Other Alias

im_rank_image, im_maxvalue, im_lindetect, im_gradient## SYNOPSIS

#include <vips/vips.h>
int im_rank_image(in, out, n, index)

IMAGE **in;

IMAGE *out;

int n;

int index;

int im_maxvalue(in, out, n)

IMAGE **in;

IMAGE *out;

int n;

int im_compass(in, out, mask)

IMAGE *in, *out;

INTMASK *mask;

int im_lindetect(in, out, mask)

IMAGE *in, *out;

INTMASK *mask;

int im_gradient(in, out, mask)

IMAGE *in, *out;

INTMASK *mask;

## DESCRIPTION

**im_rank_image()**sorts the input images pixel-wise, then outputs an image in which each pixel is selected from the sorted list by the

**index**parameter. For example, if

**index**is zero, then each output pixel will be the minimum of all the corresponding input pixels. It works for any uncoded, non-complex image type. All input images must match in size, format, and number of bands.

These functions convolve the image pointed by the image descriptor in with the mask pointed by mask and put the result in the image pointed by out.

The mask structure INTMASK is returned by the function im_read_imask(3), for integer mask only. Input should be unsigned char; processing is carried out using look-up tables. The output is integer. coefficients. The size of the output image and the number of channels are the same as the corresponding of the input.

The output image is the same size as the input. The edge pixels are calculated
by expanding the input image using
**im_embed(3)**
in mode 1 (replicating edge pixels) just enough so that the output can match
the input.

The output at each point is divided by scale and then the offset is added. Both offset and scale are held in mask.

**im_maxvalue()**
is a convenience function: it is simply:

im_rank_image( in, out, n, n - 1 )

**im_compass()**
convolves each point of the input byte image pointed by in with 8 masks.
The first mask is the entered mask and the seven remaining masks are produced
by successive rotations of the entered mask by 45 degrees. The maximum output
of all masks at each point is written to the output integer IMAGE descriptor.
The function expects as input a square mask of odd size.

**im_lindetect()**
convolves each point of the input byte image pointed by in with 4 masks.
The first mask is the entered mask and the three remaining masks are produced
by successive rotations of the entered mask by 45 degrees. The maximum output
of all masks at each point is written to the output integer IMAGE descriptor.
The function expects as input a square mask of odd size.

**im_gradient()**
convolves each point of the input byte image pointed by in with 2 masks;
the entered mask and with a 90 degrees rotation of the
entered mask. If g1, g2 are the result of each convolution then for each point
abs(g1) + abs(g2) is written to the output integer IMAGE descriptor.
The function expects as input a square mask of any size.

## RETURN VALUE

All functions returns 0 on success and -1 on error.## COPYRIGHT

N. Dessipris

## AUTHOR

N. Dessipris - 02/05/1991