Specify polygonal region of interest (ROI)
BW = roipoly
BW = roipoly(I)
BW = roipoly(I, c, r)
BW = roipoly(x, y, I, xi, yi)
[BW, xi, yi] = roipoly(...)
[x, y, BW, xi, yi] = roipoly(...)
roipoly to specify a polygonal region
of interest (ROI) within an image.
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
roipoly returns the mask as a binary image,
the same size as
I. In the mask image,
pixels inside the region to
1 and pixels outside
the region to
|Closing the polygon. (Completing the region-of-interest.)|
Use any of the following mechanisms:
|Moving the entire polygon||Move the pointer inside the region. The pointer changes to a fleur shape . Click and drag the polygon over the image.|
|Deleting the polygon|
Press 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
Right-click and select Delete vertex from
the context menu. |
|Changing the color of the polygon||Move 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.|
If you call
roipoly without specifying any
roipoly displays the resulting
mask image in a new figure window.
BW = roipoly(I) displays
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
which specify the column and row indices of each vertex, respectively.
be the same size.
BW = roipoly(x, y, I, xi, yi) uses
y to establish
a nondefault spatial coordinate system.
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
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
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
yi is one
greater than the number of points specified.)
[x, y, BW, xi, yi] = roipoly(...) returns
the mask image in
BW, and the polygon coordinates
The input image
I can be of class
double. The output image
logical. All other inputs and outputs
are of class
roipoly to create a mask image,
the same size as the input image,
I. The example
roifilt2 continues this example, filtering the
specified region in the image. To see another example of using
especially of the interactive syntaxes, see Fill Region of Interest in an Image.
Read an image into the workspace.
I = imread('eight.tif');
Define the vertices of the mask polygon.
c = [222 272 300 270 221 194]; r = [21 21 75 121 121 75];
Create the binary mask image.
BW = roipoly(I,c,r);
Display the original image and the polygonal mask.
For any of the
roipoly syntaxes, you can
replace the input image
I with two arguments,
that specify the row and column dimensions of an arbitrary image.
For example, these commands create a 100-by-200 binary mask.
c = [112 112 79 79]; r = [37 66 66 37]; BW = roipoly(100,200,c,r);
If you specify
an interactive form of
image is displayed, and you use the mouse to specify a polygon within