HALCON Reference Manual 10.0.2
Table of Contents / Filters / Points ClassesClassesClasses | | | Operators

points_harrisT_points_harrispoints_harrisPointsHarrisPointsHarris (Operator)

Name

points_harrisT_points_harrispoints_harrisPointsHarrisPointsHarris — Detect points of interest using the Harris operator.

Signature

points_harris(Image : : SigmaGrad, SigmaSmooth, Alpha, Threshold : Row, Column)

Herror T_points_harris(const Hobject Image, const Htuple SigmaGrad, const Htuple SigmaSmooth, const Htuple Alpha, const Htuple Threshold, Htuple* Row, Htuple* Column)

Herror points_harris(Hobject Image, const HTuple& SigmaGrad, const HTuple& SigmaSmooth, const HTuple& Alpha, const HTuple& Threshold, HTuple* Row, HTuple* Column)

HTuple HImage::PointsHarris(const HTuple& SigmaGrad, const HTuple& SigmaSmooth, const HTuple& Alpha, const HTuple& Threshold, HTuple* Column) const

void HOperatorSetX.PointsHarris(
[in] IHUntypedObjectX* Image, [in] VARIANT SigmaGrad, [in] VARIANT SigmaSmooth, [in] VARIANT Alpha, [in] VARIANT Threshold, [out] VARIANT* Row, [out] VARIANT* Column)

VARIANT HImageX.PointsHarris(
[in] double SigmaGrad, [in] double SigmaSmooth, [in] double Alpha, [in] VARIANT Threshold, [out] VARIANT* Column)

static void HOperatorSet.PointsHarris(HObject image, HTuple sigmaGrad, HTuple sigmaSmooth, HTuple alpha, HTuple threshold, out HTuple row, out HTuple column)

void HImage.PointsHarris(double sigmaGrad, double sigmaSmooth, double alpha, HTuple threshold, out HTuple row, out HTuple column)

void HImage.PointsHarris(double sigmaGrad, double sigmaSmooth, double alpha, double threshold, out HTuple row, out HTuple column)

Description

points_harrispoints_harrispoints_harrisPointsHarrisPointsHarris extracts points of interest from an image. The Harris operator is based upon the smoothed matrix 

        /   n                n              \
        |  ---              ---             |
        |  \        2       \               |
        |  /    Ix,c        /    Ix,c Iy,c  |
        |  ---              ---             |
        |  c=1              c=1             |
M = G * |                                   |,
        |   n                n              |
        |  ---              ---             |
        |  \                \        2      |
        |  /    Ix,c Iy,c   /    Iy,c       |
        |  ---              ---             |
        \  c=1              c=1             /

where G stands for a Gaussian smoothing of size SigmaSmoothSigmaSmoothSigmaSmoothSigmaSmoothsigmaSmooth and Ix,c and Iy,c are the first derivatives of each image channel, computed with Gaussian derivatives of size SigmaGradSigmaGradSigmaGradSigmaGradsigmaGrad. The resulting points are the positive local extrema of 

                         2
Det(M) - AlphaAlphaAlphaAlphaalpha*(Trace(M)) .

If necessary, they can be restricted to points with a minimum filter response of ThresholdThresholdThresholdThresholdthreshold. The coordinates of the points are calculated with subpixel accuracy.

Attention

points_harrispoints_harrispoints_harrisPointsHarrisPointsHarris uses a special implementation that is optimized using SSE2 instructions if the system parameter 'sse2_enable'"sse2_enable""sse2_enable""sse2_enable""sse2_enable" is set to 'true'"true""true""true""true" (which is default if SSE2 is available on your machine). This implementation is slightly inaccurate compared to the pure C version due to numerical issues (for 'byte' images the difference in RowRowRowRowrow and ColumnColumnColumnColumncolumn is in order of magnitude of 1.0e-5). If you prefer accuracy over performance you can set 'sse2_enable'"sse2_enable""sse2_enable""sse2_enable""sse2_enable" to 'false'"false""false""false""false" (using set_systemset_systemset_systemSetSystemSetSystem) before you call points_harrispoints_harrispoints_harrisPointsHarrisPointsHarris. This way points_harrispoints_harrispoints_harrisPointsHarrisPointsHarris does not use SSE2 accelerations. Don't forget to set 'sse2_enable'"sse2_enable""sse2_enable""sse2_enable""sse2_enable" back to 'true'"true""true""true""true" afterwards.

