Table Of Contents

Equalize (G Dataflow)

Last Modified: October 26, 2017

Produces a histogram equalization of an image.

This node redistributes the pixel values of an image to linearize the accumulated histogram. The precision of the node is dependent on the histogram precision and the number of classes used in the histogram.

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image src

Reference to the source image.

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image mask

8-bit image that specifies the region of the small image to be copied.

Only pixels in the image src image that correspond to a non-zero pixel in the mask image are copied. All other pixels keep their original values. The entire image is processed if image mask is not connected.

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image dst

Reference to the destination image.

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histogram report in

Input that computes the equalization.

If this input is not connected, the node computes the histogram from the input source image to equalize the image. The cluster contains the following elements:

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histogram

Values in the array.

The elements found in this array are the number of pixels per class. The nth class contains all pixel values belonging to the interval [(starting value + (n ? 1) × interval width), (starting value + n × (interval width ? 1))].

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minimal value

Smallest pixel value used in calculating the histogram.

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maximal value

Largest pixel value used in calculating the histogram.

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starting value

Smallest pixel value from the first class calculated in the histogram.

starting value can be equal to the minimum value from the interval range or the smallest value found for the image type connected.

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interval width

Length of each class.

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mean value

Mean value of the pixels used in calculating the histogram.

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standard variation

Standard deviation of the histogram.

A higher value corresponds to a better distribution of the values in the histogram and the image.

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area (pixels)

Number of pixels used in the histogram calculation.

area (pixels) is influenced by the values specified in interval range and the contents of image mask.

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error in

Error conditions that occur before this node runs.

The node responds to this input according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Default: No error

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range

Cluster containing the minimum and maximum values for the range of pixel values to equalize.

If you do not connect this cluster or you keep the default values of (0,0), the node considers minimal value and maximal value of histogram report in to be the minimum and maximum values to equalize, and the node equalizes the entire image.

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minimum

Smallest value used for processing.

After processing, all pixel values that are less than or equal to the minimum in the original image are set to 0 for an 8-bit image. In 16-bit and floating-point images, these pixel values are set to the smallest pixel value found in the original image.

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maximum

Largest value used for processing.

After processing, all pixel values that are greater than or equal to the maximum in the original image are set to 255 for an 8-bit image. In 16-bit and floating-point images, these pixel values are set to the largest pixel value found in the original image.

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image dst out

Reference to the destination image.

If image dst is connected, image dst out is the same as image dst. Otherwise, image dst out refers to the image referenced by image.

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error out

Error information.

The node produces this output according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Equalizing an Image

Use the histogram report in input to equalize an image based on its histogram. To equalize a source image based on the histogram of another image, run the Histogram node before the Equalize node to supply an input for histogram report in.

Modification of the pixel value depends on the histogram contents, regardless of the image type used. All pixels entering into the same histogram class have an identical value after equalization.

Where This Node Can Run:

Desktop OS: Windows

FPGA: Not supported

Web Server: Not supported in VIs that run in a web application


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