auto_threshold — Segment an image using thresholds determined from its histogram.
auto_threshold segments a single-channel image using
multiple thresholding. First, the absolute histogram of the gray
values is determined. Then, relevant minima are extracted from the
histogram, which are used successively as parameters for a
thresholding operation. The thresholds used for byte images are 0,
255, and all minima extracted from the histogram (after the
histogram has been smoothed with a Gaussian filter with standard
Sigma). For each gray value interval one
region is generated. Thus, the number of regions is the number of
minima + 1. For uint2 images, the above procedure is used
analogously. However, here the highest threshold is 65535.
Furthermore, for uint2 images the value of
refers to a histogram with 256 values, although internally histograms
with a higher resolution are used. This is done to facilitate
switching between image types without having to change the parameter
Sigma. For float images the thresholds are the minimum and
maximum gray value in the image and all minima extracted from the
histogram. Here, the scaling of the parameter
to the original gray values of the image.
The larger the value of
Sigma is chosen,
the fewer regions will be extracted. This operator is useful if the
regions to be extracted exhibit similar gray values (homogeneous
→object (byte / uint2 / real)
Regions with gray values within the automatically determined intervals.
→(real / integer)
Sigma for the Gaussian smoothing of the histogram.
Default value: 2.0
Suggested values: 0.0, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0
Typical range of values:
Minimum increment: 0.01
Recommended increment: 0.3
Sigma >= 0.0
read_image (Image, 'fabrik') median_image (Image, Median, 'circle', 3, 'mirrored') auto_threshold (Median, Seg, 2.0) connection (Seg, Connected)