Class SoAutoThresholdingProcessing
- java.lang.Object
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- com.openinventor.inventor.Inventor
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- com.openinventor.inventor.misc.SoBase
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- com.openinventor.inventor.fields.SoFieldContainer
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- com.openinventor.inventor.engines.SoEngine
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- com.openinventor.imageviz.engines.SoImageVizEngine
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- com.openinventor.imageviz.engines.imagesegmentation.binarization.SoAutoThresholdingProcessing
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- All Implemented Interfaces:
SafeDisposable
public class SoAutoThresholdingProcessing extends SoImageVizEngine
SoAutoThresholdingProcessing
engine. TheSoAutoThresholdingProcessing
engine computes an automatic threshold on a gray level image.This engine computes an automatic threshold on a grayscale image i.e. separate the image in 2 classes of pixels. Three methods of classification are available: Entropy, Factorisation or Moments. The computed threshold is provided in the
SbAutoThresholdingDetail
object.Entropy
The entropy principle defines 2 classes in the image histogram by minimizing the total classes' entropy, for more theory the reader can refers to references [1] and [2]. Considering the first-order probability histogram of an image and assuming that all symbols in the flowing equation are statistically independent, its entropy (in the Shannon sense) is defined as:Where is the number of grayscales, the probability of occurrence of level and is the log in base 2.
Let us denote the value of the threshold and the search interval. We can define two partial entropies:
Where defines the probability of occurrence of level in the range and defines the probability of occurrence of level in the range [t+1,I2]. We search the threshold value which minimizes the sum :
Figure 1: Example of thresholding using the entropy method Factorization
The factorization method is based on the Otsu criterion (see [3] for details), i.e. minimizing the within-class variance:Where and are respectively the probabilities occurrence and , the variances of classes and .
A faster and equivalent approach is to maximize the between-class variance:
The within-class variance calculation is based on the second-order statistics (variances) while the between-class variance calculation is based on the first order statistics (means). It is therefore simplest and faster to use this last optimization criterion. We then search the value which maximizes the between-class variance such as:
Figure 2: Example of thresholding using the factorization method Moments
The momentSoAutoThresholdingProcessing
uses the moment-preserving bi-level thresholding described by W.H.Tsai in [4]. Moments of an image can be computed from its histogram in the following way:Where is the probability of occurrence of grayscale . For the following we note the original grayscale image and the threshold image. Image can be considered as a blurred version of an ideal bi-level image which consists of pixels with only two gray values: and . The moment-preserving thresholding principle is to select a threshold value such that if all below-threshold gray values of the original image are replaced by and all above threshold gray values replaced by , then the first three moments of the original image are preserved in the resulting bi-level image. Image so obtained may be regarded as an ideal unblurred version of . Let and denote the fractions of the below-threshold pixels and the above-threshold pixels in , respectively, then the first three moments of are:
And preserving the first three moments in , means the equalities:
To find the desired threshold value , we can first solve the four equations system to obtain and , and then choose as the -tile of the histogram of . Note that and will also be obtained simultaneously as part of the solutions of system.
