roifill

(Not recommended) Fill in specified region of interest (ROI) polygon in grayscale image

roifill is not recommended. Use regionfill instead. If you want to define the polygon interactively with regionfill, then use regionfill either with roipoly or with drawpolygon followed by createMask.

Syntax

J = roifill

J = roifill(I)

J = roifill(I,mask)

J = roifill(I,xi,yi)

J = roifill(x,y,I,xi,yi)

[J,BW] = roifill(___)

[x2,y2,J,BW,xi2,yi2] = roifill(___)

roifill(___)

Description

Use the roifill function to fill in a specified region of interest (ROI) polygon in a grayscale image. roifill smoothly interpolates inward from the pixel values on the boundary of the polygon by solving Laplace's equation. The boundary pixels are not modified. roifill can be used, for example, to erase objects in an image.

J = roifill creates an interactive polygon selection tool associated with the image displayed in the current figure. With this syntax and the other interactive syntaxes, the polygon selection tool blocks the MATLAB^® command line until you complete the operation. roifill fills the selected polygon and returns the filled image, J.

For more information about using the polygon selection tool to define and fill ROIs, see Interactive Behavior.

J = roifill(I) displays the image I in a figure window and creates an interactive polygon tool associated with the image.

J = roifill(I,mask) fills regions in I corresponding to the nonzero pixels in the mask. If there are multiple regions, then roifill performs the interpolation on each region independently.

J = roifill(I,xi,yi) fills in the polygon with vertices defined by X-Y coordinates xi and yi in the default spatial coordinate system.

J = roifill(x,y,I,xi,yi) defines a nondefault spatial coordinate system using the vectors x and y. The polygon vertices have coordinates xi and yi in this coordinate system.

[J,BW] = roifill(___) returns the binary image BW with 1s for pixels corresponding to the interpolated region of I and 0s elsewhere.

[x2,y2,J,BW,xi2,yi2] = roifill(___) also returns the image XData and YData in x2 and y2 and the polygon coordinates in xi2 and yi2.

roifill(___) without an output argument displays the filled image in a new figure window.

Examples

Fill Region in Grayscale Image

Read and display a grayscale image.

I = imread('eight.tif');
imshow(I)

Specify the x- and y-coordinates of a polygon that completely surrounds one of the coins in the image.

x = [222 272 300 270 221 194];
y = [21 21 75 121 121 75];

Fill the polygon by using the regionfill function.

J = regionfill(I,x,y);

Display the filled image.

imshow(J)
title('Filled Image with One Fewer Coin')

Input Arguments

I — Grayscale image

numeric matrix

Grayscale image, specified as a numeric matrix.

Data Types: single | double | int16 | uint8 | uint16

mask — Mask

numeric matrix | logical matrix

Mask, specified as a numeric or logical matrix of the same size as the input image, I.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical

xi, yi — x- or y-coordinate of vertices

numeric vector

x- or y-coordinate of polygon vertices, specified as numeric vectors of equal length. If you specify a nondefault coordinate system using the x and y arguments, then xi and yi specify coordinates in this coordinate system. Otherwise, xi and yi specify coordinates in the default coordinate system.

x, y — Image extent in world coordinates

2-element numeric vector

Image extent in world X-Y coordinates, specified as a 2-element numeric vector of the form [min max]. The two elements of x give the x-coordinates (horizontal) of the first and last columns of image I, respectively. The two elements of y give the y-coordinates (vertical) of the first and last rows of I.

Output Arguments

J — Filled image

numeric matrix

Filled image, returned as a numeric matrix.

Data Types: single | double | int16 | uint8 | uint16

BW — Binary image

logical matrix

Binary image, returned as a logical matrix of the same size as the input image, I.

Data Types: logical

xi2, yi2 — x- or y-coordinate of vertices

numeric vector

x- or y-coordinate of polygon vertices, specified as numeric vectors. xi and yi are empty if you specify the polygon ROI using the mask argument.

x2, y2 — Image extent in world coordinates

2-element numeric vector

Image extent in world X-Y coordinates,, returned as 2-element numeric vectors of the form [min max]. If you specify image limits x and y, then x2 and y2 are equal to these values. Otherwise, x2 and y2 are equal to the original image XData and YData.

More About

Interactive Behavior

When you call roifill with an interactive syntax, a polygon selection tool opens that enables you to select and adjust polygon vertices interactively using the mouse.

When the polygon tool is active, the pointer changes to cross hairs when you move the pointer over the image in the figure. Using the mouse, specify the region by selecting vertices of the polygon. You can move or resize the polygon using the mouse. When you are finished positioning and sizing the polygon, fill the polygon by double-clicking, or by right-clicking inside the region and selecting Fill Area from the context menu.

The figure illustrates a polygon defined by multiple vertices.

Interactive Behavior	Description
Closing the polygon (completing the ROI)	Use any of the following mechanisms: Move the pointer over the initial vertex of the polygon that you selected. The shape 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 and draws a straight line connecting this vertex with the initial vertex. Click the right mouse button. This action draws a line connecting the last vertex selected with the initial vertex; it does not create a new vertex.
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 the polygon	Move the pointer inside the region. The pointer changes to a fleur . Click and drag the mouse to move the polygon.
Changing the color of the polygon	Move the pointer inside the region. Right-click and select Set color from the context menu.
Adding a new vertex	Move the pointer over an edge of the polygon and press the A key. The shape of the pointer changes . Click the left mouse button to create a new vertex at that position on the line.
Moving a vertex (reshaping the ROI)	Move the pointer over a vertex. The pointer changes to a circle . Click and drag the vertex to its new position.
Deleting a vertex	Move the pointer over a vertex. The pointer changes to a circle . Right-click and select Delete Vertex from the context menu. This action deletes the vertex and adjusts the shape of the polygon, drawing a new straight line between the two vertices that were neighbors of the deleted vertex.
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. Position is an n-by-2 array containing the x- and y-coordinates of each vertex, where n is the number of vertices you selected.

Version History

Introduced before R2006a