lsd.h File Reference

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Functions
double *	LineSegmentDetection (int *n_out, double *img, int X, int Y, double scale, double sigma_scale, double quant, double ang_th, double log_eps, double density_th, int n_bins, int **reg_img, int *reg_x, int *reg_y)
double *	lsd_scale_region (int *n_out, double *img, int X, int Y, double scale, int **reg_img, int *reg_x, int *reg_y)
double *	lsd_scale (int *n_out, double *img, int X, int Y, double scale)
double *	lsd (int *n_out, double *img, int X, int Y)

Detailed Description

LSD module header

Author

rafael grompone von gioi gromp.nosp@m.one@.nosp@m.gmail.nosp@m..com

Definition in file lsd.h.

Function Documentation

LineSegmentDetection()

double* LineSegmentDetection	(	int *	n_out,
		double *	img,
		int	X,
		int	Y,
		double	scale,
		double	sigma_scale,
		double	quant,
		double	ang_th,
		double	log_eps,
		double	density_th,
		int	n_bins,
		int **	reg_img,
		int *	reg_x,
		int *	reg_y
	)

LSD Full Interface

Parameters

n_out	Pointer to an int where LSD will store the number of line segments detected.
img	Pointer to input image data. It must be an array of doubles of size X x Y, and the pixel at coordinates (x,y) is obtained by img[x+y*X].
X	X size of the image: the number of columns.
Y	Y size of the image: the number of rows.
scale	When different from 1.0, LSD will scale the input image by 'scale' factor by Gaussian filtering, before detecting line segments. Example: if scale=0.8, the input image will be subsampled to 80% of its size, before the line segment detector is applied. Suggested value: 0.8
sigma_scale	When scale!=1.0, the sigma of the Gaussian filter is: sigma = sigma_scale / scale, if scale < 1.0 sigma = sigma_scale, if scale >= 1.0 Suggested value: 0.6
quant	Bound to the quantization error on the gradient norm. Example: if gray levels are quantized to integer steps, the gradient (computed by finite differences) error due to quantization will be bounded by 2.0, as the worst case is when the error are 1 and -1, that gives an error of 2.0. Suggested value: 2.0
ang_th	Gradient angle tolerance in the region growing algorithm, in degrees. Suggested value: 22.5
log_eps	Detection threshold, accept if -log10(NFA) > log_eps. The larger the value, the more strict the detector is, and will result in less detections. (Note that the 'minus sign' makes that this behavior is opposite to the one of NFA.) The value -log10(NFA) is equivalent but more intuitive than NFA: -1.0 gives an average of 10 false detections on noise 0.0 gives an average of 1 false detections on noise 1.0 gives an average of 0.1 false detections on nose 2.0 gives an average of 0.01 false detections on noise

Suggested value: 0.0

Parameters

density_th	Minimal proportion of 'supporting' points in a rectangle. Suggested value: 0.7
n_bins	Number of bins used in the pseudo-ordering of gradient modulus. Suggested value: 1024
reg_img	Optional output: if desired, LSD will return an int image where each pixel indicates the line segment to which it belongs. Unused pixels have the value '0', while the used ones have the number of the line segment, numbered 1,2,3,..., in the same order as in the output list. If desired, a non NULL int** pointer must be assigned, and LSD will make that the pointer point to an int array of size reg_x x reg_y, where the pixel value at (x,y) is obtained with (*reg_img)[x+y*reg_x]. Note that the resulting image has the size of the image used for the processing, that is, the size of the input image scaled by the given factor 'scale'. If scale!=1 this size differs from XxY and that is the reason why its value is given by reg_x and reg_y. Suggested value: NULL
reg_x	Pointer to an int where LSD will put the X size 'reg_img' image, when asked for. Suggested value: NULL
reg_y	Pointer to an int where LSD will put the Y size 'reg_img' image, when asked for. Suggested value: NULL

Returns

A double array of size 7 x n_out, containing the list of line segments detected. The array contains first 7 values of line segment number 1, then the 7 values of line segment number 2, and so on, and it finish by the 7 values of line segment number n_out. The seven values are:

• x1,y1,x2,y2,width,p,-log10(NFA)

for a line segment from coordinates (x1,y1) to (x2,y2), a width 'width', an angle precision of p in (0,1) given by angle_tolerance/180 degree, and NFA value 'NFA'. If 'out' is the returned pointer, the 7 values of line segment number 'n+1' are obtained with 'out[7*n+0]' to 'out[7*n+6]'.

LSD full interface.

Definition at line 2025 of file lsd.c.

References image.

Referenced by lsd_scale_region().

lsd()

double* lsd	(	int *	n_out,
		double *	img,
		int	X,
		int	Y
	)

LSD Simple Interface

Parameters

n_out	Pointer to an int where LSD will store the number of line segments detected.
img	Pointer to input image data. It must be an array of doubles of size X x Y, and the pixel at coordinates (x,y) is obtained by img[x+y*X].
X	X size of the image: the number of columns.
Y	Y size of the image: the number of rows.

