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function SadowskiDemo(imgName)
% SadowskiDemo([imgName]);
%
% Demonstrate Sadowski illusion on a specified image file 'imgName'. if
% 'imgName' is omitted, a default image is used.
%
% The demo will first show the color adaptation image. Please fixate the
% fixation cross in the center of the screen. Then press a key. The demo
% will show the grayscale only test image. Be amazed! Press any key to
% repeat the adaptation phase, press ESCape to quit the demo. If you press
% the left cursor key, a white test patch will be show instead of the
% luminance image.
%
% History:
% 17.03.2010 mk Written. Inspired by a demo shown by Stuart Anstis.
% Check installation:
AssertOpenGL;
KbName('UnifyKeyNames')
escape = KbName('ESCAPE');
left = KbName('LeftArrow');
% Assign our cute rabbits if image filename omitted:
if nargin < 1
imgName = [];
end
if isempty(imgName)
imgName = [PsychtoolboxRoot 'PsychDemos/konijntjes1024x768.jpg'];
end
% Read image from filesystem:
img = imread(imgName);
% Convert RGB image to HSV color space for simpler manipulation:
hsv = rgb2hsv(img);
% Extract luminance channel for pure luma image:
luma = hsv(:,:,3) * 255;
% Open window with black background on secondary display:
screenid = max(Screen('Screens'));
[win, winrect] = Screen('OpenWindow', screenid, 0);
Screen('TextSize', win, 24);
HideCursor;
% Make luminance only texture:
lumatex = Screen('MakeTexture', win, luma);
% Compute destination rectangle for a 0.5 scaling:
rect = Screen('Rect', lumatex);
s1 = RectWidth(rect) / RectWidth(winrect);
s2 = RectHeight(rect) / RectHeight(winrect);
sf = min(1/s1, 1/s2) * 0.5;
rect = ScaleRect(rect, sf, sf);
dstRect = CenterRect(rect, winrect);
% "Rotate" hue values by 0.5 or 180 degrees for "anti-colors":
hsv(:,:,1) = mod(hsv(:,:,1) + 0.5, 1);
% MK: Modifying saturation not very effective. Leave untouched. hsv(:,:,2) = 1.0;
% Fix luminance to 50% peak - No luminance info in anti-color image:
hsv(:,:,3) = 0.5;
% Convert back from HSV to RGB space:
anticolors = hsv2rgb(hsv) * 255;
% Make a texture out of it:
antitex = Screen('MakeTexture', win, anticolors);
while 1
% Display anti-color image, with a superimposed fixation cross:
Screen('DrawTexture', win, antitex, [], dstRect);
DrawFormattedText(win, '+', 'center', 'center', 0);
Screen('Flip', win);
% Wait for keystroke:
[secs, keycode] = KbStrokeWait;
if keycode(left)
% Left arrow: Draw neutral white:
Screen('FillRect', win, 255, dstRect);
else
% Other key: Draw luminance-only image:
Screen('DrawTexture', win, lumatex, [], dstRect);
DrawFormattedText(win, '+', 'center', 'center', 0);
end
Screen('Flip', win);
% Wait for keystroke:
[secs, keycode] = KbStrokeWait;
% Escape exits:
if keycode(escape)
break;
end
end
% Done. Close window and release all ressources:
ShowCursor;
sca;
return;
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