regionfill

Fill specified regions in image using inward interpolation

Syntax

J = regionfill(I,mask)

J = regionfill(I,x,y)

Description

J = regionfill(I,mask) fills the regions in image I specified by mask. Nonzero pixels in mask designate the pixels of image I to fill. You can use regionfill to remove objects in an image or to replace invalid pixel values using their neighbors.

J = regionfill(I,x,y) fills the region in image I corresponding to the polygon with vertices specified by x and y.

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')

Fill Regions Using Mask Image

Read and display a grayscale image.

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

Specify the vertices of a polygon ROI that completely surrounds two of the coins by using the drawpolygon function. Specify the 'Position' name-value pair argument as the x-coordinates and y-coordinates of the polygon vertices. If you want to draw the polygon interactively, then omit the 'Position' name-value pair argument.

x = [68 296 296 113 68];
y = [12 12 120 120 66];
roi = drawpolygon(gca,'Position',[x;y]');

Create a mask image in which the ROI is true and the background is false. Display the mask.

mask = createMask(roi);
imshow(mask)

Fill the regions in the input image using the mask image. Display the filled image.

J = regionfill(I,mask);
imshow(J)

Input Arguments

I — Grayscale image

2-D numeric matrix

Grayscale image, specified as a 2-D numeric matrix of size greater than or equal to 3-by-3.

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

mask — Mask image

logical matrix | numeric matrix

Mask image, specified as a logical matrix or numeric matrix of the same size as I. For numeric input, any nonzero pixels are considered to be 1 (true).

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

x — x-coordinates of polygon vertices

numeric vector

x-coordinates of polygon vertices, specified as a numeric vector. x must be the same length as y.

Example: [222 272 300 270 221 194];

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

y — y-coordinates of polygon vertices

numeric vector

y-coordinates of polygon vertices, specified as a numeric vector. y must be the same length as x.

Example: [21 21 75 121 121 75];

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

Output Arguments

J — Filled grayscale image

2-D numeric array

Filled grayscale image, returned as a 2-D numeric array. J has the same size and class as I.

Tips

• To interactively create the ROI mask mask, you can use the roipoly function or the drawpolygon function followed by createMask.

• For more information about how regionfill determines which pixels are on the ROI boundaries when you specify the ROI using (x, y) polygon coordinates, see Classify Pixels That Are Partially Enclosed by ROI.

Algorithms

regionfill smoothly interpolates inward from the pixel values on the outer boundary of the regions. regionfill calculates the discrete Laplacian over the regions and solves the Dirichlet boundary value problem.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

regionfill supports the generation of C code (requires MATLAB^® Coder™). For more information, see Code Generation for Image Processing.

GPU Code Generation

Generate CUDA® code for NVIDIA® GPUs using GPU Coder™.

Usage notes and limitations:

• GPU Coder™ generates optimized CUDA^® code for only the regionfill(I,mask) syntax. The regionfill(I,x,y) syntax generates code that is not optimized for GPUs.

Version History

Introduced in R2015a

R2022a: Generate CUDA code using GPU Coder

regionfill now supports the generation of optimized CUDA code (requires GPU Coder).

R2021b: Generate C code using MATLAB Coder

regionfill now supports the generation of C code (requires MATLAB Coder).