analyze_raw_data.m

%
% Process captures of raw capacitance values, and plot the mutual capacitance images.
%
% Assumes that the user previously
% 1) captured a number of background mutual capacitance images (with nothing on
%    the touch screen):
%    for var in $(seq 1 10) ; do ./dump_raw_data.sh > background_$var.raw ; done
%
% 2) Captured a number of forground mutual capacitance images:
%    for var in $(seq 1 1000) ; do ./dump_raw_data.sh > frame_$var.raw ; done
%
% Will perform the following with that data
% 1) Calculate the average background intensity.
% 2) Normalize the intensities in each frame (individually) to fully span from
%    black (lowest mutual capacitance) to white (highest mutual capacitance).
% 3) Plot the result, as well as save it to disk
%
%
% Original author Simon Gustafsson (www.optisimon.com)
%
% Copyright (c) 2016 Simon Gustafsson (www.optisimon.com)
%
% Do whatever you like with this code, but please refer to me as the original author.
%

page_screen_output(0)

% Background capacitance values
bg_files_unsorted = glob("background_*.raw");

% Foreground capacitance values
fg_files_unsorted = glob("frame_*.raw");

% Number of rows and columns in the capacitance matrix to use
w = 12
h = 22


% Assumes filenames named similar to "background_5.raw"
% (underscore before number, and dot after number)
function output = customNumericSort(input)
  tmp = [];
  for n = 1:size(input, 1)
    fname = input{n};
    numAsStr = strsplit(fname, {'_', '.' })(2){};
    num = str2num(numAsStr);
    tmp = [tmp; num];
  end
  [_, index] = sort(tmp);
  for n = 1:size(input, 1)
    output{n,1} = input{index(n)};
  end
endfunction


bg_files = customNumericSort(bg_files_unsorted)
fg_files = customNumericSort(fg_files_unsorted)


%
% Read raw capacitance values from dump file.
%
% A dumpfile (generated by dump_raw_data.sh) contains a number of lines similar to this one:
% 0x2153 0x2114 0x2191 0x2195 0x20c7 0x2057 0x20b6 0x21c3 0x20ba 0x207c 0x2065 0x213d 
%
function out = readRawData(filename)
  f = fopen(filename, 'r');
  out = [];
  while (line = fgets(f)) ~= -1
	data = sscanf(line, "%x")';
	out = [ out; data];
  endwhile
  fclose(f);
endfunction


%
% Normalize in to span values between 0 and 1.
%
function out = normalize(in)
  span = max(in(:)) - min(in(:));
  out = (in - min(in(:))) ./span;
endfunction

%
% Average all the background samples
%
avg_bg = zeros(h, w);
for n = 1:size(bg_files, 1)
  fname = bg_files{n};
  X = readRawData(fname)(1:h, 1:w);
  avg_bg = avg_bg + X;
end
avg_bg = avg_bg / size(bg_files,1)

%
% Blow up the size of the image (using nearest neighbor)
%
function out = expand(in, factor)
  out = imresize(in, factor, 'nearest');
endfunction

%
% playback all the forground samples
%
global_max = -Inf;
global_min = Inf;
for n = 1:size(fg_files, 1)
  fname = fg_files{n};
  
  raw = readRawData(fname)(1:h, 1:w);
  X = raw - avg_bg;
  
  %
  % Draw the capacitance image in a plot window
  %
  imagesc(X);
  sleep(0.01);
  
  global_max = max([global_max; X(:)]);
  global_min = min([global_min; X(:)]);
  
  % Normal way of normalizing each frame individually
  img = normalize(X);
  
  % Test normalizing all frames to the same amplitude
  % (coefficients needs to have been determined in an earlier run)
  %img = (X - (-163.83) + 0.01) / (386.44 - (-163.83) + 0.02);
  
  %
  % Save an up-scaled version of the capacitance image to disk.
  %
  out_fname = sprintf("out_%06d.png", n)
  imwrite(expand(img, 32), out_fname)
end

% Print global max and min capacitance value (after background correction)
global_max
global_min