bwpack (Image Processing Toolbox User's Guide)

Image Processing Toolbox User's Guide

Pack binary image

Syntax

```
BWP = bwpack(BW)
```

Description

BWP = bwpack(BW) packs the uint8 binary image BW into the uint32 array BWP, which is known as a packed binary image. Because each 8-bit 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.

bwpack processes the 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.

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, the functions use a specialized routine to perform the operation faster.

bwunpack is used to unpack packed binary images.

Class Support

BW can be logical or numeric, and it must be 2-D, real, and nonsparse. BWP is of class uint32.

Example

Pack, dilate, and unpack a binary image:

BW = imread('text.png');
BWp = bwpack(BW);
BWp_dilated = imdilate(BWp,ones(3,3),'ispacked');
BW_dilated = bwunpack(BWp_dilated, size(BW,1));

See Also

bwunpack, imdilate, imerode

bwmorph bwperim