MATLAB: Compressing a logical array into a bit-wise boolean representation

booleanbwpackImage Processing Toolboxlogical?

Standard MATLAB logical arrays use 1 byte to represent each boolean element in the array. However, I seem to remember coming across a way, maybe in the Image Processing Toolbox, to convert a logical array to a representation that uses only 1 bit per boolean. My recollection is fuzzy, but can anyone recognize what I'm referring to and, if so, point me to the appropriate doc?

Best Answer

may be bwpack is function you are looking.

from help.

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.

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MATLAB: 3×3 8-connected structuring element

If you use a integer or double class, it's

1  1  1
1  1  1
1  1  1

which is the same as

se = ones(3); % <= double, or:
se = ones(3, 'uint8'); % <= uint8

or for a logical / boolean class:

true true true
true true true
true true true

which is the same as

se = true(3);

You can also use the strel function

se = strel('disk', 5);

where se is a special class of type 'strel'.

I usually use the logical form when I make up a structuring element manually.

MATLAB: Thresholding and Binarising and doubling

Hi Yasasween,

In the statement b,

b=im2bw(a,155/255);

b = im2bw(I,level) “im2bw” produces binary images from indexed, intensity, or RGB images. To do this, it converts the input image to grayscale format (if it is not already an intensity image), and then uses thresholding to convert this grayscale image to binary. The output binary image has values of 1 (white) for all pixels in the input image with luminance greater than level and 0 (black) for all other pixels.

im2bw is not recommended. Use imbinarize instead. The default luminance threshold of im2bw is not optimal for most images.

You can use the imbinarize, do the thresolding convert it to a binary image.

In the statement c,

c=a>155

It just returns a logical array with elements set to logical 1 (true) where A is greater than B; otherwise, the element is logical 0 (false). The test compares only the real part of numeric arrays. gt returns logical 0 (false) where A or B have NaN or undefined categorical elements.

In the statement d,

d=double(a)

double converts symbolic values to MATLAB double precision, so here it converts from uint8 to double type.

Hope this Helps!

Best Answer

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MATLAB: 3×3 8-connected structuring element

MATLAB: Thresholding and Binarising and doubling

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