How to automatically identify text lines from projection plot?

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I have been reading about automatic text line recognition in Matlab and although there are many advanced methods to do this every paper mentions that the simplest way of detecting text lines is via horizontal projections. So I decided to try this method for myself.
I am very new to this and have hit a brick wall, I have reached a level beyond which I do not know how to proceed. This is what I have achieved so far:
I'm trying for a system that is language independent and only interested in text lines, so I chose Arabic text:
I used the function ``radon`` to get the projections.
img = rgb2gray(imread('arabic.jpg'));
[R, xp] = radon(bw_closed, [0 90]);
figure; plot(xp,R(:,2)); title('at angle 90');
This is the plot(projection)
So clearly the 5 peaks represent the 5 lines detected but how do I go from here to segmenting the original document?
Can anyone help me beyond this point? All the papers I read make no mention of how to proceed from this step, they just say that from the projections we have our detected lines.
What I'm asking is how, from the plot data can I tell matlab what is the line of text and what is the gab between lines?
  1 Comment
VIBHATH V B on 3 Mar 2015
Hi.......... Can u send me the whole code for the above? What is 'bw-closed' here? My E-mail Id is :

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Accepted Answer

Image Analyst
Image Analyst on 18 Jan 2014
I would just find where the black is in the profile
darkPixels = R < 20; % Threshold
% label
labeledRegions = bwlabel(darkPixels);
% Find centroids
measurements = regionprops(labeledRegions, 'Centroid');
% Get them into an array
allCentroids = [measurements.Centroid];
Now you can just crop out some line of text you're interested in, into a separate image:
thisLine = yourImage(allCentroids(k):allCentroids(k+1), :);
Image Analyst
Image Analyst on 7 Aug 2018
I don't think it has a name. It's just something I thought up. Something that basic usually doesn't have a name.
Bachtiar Muhammad Lubis
Bachtiar Muhammad Lubis on 2 Dec 2018
@ HJ Akhtar : i've read some papers and found that this is projection profile algorihm. just googling "image segmentation using projection profile".

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More Answers (2)

fawzi on 25 Sep 2014
what if the lines are curved ? in this case the projection is not useful. Can you help me in this problem

Rinku on 2 Jan 2015
Edited: Walter Roberson on 19 Dec 2015
try this code;
img = rgb2gray(imread('arabic.jpg'));
[R, xp] = radon(bw_closed, [0 90]);
figure; plot(xp,R(:,2)); title('at angle 90');
r = R(:,2);
r=r(92:391); % your image region
blank = r < 3; % region without text
[labeled, n] = bwlabel(blank);
C = regionprops(labeled, 'Centroid'); % find the centers of blank regions
for i=1:length(C)-1
Urooba zaki
Urooba zaki on 22 Jan 2018
respected sir this code shows an error... i think the function file is missing ... plz reply Undefined function or variable 'bw_closed'.

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