laplacelaplaceLaplaceLaplace (Operator)


laplacelaplaceLaplaceLaplace — Calculate the Laplace operator by using finite differences.


laplace(Image : ImageLaplace : ResultType, MaskSize, FilterMask : )

Herror laplace(const Hobject Image, Hobject* ImageLaplace, const char* ResultType, const Hlong MaskSize, const char* FilterMask)

Herror T_laplace(const Hobject Image, Hobject* ImageLaplace, const Htuple ResultType, const Htuple MaskSize, const Htuple FilterMask)

void Laplace(const HObject& Image, HObject* ImageLaplace, const HTuple& ResultType, const HTuple& MaskSize, const HTuple& FilterMask)

HImage HImage::Laplace(const HString& ResultType, const HTuple& MaskSize, const HString& FilterMask) const

HImage HImage::Laplace(const HString& ResultType, Hlong MaskSize, const HString& FilterMask) const

HImage HImage::Laplace(const char* ResultType, Hlong MaskSize, const char* FilterMask) const

HImage HImage::Laplace(const wchar_t* ResultType, Hlong MaskSize, const wchar_t* FilterMask) const   (Windows only)

static void HOperatorSet.Laplace(HObject image, out HObject imageLaplace, HTuple resultType, HTuple maskSize, HTuple filterMask)

HImage HImage.Laplace(string resultType, HTuple maskSize, string filterMask)

HImage HImage.Laplace(string resultType, int maskSize, string filterMask)


laplacelaplaceLaplaceLaplaceLaplace filters the input images ImageImageImageImageimage using a Laplace operator. Depending on the parameter FilterMaskFilterMaskFilterMaskFilterMaskfilterMask the following approximations of the Laplace operator are used:


1 1 -4 1 1


1 1 1 1 -8 1 1 1 1


10 22 10 22 -128 22 10 22 10

For the three filter masks the following normalizations of the resulting gray values is applied, (i.e., by dividing the result by the given divisor): 'n_4' normalization by 1, 'n_8', normalization by 2 and for 'n_8_isotropic' normalization by 32.

For a Laplace operator with size 3x3, the corresponding filter is applied directly, while for larger filter sizes the input image is first smoothed using a Gaussian filter (see gauss_imagegauss_imageGaussImageGaussImageGaussImage) or a binomial filter (see binomial_filterbinomial_filterBinomialFilterBinomialFilterBinomialFilter) of size MaskSizeMaskSizeMaskSizeMaskSizemaskSize-2. The Gaussian filter is selected for the above values of ResultTypeResultTypeResultTypeResultTyperesultType. Here, MaskSizeMaskSizeMaskSizeMaskSizemaskSize = 5, 7, 9, 11, or 13 must be used. The binomial filter is selected by appending '_binomial'"_binomial""_binomial""_binomial""_binomial" to the above values of ResultTypeResultTypeResultTypeResultTyperesultType. Here, MaskSizeMaskSizeMaskSizeMaskSizemaskSize can be selected between 5 and 39. Furthermore, it is possible to select different amounts of smoothing for the column and row direction by passing two values in MaskSizeMaskSizeMaskSizeMaskSizemaskSize. Here, the first value of MaskSizeMaskSizeMaskSizeMaskSizemaskSize corresponds to the mask width (smoothing in the column direction), while the second value corresponds to the mask height (smoothing in the row direction) of the binomial filter. Therefore, laplace(O:R:'absolute',MaskSize,N:) for MaskSize > 3 is equivalent to gauss_image(O:G:MaskSize-2:) > laplace(G:R:'absolute',3,N:). and laplace(O:R:'absolute_binomial',MaskSize,N:) is equivalent to binomial_filter(O:B:MaskSize-2,MaskSize-2:) > laplace(B:R:'absolute',3,N:).

laplacelaplaceLaplaceLaplaceLaplace either returns the absolute value of the Laplace filtered image (ResultTypeResultTypeResultTypeResultTyperesultType = 'absolute'"absolute""absolute""absolute""absolute") in a byte or uint2 image or the signed result (ResultTypeResultTypeResultTypeResultTyperesultType = 'signed'"signed""signed""signed""signed" or 'signed_clipped'"signed_clipped""signed_clipped""signed_clipped""signed_clipped"). Here, the output image type has the same number of bytes per pixel as the input image (i.e., int1 or int2) for 'signed_clipped'"signed_clipped""signed_clipped""signed_clipped""signed_clipped", while the output image has the next larger number of pixels (i.e., int2 or int4) for 'signed'"signed""signed""signed""signed".


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


ImageImageImageImageimage (input_object)  (multichannel-)image(-array) objectHImageHImageHobject (byte / uint2)

Input image.

ImageLaplaceImageLaplaceImageLaplaceImageLaplaceimageLaplace (output_object)  (multichannel-)image(-array) objectHImageHImageHobject * (byte / uint2 / int2 / int2 / int4)

Laplace-filtered result image.

ResultTypeResultTypeResultTypeResultTyperesultType (input_control)  string HTupleHTupleHtuple (string) (string) (HString) (char*)

Type of the result image, whereas for byte and uint2 the absolute value is used.

Default value: 'absolute' "absolute" "absolute" "absolute" "absolute"

List of values: 'absolute'"absolute""absolute""absolute""absolute", 'absolute_binomial'"absolute_binomial""absolute_binomial""absolute_binomial""absolute_binomial", 'signed'"signed""signed""signed""signed", 'signed_binomial'"signed_binomial""signed_binomial""signed_binomial""signed_binomial", 'signed_clipped'"signed_clipped""signed_clipped""signed_clipped""signed_clipped", 'signed_clipped_binomial'"signed_clipped_binomial""signed_clipped_binomial""signed_clipped_binomial""signed_clipped_binomial"

MaskSizeMaskSizeMaskSizeMaskSizemaskSize (input_control)  integer(-array) HTupleHTupleHtuple (integer) (int / long) (Hlong) (Hlong)

Size of filter mask.

Default value: 3

List of values: 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39

FilterMaskFilterMaskFilterMaskFilterMaskfilterMask (input_control)  string HTupleHTupleHtuple (string) (string) (HString) (char*)

Filter mask used in the Laplace operator

Default value: 'n_4' "n_4" "n_4" "n_4" "n_4"

List of values: 'n_4'"n_4""n_4""n_4""n_4", 'n_8'"n_8""n_8""n_8""n_8", 'n_8_isotropic'"n_8_isotropic""n_8_isotropic""n_8_isotropic""n_8_isotropic"

Example (C)



laplacelaplaceLaplaceLaplaceLaplace returns 2 (H_MSG_TRUE) if all parameters are correct. 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>). If necessary, an exception is raised.

Possible Successors

zero_crossingzero_crossingZeroCrossingZeroCrossingZeroCrossing, dual_thresholddual_thresholdDualThresholdDualThresholdDualThreshold, thresholdthresholdThresholdThresholdThreshold


diff_of_gaussdiff_of_gaussDiffOfGaussDiffOfGaussDiffOfGauss, laplace_of_gausslaplace_of_gaussLaplaceOfGaussLaplaceOfGaussLaplaceOfGauss, derivate_gaussderivate_gaussDerivateGaussDerivateGaussDerivateGauss

See also

highpass_imagehighpass_imageHighpassImageHighpassImageHighpassImage, edges_imageedges_imageEdgesImageEdgesImageEdgesImage