terms 'threshold region' and 'component' are used synonymously hereinafter. The following table shows the area of the threshold regions and their variations for Delta set to 1 and for Delta set to 2.