roipoly() - Image Processing

Use roipoly to specify a polygonal region
of interest (ROI) within an image. roipoly returns
a binary image that you can use as a mask for masked filtering.BW = roipoly creates an interactive polygon
tool, associated with the image displayed in the current figure, called
the target image. With the polygon tool active, the pointer changes
to cross hairs 
 when you move the pointer over the
image in the figure. Using the mouse, you specify the region by selecting
vertices of the polygon. You can move or resize the polygon using
the mouse. The following figure illustrates a polygon defined by multiple
vertices. The following table describes all the interactive behavior
of the polygon tool.
When you are finished positioning and sizing the polygon, create
the mask by double-clicking, or by right-clicking inside the region
and selecting Create mask from the context
menu. roipoly returns the mask as a binary image, BW,
the same size as I. In the mask image, roipoly sets
pixels inside the region to 1 and pixels outside
the region to 0.Interactive BehaviorDescription
Closing the polygon. (Completing the region-of-interest.)Use any of the following mechanisms:Move the pointer over the initial vertex of the polygon
that you selected. The pointer changes to a circle 
. Click either mouse button.Double-click the left mouse button. This action creates
a vertex at the point under the mouse pointer and draws a straight
line connecting this vertex with the initial vertex.Right-click the mouse. This draws a line connecting
the last vertex selected with the initial vertex; it does not create
a new vertex at the point under the mouse.
Moving the entire polygonMove the pointer inside the region. The pointer changes to
a fleur shape 
.
Click and drag the polygon over the image. 
Deleting the polygonPress Backspace, Escape or Delete,
or right-click inside the region and select Cancel from
the context menu.Note: If you delete the ROI, the function
returns empty values.
Moving a vertex. (Reshaping the region-of-interest.)Move the pointer over a vertex. The pointer changes to a circle 
. Click and drag the vertex
to its new position.
Adding a new vertex.Move the pointer over an edge of the polygon and press the A key.
The pointer changes shape to
. Click the left mouse button to create
a new vertex at that point on the edge.
Deleting a vertex. (Reshaping the region-of-interest.)Move the pointer over the vertex. The pointer changes to a
circle 
.
Right-click and select Delete vertex  from
the context menu. roipoly draws a new straight
line between the two vertices that were neighbors of the deleted vertex.
Changing the color of the polygonMove the pointer anywhere inside the boundary of the region
and click the right mouse button. Select Set color from
the context menu. 
Retrieving the coordinates of the vertices Move the pointer inside the region. Right-click and select Copy
position from the context menu to copy the current position
to the Clipboard. The position is an n-by-2 array
containing the x- and y-coordinates
of each vertex, where n is the number of vertices. 
Note:  


If you call roipoly without specifying any
output arguments, roipoly displays the resulting
mask image in a new figure window.BW = roipoly(I) displays
the image I and creates an interactive polygon
tool associated with that image.BW = roipoly(I, c, r) returns
the ROI specified by the polygon described by vectors c and r,
which specify the column and row indices of each vertex, respectively. c and r must
be the same size.BW = roipoly(x, y, I, xi, yi) uses
the vectors x and y to establish
a nondefault spatial coordinate system. xi and yi are
equal-length vectors that specify polygon vertices as locations in
this coordinate system.[BW, xi, yi] = roipoly(...) returns
the x- and y-coordinates of
the polygon vertices in xi and yi. Note:  


roipoly always produces a closed polygon.
If the points specified describe a closed polygon (i.e., if the last
pair of coordinates is identical to the first pair), the length of xi and yi is
equal to the number of points specified. If the points specified do
not describe a closed polygon, roipoly adds a final
point having the same coordinates as the first point. (In this case
the length of xi and yi is one
greater than the number of points specified.)[x, y, BW, xi, yi] = roipoly(...) returns
the XData and YData in x and y,
the mask image in BW, and the polygon coordinates
in xi and yi.

Syntax

BW = roipolyBW = roipoly(I)BW = roipoly(I, c, r)BW = roipoly(x, y, I, xi, yi)[BW, xi, yi] = roipoly(...)[x, y, BW, xi, yi] = roipoly(...)

Example

I = imread('eight.tif');
c = [222 272 300 270 221 194];
r = [21 21 75 121 121 75];
BW = roipoly(I,c,r);
figure, imshow(I)
figure, imshow(BW)

Output / Return Value

Limitations

Alternatives / See Also

Reference