bwpack

Pack binary image

Syntax

BWP = bwpack(BW)

Description

BWP = bwpack(BW) packs the binary image BW into the uint32 array BWP, which is known as a packed binary image. Because each pixel value in the binary image has only two possible values, 1 and 0, bwpack can map each pixel to a single bit in the packed output image.

Examples

Pack, Dilate, and Unpack Binary Image

Read binary image into the workspace.

BW = imread('text.png');
imshow(BW)

Pack the image.

BWp = bwpack(BW);

Dilate the packed image.

BWp_dilated = imdilate(BWp,ones(3,3),'ispacked');

Unpack the dilated image and display it.

BW_dilated = bwunpack(BWp_dilated, size(BW,1));
imshow(BW_dilated)

Input Arguments

BW — Binary image

2-D numeric matrix | 2-D logical matrix

Binary image, specified as a 2-D numeric or logical matrix. 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

Output Arguments

BWP — Packed binary image

numeric matrix

Packed binary image, returned as a numeric matrix of type uint32.

Data Types: uint32

Tips

• Binary image packing is used to accelerate some binary morphological operations, such as dilation and erosion. If the input to imdilate or imerode is a packed binary image, then the function uses a specialized routine to perform the operation faster.

• Use bwunpack to unpack packed binary images.

Algorithms

bwpack processes the input image pixels by column, mapping groups of 32 pixels into the bits of a uint32 value. The first pixel in the first row corresponds to the least significant bit of the first uint32 element of the output array. The first pixel in the 32nd input row corresponds to the most significant bit of this same element. The first pixel of the 33rd row corresponds to the least significant bit of the second output element, and so on. If BW is M-by-N, then BWP is ceil(M/32)-by-N. This figure illustrates how bwpack maps the pixels in a binary image to the bits in a packed binary image.

Extended Capabilities

C/C++ Code Generation

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

Usage notes and limitations:

• bwpack supports the generation of C code (requires MATLAB^® Coder™). The code generated for bwpack 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 Types of Code Generation Support in Image Processing Toolbox.

Thread-Based Environment

Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool.

This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

Version History

Introduced before R2006a

R2022b: Support for thread-based environments

bwpack now supports thread-based environments.