IMAQ Histogram VI

LabView NI Vision

IMAQ Histogram VI

Owning Palette: AnalysisInstalled With: NI Vision Development Module

Calculates the histogram of an image.

IMAQ Histogram

Number of Classes specifies the number of classes used to classify the pixels. The number of obtained classes differs from the specified amount in a case in which the minimum and maximum boundaries are overshot in the Interval Range. It is advised to specify a number of classes that is a power of two (for example, 2, 4, or 8) for 8-bit or 16-bit images. The default value is 256, which is designed for 8-bit images. This value gives a uniform class distribution or one class for each grayscale intensity in an 8-bit image.

Image is a reference to the source image.

Image Mask is an 8-bit image specifying the region in the image to use for the calculation. Only those pixels in the original image that correspond to an equivalent non-zero pixel in the mask image are used for the calculation. The entire image is used in the calculation if Image Mask is not connected.

Interval Range is a cluster specifying the minimum and maximum boundaries for the histogram calculation. Only those pixels having a value that falls in this range are taken into account by the histogram calculation. This cluster is composed of the following elements:

Minimum is the minimum interval value. The default value of (0, 0) ensures that the real minimum value is determined by the source image, as described in the following table.

Image Type	Minimum Value Used
	0
	Minimum pixel value found in the image
	Minimum pixel value found in the image

Maximum is the maximum interval value. The default value of (0, 0) ensures that the real maximum value is determined by the source image, as described in the following table.

Image Type	Maximum Value Used
	0
	Maximum pixel value found in the image
	Maximum pixel value found in the 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.

Histogram Report is a cluster that returns the histogram values. This 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.

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.

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