Increase contrast from a gray window to the max contrast of the grating

Programming Help
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1

Hello! I’m using Matlab_R2020a on a macOS. I’d like to know how to increase the contrast from a gray window to the max contrast of the Gabori. Thank you so much!!
I have already read all the tutorial, could you please text the code?
(every dt of the stimulus duration, the contrast increase)

%% Define colors
black = 0;
white = 255 ;
gray = (white+1)/2;

%% Open a window
[window, windowRect] = Screen('OpenWindow', screenNumber, gray);

%% Get the size and the center coordinate of the window
[screenXpixels, screenYpixels] = Screen('WindowSize', window);
[xCenter, yCenter] = RectCenter(windowRect);
[width, height] = Screen('DisplaySize', screenNumber); % udm: mm

%% Set-up alpha blending
Screen('BlendFunction', window, GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

dim =12;

%% Grating setup
widthOfGrid = 400;
widthArray = (-widthOfGrid) : widthOfGrid; % widthArray is used in creating the meshgrid
[x, y] = meshgrid(widthArray, widthArray);

%% Grating Frequency
fs_min = 1;
fs_max = 12; 
N_fs = 8;
fs_range_cd = logspace(log10(fs_min), log10(fs_max), N_fs);
fs_cp = fs_range_cd .* (1/conv_pix_deg);

%% Grating Contrast
if gray==white
gray=black;
end
absoluteDifferenceBetweenWhiteAndGray = abs(white - gray);

min_contrast = 0.1;
max_contrast = 0.8;
N_contr = 6;
contrast_range = logspace(log10(min_contrast), log10(max_contrast), N_contr);

absoluteDifferenceBetweenMaxAndGray = (contrast_range .* gray);

%% Frequency and Contrast Combination
M = N_fsN_contr;
m = 6;
nTrials = Mm;
t = randperm(nTrials);

FreqContr = zeros(M,2);
FreqContr_tot = zeros(nTrials,2);
c = 0;
f = 0;

for a = 1:N_fs
    for b = 1:N_contr
        c = c + 1;
        FreqContr(c,:)=[fs_cp(a) absoluteDifferenceBetweenMaxAndGray(b)];
    end
end

for d = 1:m
    for e = 1:M
        f = f + 1;
        FreqContr_tot(f,:) = FreqContr(e,:);
    end
end

rand_FreqContr = FreqContr_tot(t,:);

%% Set structure
p.contrasts = absoluteDifferenceBetweenMaxAndGray;
p.SFs = fs_range_cd;
p.repeats = m;

stim_secs = 10;

%% Time start
timeStart_exp = GetSecs;

for k=1:dim
g = g + 1;
%cosd & sind (cos & sin in degrees)
A = cosd(alpha_angle) * rand_FreqContr(g,1);
B = sind(alpha_angle) * rand_FreqContr(g,1);

        gratingMatrix = sin(A*x+B*y); %Converts meshgrid into a sinusoidal grating

        % Gaussian function
        circularGaussianMaskMatrix = exp(-((x .^ 2) + (y .^ 2)) / (sigma ^ 2));   
        
        % Since each entry of gratingMatrix varies between minus one and one and each entry of
        % circularGaussianMaskMatrix vary between zero and one, each entry of
        % imageMatrix varies between minus one and one.
        % -1 <= imageMatrix(x0, y0) <= 1
        imageMatrix = gratingMatrix .* circularGaussianMaskMatrix;          
        
        % Since each entry of imageMatrix is a fraction between minus one and one, 
        % multiplying imageMatrix by absoluteDifferenceBetweenWhiteAndGray and adding 
        % the gray color code baseline converts each entry of imageMatrix into a shade of gray:          
        grayscaleImageMatrix = gray + absoluteDifferenceBetweenWhiteAndGray * imageMatrix; 
        

        centeredRect = CenterRectOnPointd(baseRect, rand_C(k,1), rand_C(k,2)); 
        Screen('PutImage', window, grayscaleImageMatrix, centeredRect);


      Screen('Flip', window);
        
      timeStart_stim = GetSecs;
      timeEnd_stim = timeStart_stim + stim_secs;
      T_stim = GetSecs;
        
      trial = trial + 1;

end