Gwyddion – Free SPM (AFM, SNOM/NSOM, STM, MFM, …) data analysis software

filters

filters — Convolution and other 2D data filters

Functions

void gwy_data_field_normalize ()
void gwy_data_field_renormalize ()
void gwy_data_field_area_renormalize ()
gint gwy_data_field_threshold ()
gint gwy_data_field_area_threshold ()
gint gwy_data_field_clamp ()
gint gwy_data_field_area_clamp ()
void gwy_data_field_area_gather ()
void gwy_data_field_convolve ()
void gwy_data_field_area_convolve ()
void gwy_data_field_area_ext_convolve ()
void gwy_data_field_convolve_1d ()
void gwy_data_field_area_convolve_1d ()
void gwy_data_field_area_ext_row_convolve ()
void gwy_data_field_filter_median ()
void gwy_data_field_area_filter_median ()
void gwy_data_field_filter_mean ()
void gwy_data_field_area_filter_mean ()
void gwy_data_field_filter_conservative ()
void gwy_data_field_area_filter_conservative ()
void gwy_data_field_filter_laplacian ()
void gwy_data_field_area_filter_laplacian ()
void gwy_data_field_filter_laplacian_of_gaussians ()
void gwy_data_field_area_filter_laplacian_of_gaussians ()
void gwy_data_field_filter_sobel ()
void gwy_data_field_area_filter_sobel ()
void gwy_data_field_filter_sobel_total ()
void gwy_data_field_filter_prewitt ()
void gwy_data_field_area_filter_prewitt ()
void gwy_data_field_filter_prewitt_total ()
void gwy_data_field_filter_slope ()
void gwy_data_field_filter_dechecker ()
void gwy_data_field_area_filter_dechecker ()
void gwy_data_field_filter_gaussian ()
void gwy_data_field_area_filter_gaussian ()
void gwy_data_field_filter_minimum ()
void gwy_data_field_area_filter_minimum ()
void gwy_data_field_filter_maximum ()
void gwy_data_field_area_filter_maximum ()
void gwy_data_field_area_filter_min_max ()
void gwy_data_field_area_filter_disc_asf ()
gboolean gwy_data_field_area_filter_kth_rank ()
gboolean gwy_data_field_area_filter_trimmed_mean ()
void gwy_data_field_filter_rms ()
void gwy_data_field_area_filter_rms ()
void gwy_data_field_filter_kuwahara ()
void gwy_data_field_area_filter_kuwahara ()
void gwy_data_field_filter_canny ()
void gwy_data_field_shade ()
void gwy_data_field_filter_harris ()
void gwy_data_field_deconvolve_regularized ()
void gwy_data_field_deconvolve_psf_leastsq ()
gdouble gwy_data_field_find_regularization_sigma_for_psf ()
gdouble gwy_data_field_find_regularization_sigma_leastsq ()

Includes

#include <libprocess/gwyprocess.h>

Description

Filters are point-wise operations, such as thresholding, or generally local operations producing a value based on the data in the vicinity of each point: gradients, step detectors and convolutions. Some simple common point-wise operations, e.g. value inversion, are also found in base GwyDataField methods.

Functions

gwy_data_field_normalize ()

void
gwy_data_field_normalize (GwyDataField *data_field);

Normalizes data in a data field to range 0.0 to 1.0.

It is equivalent to gwy_data_field_renormalize(data_field , 1.0, 0.0);

If data_field is filled with only one value, it is changed to 0.0.

Parameters

data_field

A data field.

 

gwy_data_field_renormalize ()

void
gwy_data_field_renormalize (GwyDataField *data_field,
                            gdouble range,
                            gdouble offset);

Transforms data in a data field with linear function to given range.

When range is positive, the new data range is (offset , offset +range ); when range is negative, the new data range is (offset -range , offset ). In neither case the data are flipped, negative range only means different selection of boundaries.

When range is zero, this method is equivalent to gwy_data_field_fill(data_field , offset ).

Parameters

data_field

A data field.

 

range

New data interval size.

 

offset

New data interval offset.

 

gwy_data_field_area_renormalize ()

void
gwy_data_field_area_renormalize (GwyDataField *data_field,
                                 gint col,
                                 gint row,
                                 gint width,
                                 gint height,
                                 gdouble range,
                                 gdouble offset);

Transforms data in a part of a data field with linear function to given range.

When range is positive, the new data range is (offset , offset +range ); when range is negative, the new data range is (offset -range , offset ). In neither case the data are flipped, negative range only means different selection of boundaries.

