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function VignettingCorrectionDemo(docolor, precision)
% Demonstrate how to do display devignetting aka per-pixel gain correction.
%
% Usage: VignettingCorrectionDemo([docolor=0][, precision=max]);
%
% 'docolor' if set to non-zero will compute and apply per-color channel
% gains instead of the default luminance gain.
%
% 'precision' selects the precision vs. speed tradeoff: 2 = max precision,
% min speed, 1 = balanced, 0 = max speed and minimum precision.
%
% Because gain correction is memory and compute intense, per-color
% correction is slower than global luminance only correction. Higher
% precisions for the definition of the gainmatrix are slower, and higher
% display resolutions are slower.
%
% The demo runs until a key is hit twice.
%
% On modern graphics cards, Psychtoolbox allows to automatically apply a
% luminance- or color gainfield to all presented stimuli. Each pixel
% location can get individually gain corrected. This is useful to correct
% for spatial luminance or color inhomogenities of display devices, e.g.,
% video projectors (due to lens vignetting effects), or flat panels (with
% their contrast and color view dependency).
%
% You need recent graphics hardware for this to work and to work at a
% decent speed.
%
% See "help PsychImaging" under subsection 'ColorCorrection' and "help
% PsychColorCorrection" under subsection 'GainMatrix' for explanation of
% the math, the parameters and other notable things of interest about gain
% correction.
%
% History:
% 6.3.2010 mk Written.
%
% Assign parameters or defaults:
if nargin < 1 || isempty(docolor)
docolor = 0;
end
if nargin < 2
precision = [];
end
% Check for properly installed Psychtoolbox:
AssertOpenGL;
% Output to max screen:
screenid = max(Screen('Screens'));
% Use imaging pipeline for visual processing and display:
PsychImaging('PrepareConfiguration');
% Request per-pixel 2D gain correction for display:
PsychImaging('AddTask', 'FinalFormatting', 'DisplayColorCorrection', 'GainMatrix');
% Open window with gray background (128 aka 50% gray), return handle 'win':
win = PsychImaging('OpenWindow', screenid, 128);
try
Screen('TextSize', win, 48);
% Build a simple luminance gain matrix, the size of the window, with a
% simple linear gradient of increasing gain values from left to right, here
% in the gain range from 0.0 to 1.5:
[width, height] = Screen('WindowSize', win);
% Test support for display gain correction:
% Try to read from default configuration file:
filename = [PsychtoolboxConfigDir('ShadingCalibration') 'VignetCalibration' sprintf('_%i_%i_%i', screenid, width, height) '.mat'];
if exist(filename, 'file')
load(filename, 'gainMatrix');
else
% gainmatrix is a linear "gain gradient" from 0.0 at the left border to
% 1.5 at the right border of the display:
gainMatrix = (meshgrid(1:width, 1:height) / width) * 1.5;
end
% If per-colorchannel correction is requested...
if docolor
% Replicate linear gains into all three color gain channels...
gainMatrix = repmat(gainMatrix, [1 1 3]);
% ... and invert the gradient in the green channel to make it
% visually more interesting:
gainMatrix(:,:,2) = (1.5 - 1.5 * meshgrid(1:width, 1:height) / width);
end
% Apply gain correction matrix to display: This will take effect at the
% next Screen('Flip'). We pass in a 'precision' flag as well, to choose
% the tradeoff between accuracy and speed:
PsychColorCorrection('SetGainMatrix', win, gainMatrix, [], precision);
KbReleaseWait;
fc = 0;
tstart = GetSecs;
% Repeat redraw loop until keypress.
while ~KbCheck
fc = fc + 1;
cl = mod(fc, 170);
% Draw a yellow oval to the screen which changes brightness periodically:
Screen('FillOval', win, [cl cl 0]);
% Text drawing is time consuming, btw...
DrawFormattedText(win, 'Hit any key twice to finish!', 'center', 'center', [0 0 128]);
% Show updated image at next refresh cycle:
Screen('Flip', win);
end
% Some stats...
fprintf('\n\nAvg redraw rate was %f Hz.\n\n', fc / (GetSecs - tstart));
% Wait for keyboard stroke before closing down...
KbStrokeWait;
% Done. Close everything down and terminate:
sca;
catch
% Usual error handling...
sca;
psychrethrow(psychlasterror);
end
return;
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