Figure 3: Example of thresholding using the moment-preserving method [1] T.Pun, Entropic thresholding: A new approach, comput. Graphics Image Process. 16, 1981, 210-239
[2] J. N. Kapur, P. K. Sahoo, and A. K. C. Wong, "A New Method for Gray-Level Picture Thresholding Using the Entropy of the Histogram" Computer Vision, Graphics and Image Processing 29, pp. 273-285, Mar. 1985
[3] Otsu, N. 1979. A thresholding selection method from grayscale histogram. IEEE Transactions on Systems, Man, and Cybernetics9(1): 62-66
[4] Tsai, W. H. 1985. Moment-preserving thresholding: A New Approach. Computer Vision, Graphics, and Image Processing 29: 377-393
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Nested Class Summary
Nested Classes Modifier and Type Class Description static class
SoAutoThresholdingProcessing.ObjectLightnessType
static class
SoAutoThresholdingProcessing.RangeModes
static class
SoAutoThresholdingProcessing.SbAutoThresholdingDetail
Results details of threshold by automatic segmentation.static class
SoAutoThresholdingProcessing.ThresholdCriterions
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Nested classes/interfaces inherited from class com.openinventor.imageviz.engines.SoImageVizEngine
SoImageVizEngine.ComputeModes, SoImageVizEngine.EventArg, SoImageVizEngine.Neighborhood3ds
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Nested classes/interfaces inherited from class com.openinventor.inventor.Inventor
Inventor.ConstructorCommand
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Field Summary
Fields Modifier and Type Field Description SoSFEnum<SoImageVizEngine.ComputeModes>
computeMode
Select the compute Mode (2D or 3D or AUTO) .SoSFImageDataAdapter
inGrayImage
The input grayscale image.SoSFVec2f
intensityRangeInput
The input intensity range.SoSFEnum<SoAutoThresholdingProcessing.ObjectLightnessType>
objectLightness
Select the lightness mode for object to detect.SoImageVizEngineOutput<SoSFImageDataAdapter,SoImageDataAdapter>
outBinaryImage
The output binary image.SoImageVizEngineAnalysisOutput<SoAutoThresholdingProcessing.SbAutoThresholdingDetail>
outResult
The thresholding results.SoSFEnum<SoAutoThresholdingProcessing.RangeModes>
rangeMode
Select the input intensity range mode.SoSFEnum<SoAutoThresholdingProcessing.ThresholdCriterions>
thresholdCriterion
The criterion to detect thresholds on histogram.-
Fields inherited from class com.openinventor.imageviz.engines.SoImageVizEngine
onBegin, onEnd, onProgress
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Fields inherited from class com.openinventor.inventor.Inventor
VERBOSE_LEVEL, ZeroHandle
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Constructor Summary
Constructors Constructor Description SoAutoThresholdingProcessing()
Constructor.
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Method Summary
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Methods inherited from class com.openinventor.imageviz.engines.SoImageVizEngine
abortEvaluate, isEvaluating, startEvaluate, waitEvaluate
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Methods inherited from class com.openinventor.inventor.engines.SoEngine
copy, getByName, getOutput, getOutputName
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Methods inherited from class com.openinventor.inventor.fields.SoFieldContainer
copyFieldValues, copyFieldValues, enableNotify, fieldsAreEqual, get, getAllFields, getEventIn, getEventOut, getField, getFieldName, hasDefaultValues, isNotifyEnabled, set, setToDefaults
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Methods inherited from class com.openinventor.inventor.misc.SoBase
dispose, getName, isDisposable, isSynchronizable, setName, setSynchronizable, touch
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Methods inherited from class com.openinventor.inventor.Inventor
getNativeResourceHandle
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Field Detail
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computeMode
public final SoSFEnum<SoImageVizEngine.ComputeModes> computeMode
Select the compute Mode (2D or 3D or AUTO) . Default is MODE_AUTO
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objectLightness
public final SoSFEnum<SoAutoThresholdingProcessing.ObjectLightnessType> objectLightness
Select the lightness mode for object to detect. . Default is BRIGHT_OBJECTS
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inGrayImage
public final SoSFImageDataAdapter inGrayImage
The input grayscale image. Default value is NULL. Supported types include: grayscale image.
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intensityRangeInput
public final SoSFVec2f intensityRangeInput
The input intensity range. Default value isSbVec2f
(0.0f,255.0f).
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thresholdCriterion
public final SoSFEnum<SoAutoThresholdingProcessing.ThresholdCriterions> thresholdCriterion
The criterion to detect thresholds on histogram. . Default is ENTROPY
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rangeMode
public final SoSFEnum<SoAutoThresholdingProcessing.RangeModes> rangeMode
Select the input intensity range mode. . Default is MIN_MAX
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outBinaryImage
public final SoImageVizEngineOutput<SoSFImageDataAdapter,SoImageDataAdapter> outBinaryImage
The output binary image. Default value is NULL. Supported types include: binary image.
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outResult
public final SoImageVizEngineAnalysisOutput<SoAutoThresholdingProcessing.SbAutoThresholdingDetail> outResult
The thresholding results. Default value is NULL.
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