When range is zero, this method is equivalent to gwy_data_field_fill(data_field , offset ).

Parameters

data_field

A data field.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

range

New data interval size.

 

offset

New data interval offset.

 

Since: 2.45

gwy_data_field_threshold ()

gint
gwy_data_field_threshold (GwyDataField *data_field,
                          gdouble threshval,
                          gdouble bottom,
                          gdouble top);

Tresholds values of a data field.

Values smaller than threshold are set to value bottom , values higher than threshold or equal to it are set to value top

Parameters

data_field

A data field.

 

threshval

Threshold value.

 

bottom

Lower replacement value.

 

top

Upper replacement value.

 

Returns

The total number of values above threshold.

gwy_data_field_area_threshold ()

gint
gwy_data_field_area_threshold (GwyDataField *data_field,
                               gint col,
                               gint row,
                               gint width,
                               gint height,
                               gdouble threshval,
                               gdouble bottom,
                               gdouble top);

Tresholds values of a rectangular part of a data field.

Values smaller than threshold are set to value bottom , values higher than threshold or equal to it are set to value top

Parameters

data_field

A data field.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

threshval

Threshold value.

 

bottom

Lower replacement value.

 

top

Upper replacement value.

 

Returns

The total number of values above threshold.

gwy_data_field_clamp ()

gint
gwy_data_field_clamp (GwyDataField *data_field,
                      gdouble bottom,
                      gdouble top);

Limits data field values to a range.

Parameters

data_field

A data field.

 

bottom

Lower limit value.

 

top

Upper limit value.

 

Returns

The number of changed values, i.e., values that were outside [bottom , top ].

gwy_data_field_area_clamp ()

gint
gwy_data_field_area_clamp (GwyDataField *data_field,
                           gint col,
                           gint row,
                           gint width,
                           gint height,
                           gdouble bottom,
                           gdouble top);

Limits values in a rectangular part of a data field to a range.

Parameters

data_field

A data field.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

bottom

Lower limit value.

 

top

Upper limit value.

 

Returns

The number of changed values, i.e., values that were outside [bottom , top ].

gwy_data_field_area_gather ()

void
gwy_data_field_area_gather (GwyDataField *data_field,
                            GwyDataField *result,
                            GwyDataField *buffer,
                            gint hsize,
                            gint vsize,
                            gboolean average,
                            gint col,
                            gint row,
                            gint width,
                            gint height);

Sums or averages values in reactangular areas around each sample in a data field.

When the gathered area extends out of calculation area, only samples from their intersection are taken into the local sum (or average).

There are no restrictions on values of hsize and vsize with regard to width and height , but they have to be positive.

The result is calculated by the means of two-dimensional rolling sums. One one hand it means the calculation time depends linearly on (width + hsize )*(height + vsize ) instead of width *hsize *height *vsize . On the other hand it means absolute rounding errors of all output values are given by the largest input values, that is relative precision of results small in absolute value may be poor.

Parameters

data_field

A data field.

 

result

A data field to put the result to, it may be data_field itself.

 

buffer

A data field to use as a scratch area, its size must be at least width *height . May be NULL to allocate a private temporary buffer.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

hsize

Horizontal size of gathered area. The area is centered around each sample if hsize is odd, it extends one pixel more to the right if hsize is even.

 

vsize

Vertical size of gathered area. The area is centered around each sample if vsize is odd, it extends one pixel more down if vsize is even.

 

average

TRUE to divide resulting sums by the number of involved samples to get averages instead of sums.

 

gwy_data_field_convolve ()

void
gwy_data_field_convolve (GwyDataField *data_field,
                         GwyDataField *kernel_field);

Convolves a data field with given kernel.

Parameters

data_field

A data field to convolve. It must be at least as large as 1/3 of kernel_field in each dimension.

 

kernel_field

Kenrel field to convolve data_field with.

 

gwy_data_field_area_convolve ()

void
gwy_data_field_area_convolve (GwyDataField *data_field,
                              GwyDataField *kernel_field,
                              gint col,
                              gint row,
                              gint width,
                              gint height);

Convolves a rectangular part of a data field with given kernel.

Parameters

data_field

A data field to convolve. It must be at least as large as 1/3 of kernel_field in each dimension.

