How can I correct my code which is related to digital image processing?

Question

My aim is to obtain the given photo which includes black color for left upper part and white color right bottom part. In the photo, it is clearly seen that black color(0) is going to be white color(255) by going diagonally and also both x and y coordinates. It is done in matlab by doing digital image processing but I'm not able get it as 100%. 1)You supposed to a photo as grayscaled photo( in the code grayImage2). Then, you need to apply your procedure in order to get the result which I mentioned above for getting the photo. 2)Also, my grayscaled image size is 400x400. Could you help me to correct the code? Thanks in advance.

[x,y,z]= size(grayImage2);

centerX2 = y;

centerY2 = x;

radius2 = 0;  % Change this value to set the desired radius

% Calculate the maximum radius from the center to the corners

maxRadius = sqrt((centerX2 - 1)^2 + (centerY2 - 1)^2);

% Iterate through the diagonal and change pixel values to gray tones

% Iterate through all pixels

for i = 1:x
     for j = 1:y
        if(j>=256)% because of being 400 for one edge for size 
          % Calculate the distance from the center to the current pixel  
          distance2 = sqrt((j - centerX2)^2 + (i - centerY2)^2);
          % Calculate the gray value based on the distance
          grayValue = uint8((distance2 / maxRadius) * (255-(400-j)));
          % Set the pixel to the calculated gray value
          grayImage2(i, j) = grayValue;
        else
          % Calculate the distance from the center to the current pixel
          distance2 = sqrt((j - centerX2)^2 + (i - centerY2)^2);
          % Calculate the gray value based on the distance
          grayValue = uint8((distance2 / maxRadius) * (255-(255-j+1)));
          % Set the pixel to the calculated gray value
          grayImage2(i, j) = grayValue;
        end
   end
end

figure;

% Display the grayscale image

imshow(grayImage2);

title('Grayscale Image with Radial Gradient');

Answer 1

Looks like you're kind of on the right track but it looks a bit complicated. How about something like this?

image = uint8(zeros(400)); 
width = size(image,1); 
height = size(image,2); 
maxR = sqrt(width^2 + height^2); 
for i = 1:width
    for j = 1:height
        r = sqrt(i^2 + j^2);
        image(i,j) = uint8(floor(255*r/maxR));
    end 
end 
imshow(image)