bwselect

Select objects in binary image

Syntax

BW2 = bwselect(BW,c,r,n)

BW2 = bwselect(BW,n)

[BW2,idx] = bwselect(___)

BW2 = bwselect(x,y,BW,xi,yi,n)

[x,y,BW2,idx,xi,yi] = bwselect(___)

Description

BW2 = bwselect(BW,c,r,n) returns a binary image containing the objects that overlap the pixel (r,c), where n specifies the connectivity. Objects are connected sets of on pixels, that is, pixels having a value of 1. By default, bwselect looks for 4-connected objects.

BW2 = bwselect(BW,n) displays the image BW on the screen and lets you select the (r,c) coordinates using the mouse. If you omit BW, bwselect operates on the image in the current axes. Use normal button clicks to add points. Press Backspace or Delete to remove the previously selected point. A shift-click, right-click, or double-click selects the final point; press Return to finish the selection without adding a point.

[BW2,idx] = bwselect(___) returns the linear indices of the pixels belonging to the selected objects.

BW2 = bwselect(x,y,BW,xi,yi,n) uses the vectors x and y to establish a nondefault spatial coordinate system for BW. The arguments xi and yi are scalars or equal-length vectors that specify locations in this coordinate system.

[x,y,BW2,idx,xi,yi] = bwselect(___) returns the XData and YData in x and y, the output image in BW2, linear indices of all the pixels belonging to the selected objects in idx, and the specified spatial coordinates in xi and yi.

Examples

Select Objects in Binary Image

Select objects in a binary image and create a new image containing only those objects.

Read binary image into the workspace.

BW = imread('text.png');

Specify the locations of objects in the image using row and column indices.

c = [43 185 212];
r = [38 68 181];

Create a new binary image containing only the selected objects. This example specifies 4-connected objects.

BW2 = bwselect(BW,c,r,4);

Display the original image and the new image side-by-side.

imshowpair(BW,BW2,'montage');

Input Arguments

BW — Input binary image

2-D, nonsparse, logical or numeric matrix

Input binary image, specified as a 2-D, nonsparse, logical or numeric matrix. If you do not specify an output argument, bwselect displays the output image in a new figure.

Example: BW = imread('text.png');

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

c — Column index

numeric scalar or vector

Column index, specified as a numeric scalar or vector. If c and r are equal-length vectors, BW2 contains the sets of objects overlapping with any of the pixels (r(k),c(k)).

Example: c = [43 185 212];

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

r — Row index

numeric scalar or vector

Row index, specified as a numeric scalar or vector. If r and c are equal-length vectors, BW2 contains the sets of objects overlapping with any of the pixels (r(k),c(k)).

Example: r = [38 68 181];

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

n — Connectivity

8 (default) | 4

Connectivity, specified as either the value 4 or 8.

Value	Description
4	4-connected objects
8	8-connected objects

Example: BW2 = bwselect(BW,c,r,4);

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

x — x coordinates of nondefault coordinate system

numeric scalar or vector

x coordinates of nondefault coordinate system, specified as a numeric scalar or vector.

Example: x = [19.5 23.5];

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

y — y coordinates of nondefault coordinate system

numeric scalar or vector

y coordinates of nondefault coordinate system, specified as a numeric scalar or vector.

Example: y = [8.0 12.0];

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

xi — x coordinates of locations in nondefault coordinate system

numeric scalar or vector

x coordinates of locations in nondefault coordinate system, specified as a numeric scalar or vector.

Example: x = [19.5 23.5];

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

yi — y coordinates of locations in nondefault coordinate system

numeric scalar or vector

y coordinates of locations in nondefault coordinate system, specified as a numeric scalar or vector.

Example: y = [8.0 12.0];

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

Output Arguments

BW2 — Binary image containing objects that overlap the specified pixels

logical array

Binary image containing objects that overlap the specified pixels, returned as a logical array.

If you do not specify an output argument, bwselect displays the output image in a new figure.

idx — Linear indices of the pixels belonging to the selected objects

numeric vector

Linear indices of the pixels belonging to the selected objects, returned as a numeric vector.

Extended Capabilities

C/C++ Code Generation

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

Usage notes and limitations:

• bwselect supports the generation of C code (requires MATLAB^® Coder™). Note that if you choose the generic MATLAB Host Computer target platform, bwselect generates code that uses a precompiled, platform-specific shared library. Use of a shared library preserves performance optimizations but limits the target platforms for which code can be generated. For more information, see Code Generation Using a Shared Library.

• When generating code, bwselect only supports the following syntaxes:

  • BW2 = bwselect(BW, c, r)

  • [BW2, idx] = bwselect(BW, c, r)

  • BW2 = bwselect(BW, c, r, n)

  • [BW2, idx] = bwselect(BW, c, r, n)

• In addition, the optional fourth input argument, n, must be a compile-time constant.

GPU Code Generation

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

Usage notes and limitations:

• When generating code, bwselect only supports the following syntaxes:

  • BW2 = bwselect(BW, c, r)

  • [BW2, idx] = bwselect(BW, c, r)

  • BW2 = bwselect(BW, c, r, n)

  • [BW2, idx] = bwselect(BW, c, r, n)

• In addition, the optional fourth input argument, n, must be a compile-time constant.