 

kernel_field

Kenrel field to convolve data_field with.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

gwy_data_field_area_ext_convolve ()

void
gwy_data_field_area_ext_convolve (GwyDataField *field,
                                  guint col,
                                  guint row,
                                  guint width,
                                  guint height,
                                  GwyDataField *target,
                                  GwyDataField *kernel,
                                  GwyExteriorType exterior,
                                  gdouble fill_value,
                                  gboolean as_integral);

Convolve a field with a two-dimensional kernel.

Pixel dimensions of target may match either field or just the rectangular area. In the former case the result is written in the same rectangular area; in the latter case the result fills the entire target .

The convolution is performed with the kernel centred on the respective field pixels. For directions in which the kernel has an odd size this holds precisely. For an even-sized kernel this means the kernel centre is placed 0.5 pixel left or up (towards lower indices) from the respective field pixel.

See gwy_data_field_extend() for what constitutes the exterior and how it is handled.

If as_integral is FALSE the function performs a simple discrete convolution sum and the value units of target are set to product of field and kernel units.

If as_integral is TRUE the function approximates a convolution integral. In this case kernel should be a sampled continuous transfer function. The units of value target are set to product of field and kernel value units and field lateral units squared. Furthermore, the discrete sum is multiplied by the pixel size (i.e. dx dy in the integral).

In either case, the lateral units and pixel size of kernel are assumed to be the same as for field (albeit not checked), because the convolution does not make sense otherwise.

Parameters

field

A two-dimensional data field.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

target

A two-dimensional data field where the result will be placed. It may be field for an in-place modification.

 

kernel

Kernel to convolve field with.

 

exterior

Exterior pixels handling.

 

fill_value

The value to use with GWY_EXTERIOR_FIXED_VALUE exterior.

 

as_integral

TRUE for normalisation and units as a convolution integral, FALSE as a sum.

 

Since: 2.49

gwy_data_field_convolve_1d ()

void
gwy_data_field_convolve_1d (GwyDataField *data_field,
                            GwyDataLine *kernel_line,
                            GwyOrientation orientation);

Convolves a data field with given linear kernel.

Parameters

data_field

A data field to convolve. It must be at least as large as 1/3 of kernel_field in the corresponding dimension.

 

kernel_line

Kenrel line to convolve data_field with.

 

orientation

Filter orientation (see gwy_data_field_area_convolve_1d()).

 

Since: 2.4

gwy_data_field_area_convolve_1d ()

void
gwy_data_field_area_convolve_1d (GwyDataField *data_field,
                                 GwyDataLine *kernel_line,
                                 GwyOrientation orientation,
                                 gint col,
                                 gint row,
                                 gint width,
                                 gint height);

Convolves a rectangular part of a data field with given linear kernel.

For large separable kernels it can be more efficient to use a sequence of horizontal and vertical convolutions instead one 2D convolution.

Parameters

data_field

A data field to convolve. It must be at least as large as 1/3 of kernel_field in the corresponding dimension.

 

kernel_line

Kernel line to convolve data_field with.

 

orientation

Filter orientation (GWY_ORIENTATION_HORIZONTAL for row-wise convolution, GWY_ORIENTATION_VERTICAL for column-wise convolution).

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

Since: 2.4

gwy_data_field_area_ext_row_convolve ()

void
gwy_data_field_area_ext_row_convolve (GwyDataField *field,
                                      guint col,
                                      guint row,
                                      guint width,
                                      guint height,
                                      GwyDataField *target,
                                      GwyDataLine *kernel,
                                      GwyExteriorType exterior,
                                      gdouble fill_value,
                                      gboolean as_integral);

Convolve a field row-wise with a one-dimensional kernel.

Pixel dimensions of target may match either field or just the rectangular area. In the former case the result is written in the same rectangular area; in the latter case the result fills the entire target .

The convolution is performed with the kernel centred on the respective field pixels. For an odd-sized kernel this holds precisely. For an even-sized kernel this means the kernel centre is placed 0.5 pixel to the left (towards lower column indices) from the respective field pixel.

See gwy_data_field_extend() for what constitutes the exterior and how it is handled.

If as_integral is FALSE the function performs a simple discrete convolution sum and the value units of target are set to product of field and kernel units.

If as_integral is TRUE the function approximates a convolution integral. In this case kernel should be a sampled continuous transfer function. The units of value target are set to product of field and kernel value units and field lateral units. Furthermore, the discrete sum is multiplied by the pixel size (i.e. dx in the integral).

In either case, the lateral units and pixel size of kernel are assumed to be the same as for a field 's row (albeit not checked), because the convolution does not make sense otherwise.

