IMAQ Equalize VI

LabView NI Vision

IMAQ Equalize VI

Owning Palette: ProcessingInstalled With: NI Vision Development Module

Produces a histogram equalization of an image. This VI redistributes the pixel values of an image to linearize the accumulated histogram. The precision of the VI is dependent on the histogram precision, which in turn is dependent on the number of classes used in the histogram.

Details

IMAQ Equalize

Histogram Report is the histogram of an image that is used to compute the equalization. If this input is not connected, the VI computes the histogram from the source (input) image to equalize the image. The cluster contains the following elements:

	histogram returns the histogram values in an 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))].
	Minimal Value returns the smallest pixel value used in calculating the histogram.
	Maximal Value returns the largest pixel value used in calculating the histogram.
	Starting Value returns the smallest pixel value from the first class calculated in the histogram. It can be equal to the Minimum value from the Interval Range or the smallest value found for the image type connected.
	Interval Width returns the length of each class.
	Mean Value returns the mean value of the pixels used in calculating the histogram.
	Standard Variation returns the standard deviation from the histogram. A higher value corresponds to a better distribution of the values in the histogram and the image.
	Area (pixels) returns the number of pixels used in the histogram calculation. This is influenced by the values specified in Interval Range and the contents of Image Mask.

Image Src is a reference to the source image.

Image Mask is an 8-bit image that specifies the region of the small image that will be copied. Only those pixels in the Image Src (Small) image that correspond to an equivalent 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.

Image Dst is a reference to the destination image.

error in (no error) describes the error status before this VI or function runs. The default is no error. If an error occurred before this VI or function runs, the VI or function passes the error in value to error out. This VI or function runs normally only if no error occurred before this VI or function runs. If an error occurs while this VI or function runs, it runs normally and sets its own error status in error out. Use the Simple Error Handler or General Error Handler VIs to display the description of the error code. Use error in and error out to check errors and to specify execution order by wiring error out from one node to error in of the next node.

	status is TRUE (X) if an error occurred before this VI or function ran or FALSE (checkmark) to indicate a warning or that no error occurred before this VI or function ran. The default is FALSE.
	code is the error or warning code. If status is TRUE, code is a nonzero error code. If status is FALSE, code is 0 or a warning code.
	source describes the origin of the error or warning and is, in most cases, the name of the VI or function that produced the error or warning. The default is an empty string.

Range is a 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 VI considers Minimal Value and Maximal Value of Histogram Report to be the minimum and maximum values to equalize, and the VI equalizes the entire image.

	Minimum is the 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.
	Maximum is the 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.

Image Dst Out is a 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 Src.

error out contains error information. If error in indicates that an error occurred before this VI or function ran, error out contains the same error information. Otherwise, it describes the error status that this VI or function produces. Right-click the error out indicator on the front panel and select Explain Error from the shortcut menu for more information about the error.

	status is TRUE (X) if an error occurred or FALSE (checkmark) to indicate a warning or that no error occurred.
	code is the error or warning code. If status is TRUE, code is a nonzero error code. If status is FALSE, code is 0 or a warning code.
	source describes the origin of the error or warning and is, in most cases, the name of the VI or function that produced the error or warning. The default is an empty string.

Details

Use the optional Histogram Report input to equalize an image based on its histogram. To equalize a source image based on the histogram of another image, run the IMAQ Histogram VI before the IMAQ Equalize VI to supply an input for Histogram Report.

The modification to 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.

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