points_harrispoints_harrispoints_harrisPointsHarrisPointsHarris can be executed on an OpenCL device if both SigmaGradSigmaGradSigmaGradSigmaGradsigmaGrad and SigmaSmoothSigmaSmoothSigmaSmoothSigmaSmoothsigmaSmooth induce a filter size of no more than 129 pixels. This corresponds to a value of less than 20.7 for both parameters. As with the SSE2 version, the results of the OpenCL implementation may diverge slightly from that of pure C version due to numerical issues.

Parallelization

Parameters

ImageImageImageImageimage (input_object)  (multichannel-)image → objectHImageHImageHImageXHobject (byte* / uint2* / real*) *allowed for compute devices

Input image.

SigmaGradSigmaGradSigmaGradSigmaGradsigmaGrad (input_control)  real → HTupleHTupleVARIANTHtuple (real) (double) (double) (double) (double)

Amount of smoothing used for the calculation of the gradient.

Default value: 0.7

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

Typical range of values: 0.7 ≤ SigmaGrad SigmaGrad SigmaGrad SigmaGrad sigmaGrad ≤ 50.0

Recommended increment: 0.1

Restriction: SigmaGrad > 0.0

SigmaSmoothSigmaSmoothSigmaSmoothSigmaSmoothsigmaSmooth (input_control)  real → HTupleHTupleVARIANTHtuple (real) (double) (double) (double) (double)

Amount of smoothing used for the integration of the gradients.

Default value: 2.0

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

Typical range of values: 0.7 ≤ SigmaSmooth SigmaSmooth SigmaSmooth SigmaSmooth sigmaSmooth ≤ 50.0

Recommended increment: 0.1

Restriction: SigmaSmooth > 0.0

AlphaAlphaAlphaAlphaalpha (input_control)  real → HTupleHTupleVARIANTHtuple (real) (double) (double) (double) (double)

Weight of the squared trace of the squared gradient matrix.

Default value: 0.08

Suggested values: 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08

Typical range of values: 0.001 ≤ Alpha Alpha Alpha Alpha alpha ≤ 0.1

Minimum increment: 0.001

Recommended increment: 0.01

Restriction: Alpha > 0.0

ThresholdThresholdThresholdThresholdthreshold (input_control)  number → HTupleHTupleVARIANTHtuple (real / integer) (double / int / long) (double / Hlong) (double / Hlong) (double / Hlong)

Minimum filter response for the points.

Default value: 1000.0

Restriction: Threshold >= 0.0

RowRowRowRowrow (output_control)  point.y-array → HTupleHTupleVARIANTHtuple (real) (double) (double) (double) (double)

Row coordinates of the detected points.

ColumnColumnColumnColumncolumn (output_control)  point.x-array → HTupleHTupleVARIANTHtuple (real) (double) (double) (double) (double)

Column coordinates of the detected points.

Result

points_harrispoints_harrispoints_harrisPointsHarrisPointsHarris 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>)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_xldgen_cross_contour_xldGenCrossContourXldGenCrossContourXld

Alternatives

points_foerstnerpoints_foerstnerpoints_foerstnerPointsFoerstnerPointsFoerstner, points_lepetitpoints_lepetitpoints_lepetitPointsLepetitPointsLepetit, points_harris_binomialpoints_harris_binomialpoints_harris_binomialPointsHarrisBinomialPointsHarrisBinomial

References

C. Harris, M. Stephens: “A combined corner and edge detector”. Proceedings of the 4th Alvey Vision Conference, pp. 147-151, 1988.
V. Gouet, N.Boujemaa: “Object-based queries using color points of interest”. IEEE Workshop on Content-Based Access of Image and Video Libraries, CVPR/CBAIVL 2001, Hawaii, USA, 2001.

Module

Foundation

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HALCON Reference Manual 10.0.2 Copyright © 1996-2011 MVTec Software GmbH