% x = ExtractCoordinates(file, minsize, threshold, crop, rotate, first, last)
%
% Calculates droplet position as a function of time from oscillation video. 
%
% Required input parameters:
%   file = Video file
%   minsize = Minimum size of the searched area in pixels (e.g. 100)
%   threshold = Threshold for black-and-white conversion (0..1)
%   crop = Amount video is cropped from bottom. Used to discard substrate
%          from analysis. 
% Optional input parameters:
%   rotate = Video rotation angle (deg). Used to straighten skewed videos.
%   first = First frame to be included in the analysis
%   last = Last frame to be included in the analysis
%
% Output parameters:
%   x = Resolved droplet coordinates.
%
% The function searches for areas of black pixels in the frames exceeding
% minsize and calculates x-coordinate of the center of the area. In the end
% the coordinates are plotted. Frames can contain only one object in the
% specified size range. If there are multiple objects, the returned
% coordinate is -2. If no object was found, the returned coordinate is -1.
% At the beginning of video the droplet might not be compeletely visible
% and the first coordinates show value -1. This is ok, these coordinates
% will be discarded later. If negative values appear in the middle of
% oscillation, something is wrong. You can try increasing minsize or making
% the video brighter/darker.

function x = ExtractCoordinates(varargin)

% Read input parameters
file = varargin{1};
minsize = varargin{2};
threshold = varargin{3};
crop = varargin{4};
if length(varargin) > 4
    rotate = varargin{5};
else 
    rotate = 0;
end
if length(varargin) > 5
    first = varargin{6};
else
    first = 1;
end
if length(varargin) > 6
    last = varargin{7};
else
    last = -1;  % Will be checked later
end

% Open video
video=VideoReader(file);

% Check the number of frames if needed
if last == -1 || last>video.NumberOfFrames
    last = video.NumberOfFrames;   
end

xcount=1;     % counts coordinates
xcountmax=last-first+1; % number of coordinates
count=0;
x=zeros(1,xcountmax); % reserve memory for coordinates

while(xcount <= xcountmax)
  frame=xcount+first-1;
  % Find the x-coordinate
  x(xcount)=ImageRecognition(read(video, frame),minsize,threshold,crop,rotate,0);
  
  % Delete previously printed line on screen
  fprintf(1, repmat('\b',1,count));
  
  % Check for errors
  if x(xcount)==-2
    disp('');
    disp(['Error: Several "droplets" found in frame ' num2str(frame) '! Try increasing minsize or make the video brighter.']);
    figure;
    ImageRecognition(read(video, frame),minsize,threshold,crop,rotate,1);
    return
  end
  count = fprintf('Coordinates solved: %i/%i',xcount, xcountmax);
  xcount=xcount+1;
end
fprintf('\n'); 

% Plot the coordinates
figure;
plot(x,'k.');
xlabel('t (ms)');
ylabel('x (pixels)');

end