cc2bw

Convert connected components to binary image

Since R2024a

Syntax

BW = cc2bw(CC)

BW = cc2bw(CC,ObjectsToKeep=objectsToKeep)

Description

BW = cc2bw(CC) creates a binary image from the connected components (objects) in CC.

BW = cc2bw(CC,ObjectsToKeep=objectsToKeep) creates a binary image from a subset of connected components, specified by objectsToKeep.

Examples

Filter on Multiple Image Properties

Read and display an image.

I = imread("blobs.png");
imshow(I)

Create a connected components structure.

CC = bwconncomp(I);

Filter the structure and keep round objects. Display the filtered image.

CC = bwpropfilt(CC,"Circularity",[0.7 1]);
imshow(cc2bw(CC))

Filter the structure again and keep large objects. Display the filtered image.

CC = bwpropfilt(CC,"Area",[20 Inf]);
imshow(cc2bw(CC))

Create Binary Image with Subset of Filtered Objects

Read a binary image and detect the connected components.

BW = imread("text.png");
CC = bwconncomp(BW);

Measure the area of each connected component and return the results as a table.

p = regionprops("table",CC,"Area");

Create a binary image that contains only the 2nd through 10th largest connected components. Display the result.

[~,idx] = sort(p.Area,"descend");
BWfilt = cc2bw(CC,ObjectsToKeep=idx(2:10));
imshow(BWfilt)

Isolate Vertically Oriented Regions

Read a grayscale image of grains of rice, then convert the image to binary.

I = imread("rice.png");
BW = imbinarize(I);
imshow(BW)

Measure the area and bounding box of each region.

CC = bwconncomp(BW); 
stats = regionprops("table",CC,"Area","BoundingBox");

Select regions for whom these conditions apply:

• The area is greater than 50 pixels

• The bounding box is less than 15 pixels wide and is greater than or equal to 20 pixels tall.

area = stats.Area;
bbox = stats.BoundingBox;
selection = (area > 50) & (bbox(:,3) < 15) & (bbox(:,4) >= 20);
BW2 = cc2bw(CC,ObjectsToKeep=selection);

Display the filtered image.

imshow(BW2)

Input Arguments

CC — Connected components

structure

Connected components (objects), specified as a structure with four fields.

Field	Description
Connectivity	Connectivity of the connected components
ImageSize	Size of the binary image
NumObjects	Number of connected components in the binary image.
PixelIdxList	1-by-NumObjects cell array where the k-th element in the cell array is a vector containing the linear indices of the pixels in the k-th object.

objectsToKeep — Objects to keep

positive integer | vector of positive integers | logical vector

Objects to keep, specified as one of these values.

• Positive integer or vector of positive integers — Keep the object or objects whose index is included in objectsToKeep. The length of objectsToKeep is less than or equal to CC.NumObjects.

• Logical vector — Keep the objects whose corresponding element in objectsToKeep is true. The length of objectsToKeep must be equal to CC.NumObjects.

Output Arguments

BW — Binary image

logical array

Binary image, returned as a logical array of the same size as CC.ImageSize.

Data Types: logical

Extended Capabilities

C/C++ Code Generation

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

Usage notes and limitations:

• cc2bw supports the generation of C code (requires MATLAB^® Coder™). For more information, see Code Generation for Image Processing.

• If you generate code for the cc2bw function directly, then CC.PixelIdxList must be homogeneous. This code shows how to make CC.PixelIdxList homogeneous by using the makeHomogeneous (MATLAB Coder) function.

  CC = bwconncomp(BW);
  CC2 = bwpropfilt(CC,"Area",10);
  typeCC = coder.typeof(CC2);
  typeCC.Fields.PixelIdxList = makeHomogeneous(typeCC.Fields.PixelIdxList);
  
  codegen cc2bw -args {typeCC}

  If you generate code for a wrapper function, then you do not need to make CC.PixelIdxList homogeneous. For example, this command generates code for a wrapper function named myFunction.

  codegen myFunction -args {BW}

  Here is a sample definition for the wrapper function myFunction that includes a call to the cc2bw function.

  function out = myFunction(BW) %#codegen
      CC = bwconncomp(BW);
      CC2 = bwpropfilt(CC,"Area",10);
      out = cc2bw(CC2);
  end

Version History

Introduced in R2024a

R2024a: Generate C code using MATLAB Coder

cc2bw now supports the generation of C code (requires MATLAB Coder).