what is the meaning of BW = ~ BW?

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Shaila parvin
Shaila parvin 2013-5-28
function [shape] = Classify(ImageFile)
if ndims(imread(ImageFile))>2
RGB = imread(ImageFile);
GRAY = rgb2gray(RGB);
else
GRAY=imread(ImageFile);
%RGB=GRAY;
end
threshold = graythresh(GRAY);
BW = im2bw(GRAY, threshold);
%Invert the Binary Image
BW = ~ BW;
[~,L] = bwboundaries(BW, 'noholes');
STATS = regionprops(L,'all');
for i=1:length(STATS)
if norm([STATS(i).Extrema(2,1), STATS(i).Extrema(2,2)]-[STATS(i).Extrema(1,1), STATS(i).Extrema(1,2)])<5 %TR,TL
%can be triangle hexagon pentagon
if norm([STATS(i).Extrema(4,1), STATS(i).Extrema(4,2)]-[STATS(i).Extrema(3,1), STATS(i).Extrema(3,2)])<5 %RT,RB
%can be pentagon triangle
if norm([STATS(i).Extrema(4,1), STATS(i).Extrema(4,2)]-[STATS(i).Extrema(5,1), STATS(i).Extrema(5,2)])<5 %RT,RB,BR = Triangle
shape(i,1)=1; % Triangle
else
shape(i,1)=3; % Pentagon
end
else
shape(i,1) = 4; % hexagon
end
elseif (STATS(i).MajorAxisLength/STATS(i).MinorAxisLength<1.1 && STATS(i).Eccentricity <0.5 || (STATS(i).Solidity/STATS(i).Extent)==1)&(STATS(i).Area<0.1*numel(GRAY))
shape(i,1)=2; % Rectangle
else
shape(i,1)=0;
end
end
if ~isempty(find(shape==2))
disp('Rectangle found');
else
disp('No rectangle in the image')
end
return
what is the meaning of
BW = ~ BW;
this line?
  1 个评论
Shaila parvin
Shaila parvin 2013-5-28
what is the meaning of this line?
BW = im2bw(GRAY, threshold);

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采纳的回答

Walter Roberson
Walter Roberson 2013-5-28
~ is logical negation in this context. If you selected one area into BW, then ~BW is everything else that was not that area. bwthresh selects areas with grey scale above a certain level; ~BW would then be everywhere with grey scale below that level. Useful if you have black letters on a light background for example.

更多回答（1 个）

John Doe
John Doe 2013-5-28
It gives you back the inverted binary matrix BW. That means, all 1's turns to 0's, and vice versa.
In plain text:
BW = not BW.
Suppose the binary image is represented as:
BW =
1 1 1 1
1 0 1 0
0 0 0 1
1 1 1 0
Then BW = ~ BW gives:
BW =
0 0 0 0
0 1 0 1
1 1 1 0
0 0 0 1
Hope this answers your question =)
- Robert
  1 个评论
Shaila parvin
Shaila parvin 2013-5-28
what is the meaning of this line?
BW = im2bw(GRAY, threshold);

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