Calibration of linescan cameras

Enumerations
enum	CVFScanDirection { CVFSD_X = 0 , CVFSD_Y = 1 }

Functions
cvbres_t	CVFCreateLineScanCalibration (CVIPointD CalibrationPoint1, CVIPointD CalibrationPoint2, double ReferenceDistanceCalibrationPoints, int *ScanLineIndices, double *EdgeIndices, size_t NumScanLines, size_t NumEdgesPerScanLine, double ReferenceWidthStripes, const CVFLineScanCalibrationConfiguration &Configuration, NLTRANSFORMATION &Transformation, double &PixelSize, double &MeanError, double &StdDev)
	This function calibrates linescan cameras. More...
cvbres_t	CVFDetectEdgesOfStripeTarget (IMG ImageStripes, cvbdim_t Left, cvbdim_t Top, cvbdim_t Right, cvbdim_t Bottom, size_t NumStripes, CVFScanDirection ScanDirection, double Threshold, int *ScanLineIndices, double *EdgeIndices, size_t &NumScanLines, size_t &NumEdgesPerScanLine)
	This function detects edges from a calibration pattern with alternating black and white stripes. More...
cvbres_t	CVFGet2PointsForCalibrationOfMovement (IMG Image, cvbdim_t Index, const TArea &Aoi, TCalibrationPatternContrast Contrast, cvbval_t MinContrast, double MinPointSize, double MaxPointSize, CVFScanDirection ScanDirection, CVIPointD &FirstPoint, CVIPointD &SecondPoint)
	Extracts two points which can be used for the calibration of the movement of linescan cameras. If the image contains more than two points, the points which are nearest to the left and right edge (or top and bottom edge, if movement direction is x) are chosen. More...

Detailed Description

Enumeration Type Documentation

CVFScanDirection

enum CVFScanDirection

Enumeration for scanning direction of the camera.

Enumerator
CVFSD_X	The camera scans the target in X direction (movement of the camera is Y).
CVFSD_Y	The camera scans the target in Y direction (movement of the camera is X).

Function Documentation

CVFCreateLineScanCalibration()

cvbres_t CVFCreateLineScanCalibration	(	CVIPointD	CalibrationPoint1,
		CVIPointD	CalibrationPoint2,
		double	ReferenceDistanceCalibrationPoints,
		int *	ScanLineIndices,
		double *	EdgeIndices,
		size_t	NumScanLines,
		size_t	NumEdgesPerScanLine,
		double	ReferenceWidthStripes,
		const CVFLineScanCalibrationConfiguration &	Configuration,
		NLTRANSFORMATION &	Transformation,
		double &	PixelSize,
		double &	MeanError,
		double &	StdDev
	)

This function calibrates linescan cameras.

The transformation result includes a 3rd order polynom for the line calibration and a factor to correct the movement direction. Note, that x and y do not depend on each other. All mixed coefficients are zero.

For the calibration of the movement direction an image containing two calibration dots is needed. The pixel coordinates of the dots CalibrationPoint1 and CalibrationPoint2 are calculated by the function CVFGet2PointsForCalibrationOfMovement. CVFCreateLineScanCalibration needs these coordinates and the reference distance between the dots ReferenceDistanceCalibrationPoints.

For the linescan calibration an image of a pattern with alternating black and white stripes has to be aquired. Also, the width of the stripes ReferenceWidthStripes has to be given as reference. Function CVFDetectEdgesOfStripeTarget detects the stripes of the calibration pattern and gives their indices ScanLineIndices and EdgeIndices.

The resulting transformation can be applied to images using function CreateNLTransformedImage.

Parameters

[in]	CalibrationPoint1	First calibration point (left or top).
[in]	CalibrationPoint2	Second calibration point (right or bottom).
[in]	ReferenceDistanceCalibrationPoints	Reference distance between the two calibration points (same units as ReferenceWidthStripes).
[in]	ScanLineIndices	Array with scan line indices containing NumScanLines elements.
[in]	EdgeIndices	Array with edge indicies of each scan line containing NumScanLines x NumEdgesPerScanLine elements. The indices are stored scan line by scan line consecutively.
[in]	NumScanLines	Number of scan lines.
[in]	NumEdgesPerScanLine	Number of edges per scan line.
[in]	ReferenceWidthStripes	Reference width of stripes in calbration pattern ImageStripes (same units as ReferenceDistanceCalibrationPoints).
[in]	Configuration	Configuration of linescan calibration.
[out]	Transformation	Handle of result transformation object.
[out]	PixelSize	Pixel size after transformation (same units as ReferenceDistanceCalibrationPoints and ReferenceWidthStripes).
[out]	MeanError	Mean deviation of all distances between stripes of transformed image from reference stripe width.
[out]	StdDev	Standard deviation of MeanError.

