laplacelaplaceLaplaceLaplace (Operator)

Name

laplacelaplaceLaplaceLaplace — Calculate the Laplace operator by using finite differences.

Signature

Description

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

'n_4'

                           1
                  1       -4      1
                           1

'n_8'

                  1       1       1
                  1       -8      1
                  1       1       1

'n_8_isotropic'

                  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".

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.

Execution Information

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

Parameters

Example (C)

read_image(&Image,"mreut");
laplace(Image,&Laplace,"signed",3,"n_8_isotropic");
zero_crossing(Laplace,&ZeroCrossings);

Result

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

Alternatives

diff_of_gaussdiff_of_gaussDiffOfGaussDiffOfGaussDiffOfGauss, laplace_of_gausslaplace_of_gaussLaplaceOfGaussLaplaceOfGaussLaplaceOfGauss, derivate_gaussderivate_gaussDerivateGaussDerivateGaussDerivateGauss

See also

highpass_imagehighpass_imageHighpassImageHighpassImageHighpassImage, edges_imageedges_imageEdgesImageEdgesImageEdgesImage

Module

Foundation