Parameters

field

A two-dimensional data field.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

target

A two-dimensional data field where the result will be placed. It may be field for an in-place modification.

 

kernel

Kernel to convolve field with.

 

exterior

Exterior pixels handling.

 

fill_value

The value to use with GWY_EXTERIOR_FIXED_VALUE exterior.

 

as_integral

TRUE for normalisation and units as a convolution integral, FALSE as a sum.

 

Since: 2.49

gwy_data_field_filter_median ()

void
gwy_data_field_filter_median (GwyDataField *data_field,
                              gint size);

Filters a data field with median filter.

This method uses a simple square kernel. Use the general function gwy_data_field_area_filter_kth_rank() to perform filtering with different, for instance circular, kernel.

Parameters

data_field

A data field to apply the filter to.

 

size

Size of area to take median of.

 

gwy_data_field_area_filter_median ()

void
gwy_data_field_area_filter_median (GwyDataField *data_field,
                                   gint size,
                                   gint col,
                                   gint row,
                                   gint width,
                                   gint height);

Filters a rectangular part of a data field with median filter.

This method uses a simple square kernel. Use the general function gwy_data_field_area_filter_kth_rank() to perform filtering with different, for instance circular, kernel.

Parameters

data_field

A data field to apply the filter to.

 

size

Size of area to take median of.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

gwy_data_field_filter_mean ()

void
gwy_data_field_filter_mean (GwyDataField *data_field,
                            gint size);

Filters a data field with mean filter of size size .

This method is a simple gwy_data_field_area_gather() wrapper, so the kernel is square. Use convolution gwy_data_field_area_ext_convolve() to perform a mean filter with different, for instance circular, kernel.

Parameters

data_field

A data field to apply the filter to.

 

size

Averaged area size.

 

gwy_data_field_area_filter_mean ()

void
gwy_data_field_area_filter_mean (GwyDataField *data_field,
                                 gint size,
                                 gint col,
                                 gint row,
                                 gint width,
                                 gint height);

Filters a rectangular part of a data field with mean filter of size size .

This method is a simple gwy_data_field_area_gather() wrapper, so the kernel is square. Use convolution gwy_data_field_area_ext_convolve() to perform a mean filter with different, for instance circular, kernel.

Parameters

data_field

A data field to apply the filter to.

 

size

Averaged area size.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

gwy_data_field_filter_conservative ()

void
gwy_data_field_filter_conservative (GwyDataField *data_field,
                                    gint size);

Filters a data field with conservative denoise filter.

Parameters

data_field

A data field to apply the filter to.

 

size

Filtered area size.

 

gwy_data_field_area_filter_conservative ()

void
gwy_data_field_area_filter_conservative
                               (GwyDataField *data_field,
                                gint size,
                                gint col,
                                gint row,
                                gint width,
                                gint height);

Filters a rectangular part of a data field with conservative denoise filter.

Parameters

data_field

A data field to apply the filter to.

 

size

Filtered area size.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

gwy_data_field_filter_laplacian ()

void
gwy_data_field_filter_laplacian (GwyDataField *data_field);

Filters a data field with Laplacian filter.

Parameters

data_field

A data field to apply the filter to.

 

gwy_data_field_area_filter_laplacian ()

void
gwy_data_field_area_filter_laplacian (GwyDataField *data_field,
                                      gint col,
                                      gint row,
                                      gint width,
                                      gint height);

Filters a rectangular part of a data field with Laplacian filter.

Parameters

data_field

A data field to apply the filter to.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

gwy_data_field_filter_laplacian_of_gaussians ()

void
gwy_data_field_filter_laplacian_of_gaussians
                               (GwyDataField *data_field);

Filters a data field with Laplacian of Gaussians filter.

Parameters

data_field

A data field to apply the filter to.

 

Since: 2.23

gwy_data_field_area_filter_laplacian_of_gaussians ()

void
gwy_data_field_area_filter_laplacian_of_gaussians
                               (GwyDataField *data_field,
                                gint col,
                                gint row,
                                gint width,
                                gint height);

Filters a rectangular part of a data field with Laplacian of Gaussians filter.

Parameters

data_field

A data field to apply the filter to.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

Since: 2.23

gwy_data_field_filter_sobel ()

void
gwy_data_field_filter_sobel (GwyDataField *data_field,
                             GwyOrientation orientation);

Filters a data field with a directional Sobel filter.

Parameters

data_field

A data field to apply the filter to.

 

orientation

Filter orientation.