Returns

A double array of size 7 x n_out, containing the list of line segments detected. The array contains first 7 values of line segment number 1, then the 7 values of line segment number 2, and so on, and it finish by the 7 values of line segment number n_out. The seven values are:

• x1,y1,x2,y2,width,p,-log10(NFA)

for a line segment from coordinates (x1,y1) to (x2,y2), a width 'width', an angle precision of p in (0,1) given by angle_tolerance/180 degree, and NFA value 'NFA'. If 'out' is the returned pointer, the 7 values of line segment number 'n+1' are obtained with 'out[7*n+0]' to 'out[7*n+6]'.

LSD Simple Interface.

Definition at line 2243 of file lsd.c.

References lsd_scale(), and X.

lsd_scale()

double* lsd_scale	(	int *	n_out,
		double *	img,
		int	X,
		int	Y,
		double	scale
	)

LSD Simple Interface with Scale

Parameters

n_out	Pointer to an int where LSD will store the number of line segments detected.
img	Pointer to input image data. It must be an array of doubles of size X x Y, and the pixel at coordinates (x,y) is obtained by img[x+y*X].
X	X size of the image: the number of columns.
Y	Y size of the image: the number of rows.
scale	When different from 1.0, LSD will scale the input image by 'scale' factor by Gaussian filtering, before detecting line segments. Example: if scale=0.8, the input image will be subsampled to 80% of its size, before the line segment detector is applied. Suggested value: 0.8

Returns

A double array of size 7 x n_out, containing the list of line segments detected. The array contains first 7 values of line segment number 1, then the 7 values of line segment number 2, and so on, and it finish by the 7 values of line segment number n_out. The seven values are:

• x1,y1,x2,y2,width,p,-log10(NFA)

for a line segment from coordinates (x1,y1) to (x2,y2), a width 'width', an angle precision of p in (0,1) given by angle_tolerance/180 degree, and NFA value 'NFA'. If 'out' is the returned pointer, the 7 values of line segment number 'n+1' are obtained with 'out[7*n+0]' to 'out[7*n+6]'.

LSD Simple Interface with Scale.

Definition at line 2235 of file lsd.c.

References lsd_scale_region(), NULL, and X.

Referenced by lsd().

lsd_scale_region()

double* lsd_scale_region	(	int *	n_out,
		double *	img,
		int	X,
		int	Y,
		double	scale,
		int **	reg_img,
		int *	reg_x,
		int *	reg_y
	)

LSD Simple Interface with Scale and Region output.

Parameters

n_out	Pointer to an int where LSD will store the number of line segments detected.
img	Pointer to input image data. It must be an array of doubles of size X x Y, and the pixel at coordinates (x,y) is obtained by img[x+y*X].
X	X size of the image: the number of columns.
Y	Y size of the image: the number of rows.
scale	When different from 1.0, LSD will scale the input image by 'scale' factor by Gaussian filtering, before detecting line segments. Example: if scale=0.8, the input image will be subsampled to 80% of its size, before the line segment detector is applied. Suggested value: 0.8
reg_img	Optional output: if desired, LSD will return an int image where each pixel indicates the line segment to which it belongs. Unused pixels have the value '0', while the used ones have the number of the line segment, numbered 1,2,3,..., in the same order as in the output list. If desired, a non NULL int** pointer must be assigned, and LSD will make that the pointer point to an int array of size reg_x x reg_y, where the pixel value at (x,y) is obtained with (*reg_img)[x+y*reg_x]. Note that the resulting image has the size of the image used for the processing, that is, the size of the input image scaled by the given factor 'scale'. If scale!=1 this size differs from XxY and that is the reason why its value is given by reg_x and reg_y. Suggested value: NULL
reg_x	Pointer to an int where LSD will put the X size 'reg_img' image, when asked for. Suggested value: NULL
reg_y	Pointer to an int where LSD will put the Y size 'reg_img' image, when asked for. Suggested value: NULL

Returns

A double array of size 7 x n_out, containing the list of line segments detected. The array contains first 7 values of line segment number 1, then the 7 values of line segment number 2, and so on, and it finish by the 7 values of line segment number n_out. The seven values are:

• x1,y1,x2,y2,width,p,-log10(NFA)

for a line segment from coordinates (x1,y1) to (x2,y2), a width 'width', an angle precision of p in (0,1) given by angle_tolerance/180 degree, and NFA value 'NFA'. If 'out' is the returned pointer, the 7 values of line segment number 'n+1' are obtained with 'out[7*n+0]' to 'out[7*n+6]'.

LSD Simple Interface with Scale and Region output.

Definition at line 2212 of file lsd.c.

References LineSegmentDetection(), G3Point::quant(), and X.

Referenced by lsd_scale().