**FREI_CHEN_ED_CVIP**

**frei_chen_ed_cvip()** - Performs Frei-Chen Edge detection on an image.

## Contents

## SYNTAX

[ M , cos_theta] = frei_chen_ed_cvip( input_img, subspace )

Input Parameters include:

- input_img - The input image. Can be multiband.
- subspace - '1' for edge subspace. '2' for line subspace. '3' for average subspace.

Output Parameter includes :

- [ M , cos_theta] - Magnitude and phase of the output image after frei_chen edge detection.

## DESCRIPTION

Frei-chen is one type of edge detector in which masks are unique. They form a complete set of basis vectors. Any 3*3 subimage can be represented as a weighted sum of the nine Frei-chen masks. These weights are found by projecting 3*3 subimages on to each of these masks. Frie-chen masks can be grouped in to a set of four masks for an edge subspace,four masks for a line subspace, and one mask for an average subspace. These subspaces can be broken down in to gradient, ripple, line and laplacian subspace.

## REFERENCE

1. Scott E Umbaugh. DIGITAL IMAGE PROCESSING AND ANALYSIS: Applications with MATLAB and CVIPtools, 3rd Edition.

## EXAMPLE

% Read image input_img = imread('butterfly.tif'); % Average Sub space [ M, cos_th ] = frei_chen_ed_cvip( input_img, 3 ); % Display input image figure;imshow(input_img);title('Input Image'); % Display output image figure; imshow(hist_stretch_cvip(M , 0,1,0,0),[]);title('Output Image after frei chen edge detection'); figure; imshow(hist_stretch_cvip(cos_th , 0,1,0,0));title('Output Image after frei chen edge detection');

## CREDITS

Author: Mehrdad Alvandipour, July 2017

Copyright © 2017-2018 Scott
E Umbaugh

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