what is the meaning of this line? BW = im2bw(GRAY, threshold);

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 this line?

BW = im2bw(GRAY, threshold);

Answer 1

[Iain]

That line compares your image, to a threshold, and produces an array of the same size, containing "false" where the image is less than the threshold, and "true" where it is higher than it.

If you do not recognise a function, I recommend looking it up in matlab's help rather than asking here - you'll get faster answers.