 

gwy_data_field_area_filter_sobel ()

void
gwy_data_field_area_filter_sobel (GwyDataField *data_field,
                                  GwyOrientation orientation,
                                  gint col,
                                  gint row,
                                  gint width,
                                  gint height);

Filters a rectangular part of a data field with a directional Sobel filter.

Parameters

data_field

A data field to apply the filter to.

 

orientation

Filter orientation.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

gwy_data_field_filter_sobel_total ()

void
gwy_data_field_filter_sobel_total (GwyDataField *data_field);

Filters a data field with total Sobel filter.

Parameters

data_field

A data field to apply the filter to.

 

Since: 2.31

gwy_data_field_filter_prewitt ()

void
gwy_data_field_filter_prewitt (GwyDataField *data_field,
                               GwyOrientation orientation);

Filters a data field with Prewitt filter.

Parameters

data_field

A data field to apply the filter to.

 

orientation

Filter orientation.

 

gwy_data_field_area_filter_prewitt ()

void
gwy_data_field_area_filter_prewitt (GwyDataField *data_field,
                                    GwyOrientation orientation,
                                    gint col,
                                    gint row,
                                    gint width,
                                    gint height);

Filters a rectangular part of a data field with a directional Prewitt filter.

Parameters

data_field

A data field to apply the filter to.

 

orientation

Filter orientation.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

gwy_data_field_filter_prewitt_total ()

void
gwy_data_field_filter_prewitt_total (GwyDataField *data_field);

Filters a data field with total Prewitt filter.

Parameters

data_field

A data field to apply the filter to.

 

Since: 2.31

gwy_data_field_filter_slope ()

void
gwy_data_field_filter_slope (GwyDataField *data_field,
                             GwyDataField *xder,
                             GwyDataField *yder);

Calculates x and y derivaties for an entire field.

The derivatives are calculated as the simple symmetrical differences (in physical units, not pixel-wise), except at the edges where the differences are one-sided.

Parameters

data_field

A data field to apply the filter to.

 

xder

Data field where the x-derivarive is to be stored, or NULL if you are only interested in the y-derivarive.

 

yder

Data field where the y-derivarive is to be stored, or NULL if you are only interested in the x-derivarive.

 

Since: 2.37

gwy_data_field_filter_dechecker ()

void
gwy_data_field_filter_dechecker (GwyDataField *data_field);

Filters a data field with 5x5 checker pattern removal filter.

Parameters

data_field

A data field to apply the filter to.

 

Since: 2.1

gwy_data_field_area_filter_dechecker ()

void
gwy_data_field_area_filter_dechecker (GwyDataField *data_field,
                                      gint col,
                                      gint row,
                                      gint width,
                                      gint height);

Filters a rectangular part of a data field with 5x5 checker pattern removal filter.

Parameters

data_field

A data field to apply the filter to.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

Since: 2.1

gwy_data_field_filter_gaussian ()

void
gwy_data_field_filter_gaussian (GwyDataField *data_field,
                                gdouble sigma);

Filters a data field with a Gaussian filter.

Parameters

data_field

A data field to apply the filter to.

 

sigma

The sigma parameter of the Gaussian.

 

Since: 2.4

gwy_data_field_area_filter_gaussian ()

void
gwy_data_field_area_filter_gaussian (GwyDataField *data_field,
                                     gdouble sigma,
                                     gint col,
                                     gint row,
                                     gint width,
                                     gint height);

Filters a rectangular part of a data field with a Gaussian filter.

The Gausian is normalized, i.e. it is sum-preserving.

Parameters

data_field

A data field to apply the filter to.

 

sigma

The sigma parameter of the Gaussian.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

Since: 2.4

gwy_data_field_filter_minimum ()

void
gwy_data_field_filter_minimum (GwyDataField *data_field,
                               gint size);

Filters a data field with minimum filter.

This method uses a simple square kernel. Use the general function gwy_data_field_area_filter_min_max() to perform filtering with different, for instance circular, kernel.

Parameters

data_field

A data field to apply minimum filter to.

 

size

Neighbourhood size for minimum search.

 

gwy_data_field_area_filter_minimum ()

void
gwy_data_field_area_filter_minimum (GwyDataField *data_field,
                                    gint size,
                                    gint col,
                                    gint row,
                                    gint width,
                                    gint height);

Filters a rectangular part of a data field with minimum filter.

This operation is often called erosion filter.

This method uses a simple square kernel. Use the general function gwy_data_field_area_filter_min_max() to perform filtering with different, for instance circular, kernel.

