critical_points_sub_pixT_critical_points_sub_pixCriticalPointsSubPixcritical_points_sub_pixCriticalPointsSubPixCriticalPointsSubPix (Operator)

Name

critical_points_sub_pixT_critical_points_sub_pixCriticalPointsSubPixcritical_points_sub_pixCriticalPointsSubPixCriticalPointsSubPix — Subpixel precise detection of critical points in an image.

Signature

Description

critical_points_sub_pixcritical_points_sub_pixCriticalPointsSubPixcritical_points_sub_pixCriticalPointsSubPixCriticalPointsSubPix extracts critical points, i.e., local maxima, local minima, and saddle points, 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 extremal values and saddle points. 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 critical point if the absolute values of both eigenvalues of the Hessian matrix are greater than ThresholdThresholdThresholdThresholdThresholdthreshold. The eigenvalues correspond to the curvature of the gray value surface. If both eigenvalues are negative, the point is a local maximum, if both are positive, a local minimum, and if they have different signs, a saddle point.

Attention

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.

Parallelization

• Multithreading type: reentrant (runs in parallel with non-exclusive operators).
• Multithreading scope: global (may be called from any thread).
• Automatically parallelized on internal data level.

Parameters

Result

critical_points_sub_pixcritical_points_sub_pixCriticalPointsSubPixcritical_points_sub_pixCriticalPointsSubPixCriticalPointsSubPix 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>)set_system("no_object_result",<Result>)SetSystem("no_object_result",<Result>)SetSystem("no_object_result",<Result>). If necessary, an exception is raised.

Possible Successors

gen_cross_contour_xldgen_cross_contour_xldGenCrossContourXldgen_cross_contour_xldGenCrossContourXldGenCrossContourXld, disp_crossdisp_crossDispCrossdisp_crossDispCrossDispCross

Alternatives

local_min_sub_pixlocal_min_sub_pixLocalMinSubPixlocal_min_sub_pixLocalMinSubPixLocalMinSubPix, local_max_sub_pixlocal_max_sub_pixLocalMaxSubPixlocal_max_sub_pixLocalMaxSubPixLocalMaxSubPix, saddle_points_sub_pixsaddle_points_sub_pixSaddlePointsSubPixsaddle_points_sub_pixSaddlePointsSubPixSaddlePointsSubPix

See also

local_minlocal_minLocalMinlocal_minLocalMinLocalMin, local_maxlocal_maxLocalMaxlocal_maxLocalMaxLocalMax, plateausplateausPlateausplateausPlateausPlateaus, plateaus_centerplateaus_centerPlateausCenterplateaus_centerPlateausCenterPlateausCenter, lowlandslowlandsLowlandslowlandsLowlandsLowlands, lowlands_centerlowlands_centerLowlandsCenterlowlands_centerLowlandsCenterLowlandsCenter

Module

Foundation