Returns

One of the CVC_ERROR values. < 0 indicates an error.

See also

CVFGet2PointsForCalibrationOfMovement, CVFDetectEdgesOfStripeTarget, CreateNLTransformedImage

CVFDetectEdgesOfStripeTarget()

cvbres_t CVFDetectEdgesOfStripeTarget	(	IMG	ImageStripes,
		cvbdim_t	Left,
		cvbdim_t	Top,
		cvbdim_t	Right,
		cvbdim_t	Bottom,
		size_t	NumStripes,
		CVFScanDirection	ScanDirection,
		double	Threshold,
		int *	ScanLineIndices,
		double *	EdgeIndices,
		size_t &	NumScanLines,
		size_t &	NumEdgesPerScanLine
	)

This function detects edges from a calibration pattern with alternating black and white stripes.

The output of this function is used by function CVFCreateLineScanCalibration calculating the linescan calibration.

For the detection of the transition between the stripes, the CVB function CFindAllEdges is used. For further information see the documentation of the CVB edge tool.

Attention

If ScanDirection is X memory of size ImageHeigh(ImageStripes)*sizeof(int) bytes has to be allocated by the caller for ScanLineIndices and ImageHeight(ImageStripes)*sizeof(double)*(NumStripes + 1) for EdgeIndices. If ScanDirection is Y use ImageWidth(ImageStripes) instead of ImageHeight(ImageStripes). The scan line indices are stored in element 0 till NumScanLines in ScanLineIndices. In EdgesIndices the edges are stored line by line consecutively, NumEdgesScanLine for each line.

Parameters

[in]	ImageStripes	Calibration pattern with alternating black and white stripes.
[in]	Left	Left edge of area of interest for ImageStripes.
[in]	Top	Top edge of area of interest for ImageStripes.
[in]	Right	Right edge of area of interest for ImageStripes.
[in]	Bottom	Bottom edge of area of interest for ImageStripes.
[in]	NumStripes	Number of stripes in the calibration pattern.
[in]	ScanDirection	Scan direction of the camera.
[in]	Threshold	Threshold for edge detection in ImageStripes (pixel data type dependent, see also CFindAllEdges).
[out]	ScanLineIndices	Array to recive the indices of the scan lines.
[out]	EdgeIndices	Array to recive the indices of edges for each scan line.
[out]	NumScanLines	Number of scan lines where edges are correctly detected.
[out]	NumEdgesPerScanLine	Number of edges per scan line.

Returns

One of the CVC_ERROR values. < 0 indicates an error.

See also

CVFCreateLineScanCalibration, CVFGet2PointsForCalibrationOfMovement

CVFGet2PointsForCalibrationOfMovement()

cvbres_t CVFGet2PointsForCalibrationOfMovement	(	IMG	Image,
		cvbdim_t	Index,
		const TArea &	Aoi,
		TCalibrationPatternContrast	Contrast,
		cvbval_t	MinContrast,
		double	MinPointSize,
		double	MaxPointSize,
		CVFScanDirection	ScanDirection,
		CVIPointD &	FirstPoint,
		CVIPointD &	SecondPoint
	)

Extracts two points which can be used for the calibration of the movement of linescan cameras. If the image contains more than two points, the points which are nearest to the left and right edge (or top and bottom edge, if movement direction is x) are chosen.

Parameters

[in]	Image	Image containing the calibration points.
[in]	Index	Index of the plane to be processed.
[in]	Aoi	Area of interest where the calibration points can be found.
[in]	Contrast	Selects whether the image shows white on black or black on white dots.
[in]	MinContrast	Minimum gray value contrast between the object and the background of the calibration points. Value to be set depends on the quality of the image taken.
[in]	MinPointSize	Desired minimum point size (in number of pixels).
[in]	MaxPointSize	Desired maximum point size (in number of pixels).
[in]	ScanDirection	Scan direction of the camera.
[out]	FirstPoint	X and Y coordinate of top calibration point if ScanDirection is X, otherwise left point.
[out]	SecondPoint	X and Y coordinate of bottom calibration point if ScanDirection is X, otherwise right point.

Returns

One of the CVC_ERROR values. < 0 indicates an error.

See also

CVFCreateLineScanCalibration