Parameters

data_field

A data field to apply minimum filter to.

 

size

Neighbourhood size for minimum search.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

gwy_data_field_filter_maximum ()

void
gwy_data_field_filter_maximum (GwyDataField *data_field,
                               gint size);

Filters a data field with maximum filter.

This method uses a simple square kernel. Use the general function gwy_data_field_area_filter_min_max() to perform filtering with different, for instance circular, kernel.

Parameters

data_field

A data field to apply maximum filter to.

 

size

Neighbourhood size for maximum search.

 

gwy_data_field_area_filter_maximum ()

void
gwy_data_field_area_filter_maximum (GwyDataField *data_field,
                                    gint size,
                                    gint col,
                                    gint row,
                                    gint width,
                                    gint height);

Filters a rectangular part of a data field with maximum filter.

This operation is often called dilation filter.

This method uses a simple square kernel. Use the general function gwy_data_field_area_filter_min_max() to perform filtering with different, for instance circular, kernel.

Parameters

data_field

A data field to apply maximum filter to.

 

size

Neighbourhood size for maximum search.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

gwy_data_field_area_filter_min_max ()

void
gwy_data_field_area_filter_min_max (GwyDataField *data_field,
                                    GwyDataField *kernel,
                                    GwyMinMaxFilterType filtertype,
                                    gint col,
                                    gint row,
                                    gint width,
                                    gint height);

Applies a morphological operation with a flat structuring element to a part of a data field.

Morphological operations with flat structuring elements can be expressed using minimum (erosion) and maximum (dilation) filters that are the basic operations this function can perform.

The kernel field is a mask that defines the shape of the flat structuring element. It is reflected for all maximum operations (dilation). For symmetrical kernels this does not matter. You can use gwy_data_field_elliptic_area_fill() to create a true circular (or elliptical) kernel.

The kernel is implicitly centered, i.e. it will be applied symmetrically to avoid unexpected data movement. Even-sized kernels (generally not recommended) will extend farther towards the top left image corner for minimum (erosion) and towards the bottom right corner for maximum (dilation) operations due to the reflection. If you need off-center structuring elements you can add empty rows or columns to one side of the kernel to counteract the symmetrisation.

The operation is linear-time in kernel size for any convex kernel. Note gwy_data_field_area_filter_minimum() and gwy_data_field_area_filter_maximum(), which are limited to square structuring elements, are much faster for large sizes of the squares.

The exterior is always handled as GWY_EXTERIOR_BORDER_EXTEND.

Parameters

data_field

A data field to apply the filter to.

 

kernel

Data field defining the flat structuring element.

 

filtertype

The type of filter to apply.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

Since: 2.43

gwy_data_field_area_filter_disc_asf ()

void
gwy_data_field_area_filter_disc_asf (GwyDataField *data_field,
                                     gint radius,
                                     gboolean closing,
                                     gint col,
                                     gint row,
                                     gint width,
                                     gint height);

Applies an alternating sequential morphological filter with a flat disc structuring element to a part of a data field.

Alternating sequential filter is a filter consisting of repeated opening and closing (or closing and opening) with progressively larger structuring elements. This function performs such filtering for sequence of structuring elements consisting of true Euclidean discs with increasing radii. The largest disc in the sequence fits into a (2size  + 1) × (2size  + 1) square.

Parameters

data_field

A data field to apply the filter to.

 

radius

Maximum radius of the circular structuring element, in pixels. For radius 0 and smaller the filter is no-op.

 

closing

TRUE requests an opening-closing filter (i.e. ending with closing), FALSE requests a closing-opening filter (i.e. ending with opening).

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

Since: 2.43

gwy_data_field_area_filter_kth_rank ()

gboolean
gwy_data_field_area_filter_kth_rank (GwyDataField *data_field,
                                     GwyDataField *kernel,
                                     gint col,
                                     gint row,
                                     gint width,
                                     gint height,
                                     gint k,
                                     GwySetFractionFunc set_fraction);

Applies a k -th rank filter to a part of a data field.

Pass half the number of non-zero values in kernel as k for a median filter.

The kernel field is a mask that defines the shape of the kernel. You can use gwy_data_field_elliptic_area_fill() to create a true circular (or elliptical) kernel. The kernel must be non-empty.

The kernel is implicitly centered, i.e. it will be applied symmetrically to avoid unexpected data movement. Even-sized kernels (generally not recommended) will extend farther towards the top left image corner for minimum (erosion) and towards the bottom right corner for maximum (dilation) operations due to the reflection. If you need off-center structuring elements you can add empty rows or columns to one side of the kernel to counteract the symmetrisation.

