# Edge detection

Apply different types of edge detection methods to different types of images.

## Goals

To evaluate line detection accuracy using Hough transform.

# Images and Edges

## Images     ## Edge detection

### Matlab script

``````%Load Image

%Convert image to grayscal

B=rgb2gray(I);

%Find edges using the Canny method.
BWC = edge(B,'Canny');

%Find edges using the Sobel method.
BWP = edge(B,'Sobel');

%Display both results side-by-side.
imshowpair(BWC,BWP,'montage

``````

## Results     ## Summary

In photos with many objects - low contrast, the best methods for showing the edges of objects are canny. In higher contrast photos, the edge of objects is best detected by the sobel method.

# Lines

## Script

``````
B=rgb2gray(I);
BW = edge(B,'method');

[H,theta,rho] = hough(BW);

P = houghpeaks(H,5,'threshold',ceil(0.3*max(H(:))));

lines = houghlines(BW,theta,rho,P,'FillGap',5,'MinLength',7);

``````
``````figure, imshow(I), hold on
max_len = 0;
for k = 1:length(lines)
xy = [lines(k).point1; lines(k).point2];
plot(xy(:,1),xy(:,2),'LineWidth',2,'Color','green');

% Plot beginnings and ends of lines
plot(xy(1,1),xy(1,2),'x','LineWidth',2,'Color','yellow');
plot(xy(2,1),xy(2,2),'x','LineWidth',2,'Color','red');

% Determine the endpoints of the longest line segment
len = norm(lines(k).point1 - lines(k).point2);
if ( len > max_len)
max_len = len;
xy_long = xy;
end
end
% highlight the longest line segment
plot(xy_long(:,1),xy_long(:,2),'LineWidth',2,'Color','red');

``````

## Results

### Sobel     ### Roberts     ### log     Categories:

Updated: