laplace

laplace ( Image : ImageLaplace : FilterType, Size, NeighbourhoodType : )

Calculate the Laplace operator by using finite differences.

laplace filters the input images Image using a Laplace operator. Depending on the parameter NeighbourhoodType the following simple 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_isotrop':      
                  10      22     10
                  22     -128    22
                  10      22     10

The filter 'n_8' corresponds to the filter mask used in highpass_image(O:R:3,3:). For a Laplace operator with size 3x3, the corresponding filter is applied directly, while for larger filter sizes (Size = 5,7,9 and 11) the input image is first smoothed using a Gaussian filter of the selected size. Therefore,

     laplace(O:R:int4,S,N:)

for Size > 3 is equivalent to

     gauss_image(O:G:S:) >
     laplace(G:R:int4,3,N:).

laplace either returns the absolute value of the Laplace filtered image (FilterType 'abs') in a byte/uint2-image or the signed result (FilterType 'int4') in an int4-image.

Parameters

`Image` (input_object)	(multichannel-)image(-array) `->` object : byte / uint2
Input image.

`ImageLaplace` (output_object)	(multichannel-)image(-array) `->` object : byte / uint2 / int4
Laplace-filtered result images.

`FilterType` (input_control)	string `->` string
Calculate the absolute value of the filter to a byte/uint2-image or the signed result to an int4-image.
Default value: 'int4'
List of values: 'abs', 'int4'

`Size` (input_control)	integer `->` integer
Size of filter mask.
Default value: 3
List of values: 3, 5, 7, 9, 11

`NeighbourhoodType` (input_control)	string `->` string
Neighborhood used in the Laplace operator
Default value: 'n_8_isotrop'
List of values: 'n_4', 'n_8', 'n_8_isotrop'

Example (Syntax: C)

read_image(&Image,"mreut");
laplace(Image,&Laplace,"int4",3,"n_8_isotrop");
zero_crossing(Laplace,&ZeroCrossings);

Result

laplace returns 2 (H_MSG_TRUE) if all parameters are correct. If the input is empty the behaviour can be set via set_system('no_object_result',<Result>). If necessary, an exception handling is raised.

Parallelization Information

laplace is reentrant and automatically parallelized (on tuple level, channel level, domain level).

Possible Successors

zero_crossing, dual_threshold

Alternatives

diff_of_gauss, laplace_of_gauss

See also

highpass_image, edges_image

Module

Foundation