One simple way to tell different fish apart is due to their
ratio of length to width. For every species of fish, that ratio
is essentially the same. On reason salmon are unique in that
regard is because during spawning season, they grow wider and
thus their length to width ratio becomes much smaller
(approximately 2:1 or 3:1). Other fish, such as steelhead
trout, which maintain a much more sleek, approximately 3:1 to
4:1 length to width ratio even during spawning season.

This test is done using primarily the Canny Edge Detection
method which is performed by Matlab using the command `edge`

. It takes the image of the fish and
finds an outline of it.

Image edges contain strong contrasts in intensity. The Canny Edge
Detector tries to find only true edges by only selecting
localized edge points and only responding once to a single real
edge. The Canny method also filters noise with a convolution
mask built through Canny's algorithm. The edge detector then
uses the gradient of the image and summing along the x direction
and y direction to obtain the edge value. Direction of the edge
is easily determined by looking at each directions value and
seeing which one is larger. However, it is important to test for
errors when one direction is zero, so Canny looks at the angle
between the x-direction and y-direction. Canny also uses
suppression to connect values along the direction of the edge.

After the edge detection has been run, the image is binary and
all the edges are represented by ones. The rows and columns are
then each summed up. The algorithm then starts at each edge of
the image and moves toward the center until it finds a row with
a significant amount of values in it. This signals the edge of
the fish closest to that side. Then, through simple
calculations, the length, width, and ration can be calculated.

```
% This function uses canny edge detection to try to find an outline of the
% fish in the grayscale image and then it calculates the length to width
% ratio of the fish.
function [length,width,lwratio] = fishedge(image)
imagegray = rgb2gray(image);
imageedge = edge(imagegray,'canny');
l4rowedge = sum(imageedge);
l4coledge = sum(imageedge')';
l4size = size(imageedge);
j = 1;
% Find the top edge of the fish
while l4coledge(j)< 4
top = j;
j = j+1;
end
j = 1;
% Find the bottom edge of the fish
while l4coledge(l4size(1)-j+1)< 4
bottom = l4size(1)-j+1;
j = j+1;
end
width = bottom - top;
j = 1;
% Find the left edge of the fish
while l4rowedge(j)< 4
left = j;
j = j+1;
end
j = 1;
% Find the right edge of the fish
while l4rowedge(l4size(2)-j+1)%lt; 4
right = l4size(2)-j+1;
j = j+1;
end
length = right - left;
lwratio = length./width;
```

Comments:"assafdf"