F_VN_Histogram

Calculate the (multi-channel) histogram of an image.
Can use available TwinCAT Job Tasks for executing parallel code regions.

Syntax

Definition:

FUNCTION F_VN_Histogram : HRESULT
VAR_INPUT
    ipSrcImage      : ITcVnImage;
    ipDestHistogram : Reference To  ITcVnContainer;
    hrPrev          : HRESULT;
END_VAR

Inputs

Name	Type	Description
ipSrcImage	ITcVnImage	Source image
ipDestHistogram	Reference To ITcVnContainer	Returns a container with a multi-channel histogram, where every channel is represented as a vector of UDINT (ContainerType_Vector_Vector_UDINT. Non-zero interface pointers are reused.)
hrPrev	HRESULT	HRESULT indicating the result of previous operations (If SUCCEEDED(hrPrev) equals false, no operation is executed.)

Return value

HRESULT

Further information

The function F_VN_Histogram calculates the histogram of the input image channel by channel.

Parameter

Input image

The input image ipSrcImage can have any format.

Histogram

The calculated multichannel histogram is returned as a container ipDestHistogram of the type ContainerType_Vector_Vector_UDINT. Each sub-element corresponds to the histogram of one channel. Each container of the histogram is represented as a UDINT, which specifies the number of pixels belonging to the container.

Expert parameters

The expert version F_VN_HistogramExp contains additional parameters.

Application

The determination of the most frequently occurring pixel value in a grayscale image looks like this, for example:

VAR
    ipDestHistograms    :   ITcVnContainer;
    ipSingleHistogram   :   ITcVnContainer;
    nIndex              :   ULINT;
    ipIterator          :   ITcVnBidirectionalIterator;
END_VAR

hr := F_VN_Histogram(
    ipSrcImage      :=  ipImageIn,
    ipDestHistogram :=  ipHistograms,
    hrPrev          :=  hr
);
hr := F_VN_GetAt_ITcVnContainer(ipHistograms, ipSingleHistogram, 0, hr);
hr := F_VN_MaxElement(ipSingleHistogram, ipIterator, nIndex, hr);
// nIndex now contains the most frequent pixel value in ipImageIn.

Samples

Handling histograms

Required License

TC3 Vision Base

System Requirements

Development environment	Target platform	PLC libraries to include
TwinCAT V3.1.4024.54 or later	PC or CX (x64) with PL50, e.g. Intel 4-core Atom CPU	Tc3_Vision