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function [ gammaTable1, gammaTable2, displayBaseline, displayRange, displayGamma ] = CalibrateMonitorPhotometer( numMeasures )
% [gammaTable1, gammaTable2, displayRange. displayGamma] =
% CalibrateMonitorPhotometer(numMeasures)
% A simple calibration script for analog photometers. numMeasures (default: 9)
% readings are taken manually, and the readings are fit with a gamma function
% and piecewise cubic splines. numMeasures - 1 should be a power of 2, ideally (9, 17, 33, etc.).
% The corresponding linearized gamma tables (1 -> gamma,
% 2 -> splines) are returned, as well as the display baseline, display range in cd/m^2 and
% display gamma. Plots of the two fits are created as well. Requires fit
% tools.
%
% If the normalized gamma table is not loaded, then the cd/m^2 value of a
% screen value can be figured out by the formula: cdm2 =
% displayRange*(screenval/255).^(1/displayGamma) + displayBaseline.
%
% Generally, you will want to load the normalized gamma tables and use them
% in Screen('LoadNormalizedGammaTable'). For example:
%
% [gammaTable1, gammaTable2] = CalibrateMonitorPhotometer;
% %Look at the outputted graphs to see which one gives a better fit
% %Then save the corresponding gamma table for later use
% gammaTable = gammaTable1;
% save MyGammaTable gammaTable
%
% %Then when you're ready to use the gamma table:
% load MyGammaTable
% Screen('LoadNormalizedGammaTable', win, gammaTable*[1 1 1]);
%
%
% History:
% Version 1.0: Patrick Mineault (patrick.mineault@gmail.com)
% 22.10.2010 mk Switch numeric input from use of input() to use of
% GetNumber(). Restore gamma table after measurement. Make
% more robust.
global vals;
global inputV;
if(nargin < 1)
numMeasures = 9;
end
input(sprintf(['When black screen appears, point photometer, \n' ...
'get reading in cd/m^2, input reading using numpad and press enter. \n' ...
'A screen of higher luminance will be shown. Repeat %d times. ' ...
'Press enter to start'], numMeasures));
origclut = repmat([0:255]'/255,1,3); %#ok<NBRAK>
psychlasterror('reset');
try
win = Screen('OpenWindow', 0, 0);
BackupCluts;
Screen('LoadNormalizedGammaTable', win, origclut );
vals = [];
inputV = [0:256/(numMeasures - 1):256]; %#ok<NBRAK>
inputV(end) = 255;
for i = inputV
Screen('FillRect',win,i);
Screen('Flip',win);
% MK: Deprecated as not reliable: resp = input('Value?');
fprintf('Value? ');
resp = GetNumber;
fprintf('\n');
vals = [vals resp]; %#ok<AGROW>
end
RestoreCluts;
Screen('CloseAll');
catch
RestoreCluts;
Screen('CloseAll');
psychrethrow(psychlasterror);
end
displayRange = (max(vals) - min(vals));
displayBaseline = min(vals);
%Normalize values
vals = (vals - displayBaseline)/(max(vals) - min(vals));
inputV = inputV/255;
if ~exist('fittype'); %#ok<EXIST>
fprintf('This function needs fittype() for automatic fitting. This function is missing on your setup.\n');
fprintf('Therefore i can''t proceed, but the input values for a curve fit are available to you by\n');
fprintf('defining "global vals;" and "global inputV" on the command prompt, with "vals" being the displayed\n');
fprintf('values and "inputV" being user input from the measurement. Both are normalized to 0-1 range.\n\n');
error('Required function fittype() unsupported. You need the curve-fitting toolbox for this to work.\n');
end
%Gamma function fitting
g = fittype('x^g');
fittedmodel = fit(inputV',vals',g);
displayGamma = fittedmodel.g;
gammaTable1 = ((([0:255]'/255))).^(1/fittedmodel.g); %#ok<NBRAK>
firstFit = fittedmodel([0:255]/255); %#ok<NBRAK>
%Spline interp fitting
fittedmodel = fit(inputV',vals','splineinterp');
secondFit = fittedmodel([0:255]/255); %#ok<NBRAK>
figure;
plot(inputV, vals, '.', [0:255]/255, firstFit, '--', [0:255]/255, secondFit, '-.'); %#ok<NBRAK>
legend('Measures', 'Gamma model', 'Spline interpolation');
title(sprintf('Gamma model x^{%.2f} vs. Spline interpolation', displayGamma));
%Invert interpolation
fittedmodel = fit(vals',inputV','splineinterp');
gammaTable2 = fittedmodel([0:255]/255); %#ok<NBRAK>
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