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Applies histogram equalization to a field.


equalized = Equalize(data, bins, min, max, ihist, ohist);


Name Type Default Description
data scalar field none data to be equalized
bins integer input dependent number of equalization bins
min scalar or field min of data lower bound of equalization
max scalar or field max of data upper bound of equalization
ihist field histogram of data input distribution
ohist field uniform distribution output distribution


Name Type Description
equalized scalar field histogram-equalized data

Functional Details

This module equalizes an input data field so that the histogram of the output approximates a specified distribution (ohist), which by default is a uniform distribution.

If data specifies a series, the histogram of the entire series is used to construct the probability distribution, which is then applied to each field in the series.


is the scalar data field to be equalized.


is the number of bins to be used in creating the equalization histogram. The default value is 100, unless data consists of byte values. In that case, the default is: max - min + 1

min  and  max

specify the range of the data values to be equalized. Values outside that range remain unchanged.


  1. If neither parameter is specified, the values used are the minimum and maximum of the input field.

  2. If min is a scalar value, it is the minimum value equalized.

  3. If min is a data field, the minimum data value of that field is used.

  4. max is similarly interpreted.

  5. If min is a data field and max is unspecified, the module uses the minimum and maximum values of that field.


is the histogram used to determine the equalization function required, and by default it is the histogram of data. If ihist is specified explicitly and the number of bins specified does not match the number in the histogram, the module resamples the histogram so that it contains the specified number.


is the type of output histogram desired. By default, the module equalizes to a uniform distribution. You can equalize to some other distribution by specifying an appropriate histogram for this parameter.

Note: A well-formed histogram (for ihist and ohist) consists of a field with a "positions" component that defines the bins of the histogram; a "connections" component that connects the positions; and a "data" component that contains the number of items in each bin. The data should be connection dependent ("dep" "connections").


Equalize modifies the data component. All other components are unmodified.

Example Visual Programs


See Also

 Filter,  Morph,  Histogram

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