Semivar

Purpose

Calculates semivariance for texture analysis.

Synopsis

[y,s] = semivar(x,s,options)

Description

SEMIVAR calculates the semivariance similar to that used in Kriging, and can be used to characterize texture for the input (x) which is an m by n matrix (e.g. an image layer). The (y) a cell with each element containing a vector of the sqrt(semivariance) and (s) a cell with the associated distance vectors (in pixels). Each cell element corresponds to the semivariance calculated for 4 directions

• y{1}, s{1} is down the rows (top-to-bottom),
• y{2}, s{2} is down the columns (left-to-right),
• y{3}, s{3} is diagonal (upper left-to-bottom right), and
• y{4}, s{4} is diagonal (upper right-to-bottom left).

The semivariance is defined as: with larger semivariance indicating less correlation. Optional input (s) is a 2 element cell containing the distances (in pixels) measures to be calculated. Each cell contains a vector of integers defining the distance in pixels for the rows and columns respectively. Defaults:

• s{1} = 1:floor(m/2); s{3} = s{1}\*sqrt(2);
• s{2} = 1:floor(n/2); s{4} = s{1}\*sqrt(2);

options is a structure discussed below.

Options

options is a structure is a structure array with the following fields:

• flag: [ 'off' | {'on'} ] when set to 'off' the function only calculates the first two semivariances (top-to-bottom and left-to-right). This is faster when (x) is large.
• plots: [ 'none' | {'final'} ] governs level of plotting,

See Also

autocor_img, detrend_img, fft_texture, svd_texture, texture