libvips

vips_morph ()

int
vips_morph (VipsImage *in,
            VipsImage **out,
            VipsImage *mask,
            VipsOperationMorphology morph,
            ...);

Performs a morphological operation on in using mask as a structuring element.

The image should have 0 (black) for no object and 255 (non-zero) for an object. Note that this is the reverse of the usual convention for these operations, but more convenient when combined with the boolean operators. The output image is the same size as the input image: edge pxels are made by expanding the input image as necessary.

Mask coefficients can be either 0 (for object) or 255 (for background) or 128 (for do not care). The origin of the mask is at location (m.xsize / 2, m.ysize / 2), integer division. All algorithms have been based on the book "Fundamentals of Digital Image Processing" by A. Jain, pp 384-388, Prentice-Hall, 1989.

For VIPS_OPERATION_MORPHOLOGY_ERODE, the whole mask must match for the output pixel to be set, that is, the result is the logical AND of the selected input pixels.

For VIPS_OPERATION_MORPHOLOGY_DILATE, the output pixel is set if any part of the mask matches, that is, the result is the logical OR of the selected input pixels.

See the boolean operations vips_andimage(), vips_orimage() and vips_eorimage() for analogues of the usual set difference and set union operations.

Operations are performed using the processor's vector unit, if possible. Disable this with --vips-novector or VIPS_NOVECTOR or vips_vector_set_enabled()

[method]

vips_rank ()

int
vips_rank (VipsImage *in,
           VipsImage **out,
           int width,
           int height,
           int index,
           ...);

vips_rank() does rank filtering on an image. A window of size width by height is passed over the image. At each position, the pixels inside the window are sorted into ascending order and the pixel at position index is output. index numbers from 0.

It works for any non-complex image type, with any number of bands. The input is expanded by copying edge pixels before performing the operation so that the output image has the same size as the input. Edge pixels in the output image are therefore only approximate.

For a median filter with mask size m (3 for 3x3, 5 for 5x5, etc.) use

vips_rank(in, out, m, m, m * m / 2);

The special cases n == 0 and n == m * m - 1 are useful dilate and expand operators.

See also: vips_conv(), vips_median(), vips_spcor().

[method]

vips_median ()

int
vips_median (VipsImage *in,
             VipsImage **out,
             int size,
             ...);

A convenience function equivalent to:

vips_rank(in, out, size, size, (size * size) / 2);

See also: vips_rank().

[method]

vips_countlines ()

int
vips_countlines (VipsImage *in,
                 double *nolines,
                 VipsDirection direction,
                 ...);

Function which calculates the number of transitions between black and white for the horizontal or the vertical direction of an image. black<128 , white>=128 The function calculates the number of transitions for all Xsize or Ysize and returns the mean of the result Input should be one band, 8-bit.

See also: vips_morph(), vips_conv().

[method]

vips_labelregions ()

int
vips_labelregions (VipsImage *in,
                   VipsImage **mask,
                   ...);

Optional arguments:

Repeatedly scans in for regions of 4-connected pixels with the same pixel value. Every time a region is discovered, those pixels are marked in mask with a unique serial number. Once all pixels have been labelled, the operation returns, setting segments to the number of discrete regions which were detected.

mask is always a 1-band VIPS_FORMAT_INT image of the same dimensions as in .

This operation is useful for, for example, blob counting. You can use the morphological operators to detect and isolate a series of objects, then use vips_labelregions() to number them all.

Use vips_hist_find_indexed() to (for example) find blob coordinates.

See also: vips_hist_find_indexed().

[method]

vips_fill_nearest ()

int
vips_fill_nearest (VipsImage *in,
                   VipsImage **out,
                   ...);

Optional arguments:

Fill outwards from every non-zero pixel in in , setting pixels in distance and value .

At the position of zero pixels in in , distance contains the distance to the nearest non-zero pixel in in , and value contains the value of that pixel.

distance is a one-band float image. value has the same number of bands and format as in .

See also: vips_hist_find_indexed().

[method]

enum VipsOperationMorphology

More like hit-miss, really.

See also: vips_morph().