local_max_sub_pixT_local_max_sub_pixLocalMaxSubPixLocalMaxSubPixlocal_max_sub_pix (Operator)


local_max_sub_pixT_local_max_sub_pixLocalMaxSubPixLocalMaxSubPixlocal_max_sub_pix — Subpixel precise detection of local maxima in an image.


local_max_sub_pix(Image : : Filter, Sigma, Threshold : Row, Column)

Herror T_local_max_sub_pix(const Hobject Image, const Htuple Filter, const Htuple Sigma, const Htuple Threshold, Htuple* Row, Htuple* Column)

void LocalMaxSubPix(const HObject& Image, const HTuple& Filter, const HTuple& Sigma, const HTuple& Threshold, HTuple* Row, HTuple* Column)

void HImage::LocalMaxSubPix(const HString& Filter, double Sigma, double Threshold, HTuple* Row, HTuple* Column) const

void HImage::LocalMaxSubPix(const char* Filter, double Sigma, double Threshold, HTuple* Row, HTuple* Column) const

void HImage::LocalMaxSubPix(const wchar_t* Filter, double Sigma, double Threshold, HTuple* Row, HTuple* Column) const   (Windows only)

static void HOperatorSet.LocalMaxSubPix(HObject image, HTuple filter, HTuple sigma, HTuple threshold, out HTuple row, out HTuple column)

void HImage.LocalMaxSubPix(string filter, double sigma, double threshold, out HTuple row, out HTuple column)

def local_max_sub_pix(image: HObject, filter: str, sigma: float, threshold: float) -> Tuple[Sequence[float], Sequence[float]]


local_max_sub_pixlocal_max_sub_pixLocalMaxSubPixLocalMaxSubPixLocalMaxSubPixlocal_max_sub_pix extracts local maxima from the image ImageImageImageImageimageimage with subpixel precision. To do so, in each point the input image is approximated by a quadratic polynomial in x and y and subsequently the polynomial is examined for local maxima. The partial derivatives, which are necessary for setting up the polynomial, are calculated either with various Gaussian derivatives or using the facet model, depending on FilterFilterFilterFilterfilterfilter. In the first case, SigmaSigmaSigmaSigmasigmasigma determines the size of the Gaussian kernels, while in the second case, before being processed the input image is smoothed by a Gaussian whose size is determined by SigmaSigmaSigmaSigmasigmasigma. Therefore, 'facet'"facet""facet""facet""facet""facet" results in a faster extraction at the expense of slightly less accurate results. A point is accepted to be a local maximum if both eigenvalues of the Hessian matrix are smaller than -ThresholdThresholdThresholdThresholdthresholdthreshold. The eigenvalues correspond to the curvature of the gray value surface.


Note that filter operators may return unexpected results if an image with a reduced domain is used as input. Please refer to the chapter Filters.

Execution Information


ImageImageImageImageimageimage (input_object)  singlechannelimage objectHImageHObjectHImageHobject (byte / int1 / int2 / uint2 / int4 / real)

Input image.

FilterFilterFilterFilterfilterfilter (input_control)  string HTuplestrHTupleHtuple (string) (string) (HString) (char*)

Method for the calculation of the partial derivatives.

Default value: 'facet' "facet" "facet" "facet" "facet" "facet"

List of values: 'facet'"facet""facet""facet""facet""facet", 'gauss'"gauss""gauss""gauss""gauss""gauss"

SigmaSigmaSigmaSigmasigmasigma (input_control)  real HTuplefloatHTupleHtuple (real) (double) (double) (double)

Sigma of the Gaussian. If FilterFilterFilterFilterfilterfilter is 'facet', SigmaSigmaSigmaSigmasigmasigma may be 0.0 to avoid the smoothing of the input image.

Suggested values: 0.7, 0.8, 0.9, 1.0, 1.2, 1.5, 2.0, 3.0

Restriction: Sigma >= 0.0

ThresholdThresholdThresholdThresholdthresholdthreshold (input_control)  real HTuplefloatHTupleHtuple (real) (double) (double) (double)

Minimum absolute value of the eigenvalues of the Hessian matrix.

Default value: 5.0

Suggested values: 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0

Restriction: Threshold >= 0.0

RowRowRowRowrowrow (output_control)  point.y-array HTupleSequence[float]HTupleHtuple (real) (double) (double) (double)

Row coordinates of the detected maxima.

ColumnColumnColumnColumncolumncolumn (output_control)  point.x-array HTupleSequence[float]HTupleHtuple (real) (double) (double) (double)

Column coordinates of the detected maxima.


local_max_sub_pixlocal_max_sub_pixLocalMaxSubPixLocalMaxSubPixLocalMaxSubPixlocal_max_sub_pix returns 2 (H_MSG_TRUE) if all parameters are correct and no error occurs during the execution. If the input is empty the behavior can be set via set_system('no_object_result',<Result>)set_system("no_object_result",<Result>)SetSystem("no_object_result",<Result>)SetSystem("no_object_result",<Result>)SetSystem("no_object_result",<Result>)set_system("no_object_result",<Result>). If necessary, an exception is raised.

Possible Successors

gen_cross_contour_xldgen_cross_contour_xldGenCrossContourXldGenCrossContourXldGenCrossContourXldgen_cross_contour_xld, disp_crossdisp_crossDispCrossDispCrossDispCrossdisp_cross


critical_points_sub_pixcritical_points_sub_pixCriticalPointsSubPixCriticalPointsSubPixCriticalPointsSubPixcritical_points_sub_pix, local_min_sub_pixlocal_min_sub_pixLocalMinSubPixLocalMinSubPixLocalMinSubPixlocal_min_sub_pix, saddle_points_sub_pixsaddle_points_sub_pixSaddlePointsSubPixSaddlePointsSubPixSaddlePointsSubPixsaddle_points_sub_pix

See also

local_maxlocal_maxLocalMaxLocalMaxLocalMaxlocal_max, plateausplateausPlateausPlateausPlateausplateaus, plateaus_centerplateaus_centerPlateausCenterPlateausCenterPlateausCenterplateaus_center