The exterior is always handled as GWY_EXTERIOR_BORDER_EXTEND.

If the operation is aborted the contents of data_field is untouched.

Parameters

data_field

A data field to apply the filter to.

 

kernel

Data field defining the kernel shape.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

k

Rank of the value to store as the output (from lowest to highest).

 

set_fraction

Function that sets fraction to output (or NULL).

 

Returns

TRUE if the operation was not aborted via set_fraction returning FALSE; FALSE if it was aborted.

Since: 2.51

gwy_data_field_area_filter_trimmed_mean ()

gboolean
gwy_data_field_area_filter_trimmed_mean
                               (GwyDataField *data_field,
                                GwyDataField *kernel,
                                gint col,
                                gint row,
                                gint width,
                                gint height,
                                gint nlowest,
                                gint nhighest,
                                GwySetFractionFunc set_fraction);

Applies a trimmed mean filter to a part of a data field.

At least one value must remain after the trimming, i.e. nlowest + nhighest must be smaller than the number of non-zero values in kernel . Usually one passes the same number as both nlowest and nhighest , but it is not a requirement.

The kernel field is a mask that defines the shape of the kernel. You can use gwy_data_field_elliptic_area_fill() to create a true circular (or elliptical) kernel. The kernel must be non-empty.

The kernel is implicitly centered, i.e. it will be applied symmetrically to avoid unexpected data movement. Even-sized kernels (generally not recommended) will extend farther towards the top left image corner for minimum (erosion) and towards the bottom right corner for maximum (dilation) operations due to the reflection. If you need off-center structuring elements you can add empty rows or columns to one side of the kernel to counteract the symmetrisation.

The exterior is always handled as GWY_EXTERIOR_BORDER_EXTEND.

If the operation is aborted the contents of data_field is untouched.

Parameters

data_field

A data field to apply the filter to.

 

kernel

Data field defining the kernel shape.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

nlowest

The number of lowest values to discard.

 

nhighest

The number of highest values to discard.

 

set_fraction

Function that sets fraction to output (or NULL).

 

Returns

TRUE if the operation was not aborted via set_fraction returning FALSE; FALSE if it was aborted.

Since: 2.53

gwy_data_field_filter_rms ()

void
gwy_data_field_filter_rms (GwyDataField *data_field,
                           gint size);

Filters a data field with RMS filter.

Parameters

data_field

A data field to apply RMS filter to.

 

size

Area size.

 

gwy_data_field_area_filter_rms ()

void
gwy_data_field_area_filter_rms (GwyDataField *data_field,
                                gint size,
                                gint col,
                                gint row,
                                gint width,
                                gint height);

Filters a rectangular part of a data field with RMS filter of size size .

RMS filter computes root mean square in given area.

Parameters

data_field

A data field to apply RMS filter to.

 

size

Area size.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

gwy_data_field_filter_kuwahara ()

void
gwy_data_field_filter_kuwahara (GwyDataField *data_field);

Filters a data field with Kuwahara filter.

Parameters

data_field

A data field to apply Kuwahara filter to.

 

gwy_data_field_area_filter_kuwahara ()

void
gwy_data_field_area_filter_kuwahara (GwyDataField *data_field,
                                     gint col,
                                     gint row,
                                     gint width,
                                     gint height);

Filters a rectangular part of a data field with a Kuwahara (edge-preserving smoothing) filter.

Parameters

data_field

A data filed to apply Kuwahara filter to.

 

col

Upper-left column coordinate.

 

row

Upper-left row coordinate.

 

width

Area width (number of columns).

 

height

Area height (number of rows).

 

gwy_data_field_filter_canny ()

void
gwy_data_field_filter_canny (GwyDataField *data_field,
                             gdouble threshold);

Filters a rectangular part of a data field with canny edge detector filter.

Parameters

data_field

A data field to apply the filter to.

 

threshold

Slope detection threshold (range 0..1).

 

gwy_data_field_shade ()

void
gwy_data_field_shade (GwyDataField *data_field,
                      GwyDataField *target_field,
                      gdouble theta,
                      gdouble phi);

Shades a data field.

Parameters

data_field

A data field.

 

target_field

A data field to put the shade to. It will be resized to match data_field .

 

theta

Shading angle (in radians, from north pole).

 

phi

Shade orientation in xy plane (in radians, counterclockwise).

