local_max_sub_pix — Subpixel precise detection of local maxima in an image.
local_max_sub_pix extracts local maxima from the image
Image 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 Filter.
In the first case, Sigma 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 Sigma.
Therefore, '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
-Threshold. 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.
Image (input_object) singlechannelimage → object (byte / int1 / int2 / uint2 / int4 / real)
Input image.
Filter (input_control) string → (string)
Method for the calculation of the partial derivatives.
Default value: 'facet'
List of values: 'facet', 'gauss'
Sigma (input_control) real → (real)
Sigma of the Gaussian.
If Filter is 'facet', Sigma 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
Threshold (input_control) real → (real)
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
Row (output_control) point.y-array → (real)
Row coordinates of the detected maxima.
Column (output_control) point.x-array → (real)
Column coordinates of the detected maxima.
local_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>). If
necessary, an exception is raised.
gen_cross_contour_xld,
disp_cross
critical_points_sub_pix,
local_min_sub_pix,
saddle_points_sub_pix
local_max,
plateaus,
plateaus_center
Foundation