 

gwy_data_field_filter_harris ()

void
gwy_data_field_filter_harris (GwyDataField *x_gradient,
                              GwyDataField *y_gradient,
                              GwyDataField *result,
                              gint neighbourhood,
                              gdouble alpha);

Applies Harris corner detection filter to a pair of gradient data fields.

All passed data field must have the same size.

Parameters

x_gradient

Data field with pre-calculated horizontal derivative.

 

y_gradient

Data field with pre-calculated vertical derivative.

 

result

Data field for the result.

 

neighbourhood

Neighbourhood size.

 

alpha

Sensitivity paramter (the squared trace is multiplied by it).

 

gwy_data_field_deconvolve_regularized ()

void
gwy_data_field_deconvolve_regularized (GwyDataField *dfield,
                                       GwyDataField *operand,
                                       GwyDataField *out,
                                       gdouble sigma);

Performs deconvolution of a data field using a simple regularization.

The operation can be used to deblur an image or conversely recover the point spread function from ideal response image.

Convolving the result with the operand using gwy_data_field_area_ext_convolve() with as_integral =TRUE will recover (approximately) the image. This means the deconvolution assumes continous convolution, not discrete sums. Note that for the latter case this means the point spread function will be centered in out .

For recovery of transfer function, dfield and operand should be windowed beforehand if they are not periodic.

Parameters

dfield

A data field.

 

operand

One of the factors entering the convolution resulting in dfield . It must have the same dimensions as dfield and it is assumed it has also the same physical size.

 

out

Data field where to put the result into. It will be resized to match dfield . It can also be dfield itself.

 

sigma

Regularization parameter.

 

Since: 2.51

gwy_data_field_deconvolve_psf_leastsq ()

void
gwy_data_field_deconvolve_psf_leastsq (GwyDataField *dfield,
                                       GwyDataField *operand,
                                       GwyDataField *out,
                                       gdouble sigma,
                                       gint border);

Performs reconstruction of transfer function from convolved and ideal sharp images.

The transfer function is reconstructed by solving the corresponding least squares problem. This method is suitable when the dimensions of out are much smaller than the images.

Since the method accumulates errors close to edges, they can be removed within the procedure by reconstructing a slightly larger transfer function and then cutting the result. The extension is given by border , typical suitable values are 2 or 3.

Convolving the result with the operand using gwy_data_field_area_ext_convolve() with as_integral =TRUE will recover (approximately) the image. This means the deconvolution assumes continous convolution, not discrete sums. Note that for the latter case this means the point spread function will be centered in out .

Fields dfield and operand should be windowed beforehand if they are not periodic.

Parameters

dfield

A data field.

 

operand

Ideal sharp measurement (before convolution). It must have the same dimensions as dfield and it is assumed it has also the same physical size.

 

out

Output field for the transfer function. Its dimensions are preserved and determine the transfer function support. It must be smaller than half of dfield .

 

sigma

Regularization parameter.

 

border

Number of pixel to extend and cut off the transfer function.

 

Since: 2.52

gwy_data_field_find_regularization_sigma_for_psf ()

gdouble
gwy_data_field_find_regularization_sigma_for_psf
                               (GwyDataField *dfield,
                                GwyDataField *ideal);

Finds regularization parameter for point spread function calculation using regularized deconvolution.

The estimated value should be suitable for reconstruction of the point spread function using gwy_data_field_deconvolve_regularized(). The estimate is only suitable for PSF, it does not work for image sharpening using a known PSF.

Parameters

dfield

A data field with convolved noisy data.

 

ideal

A data field with ideal sharp data.

 

Returns

Estimated regularization parameter.

Since: 2.51

gwy_data_field_find_regularization_sigma_leastsq ()

gdouble
gwy_data_field_find_regularization_sigma_leastsq
                               (GwyDataField *dfield,
                                GwyDataField *ideal,
                                gint width,
                                gint height,
                                gint border);

Finds regularization parameter for point spread function calculation using least squares method.

The estimated value should be suitable for reconstruction of the point spread function using gwy_data_field_deconvolve_psf_leastsq().

Parameters

dfield

A data field with convolved noisy data.

 

ideal

A data field with ideal sharp data.

 

width

Horizontal size of transfer function support.

 

height

Vertical size of transfer function support.

 

border

Number of pixel to extend and cut off the transfer function.

 

Returns

Estimated regularization parameter.

Since: 2.52

Types and Values

© David Nečas and Petr Klapetek

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