How can I get the matrix of the grayscale image?

The code that I've written is as follows:

    i = imread('Image_Name.bmp');

    imshow(i);

    input = i; % To store values of 'i' in 'input'

    inmin = min(i); % To store values of 'min(i)' in 'inmin'.

    inmax = max(i); % To store values of 'max(i)' in 'inmax'.

All of the above is in Command Window.

And the following is in Workspace Window.

i = 500x500x3 unit8

inmax = 1x500x3 unit8

inmin = 1x500x3 unit8

input = 500x500x3 unit8

j = 1

k = 500

zeros 1x500double

In the Editor Window.

    k = 500;

    zeros = (1:500);

    for b = 1:k

      for j = 1:k

         disp (input(k,k)-inmin(b,j)) % I've taken 'input(k,k)' as its dimension is 500x500x3

      end

   end

It gives me some values and then showcases the error "Index exceeds matrix dimensions. Error in disp (input(k,k)-inmin(b,j))" Please help me. I'm new to MATLAB so I'm having difficulty with it.

[Florian Morsch]

Could you try k=499 instead of 500 and see if you get a error again?

[Rhea S Shrivastava]

I'm getting the same error again.

Answer 1

[KSSV]

You should use the following to get the min and max:

inmin = min(i,[],3); % To store values of 'min(i)' in 'inmin'.
inmax = max(i,[],3); % To store values of 'max(i)' in 'inmax'.

[Rhea S Shrivastava]

I've got the 'inmin' and 'inmax'. Now, when I subtracted these two arrays, all I got was zeros(Command Window).

How can I implement '((input - inmin)/(inmax - inmin))*255' through for loop, where 'input', 'inmin' and 'inmax' are the pixel values?

[KSSV]

YOu need not to use loop for that..you can straight away use:

((input - inmin)./(inmax - inmin))*255

[Rhea S Shrivastava]

When I do it that way, all i get is the array of zeros. I need to apply this formula on each pixel. Hence, I need to use the for loop, but I'm stuck with its initialization.

[Image Analyst]

You need to cast to single or double. If you subtract a value from a uint8 or uint16 image and the result is less than 0, all you will see is zero. And don't use input as the name of your variable since it's the name of a built-in function.

Answer 2

[Image Analyst]

Lots wrong with that code. Just try this:

rgbImage = imread('peppers.png');
[rows, columns, numberOfColorChannels] = size(rgbImage)
imshow(rgbImage);
drawnow;

% Extract the individual red, green, and blue color channels.
redChannel = double(rgbImage(:, :, 1));
greenChannel = double(rgbImage(:, :, 2));
blueChannel = double(rgbImage(:, :, 3));

minR = min(redChannel(:))
minG = min(greenChannel(:))
minB = min(blueChannel(:))
maxR = max(redChannel(:))
maxG = max(greenChannel(:))
maxB = max(blueChannel(:))
for col = 1 : columns
  for row = 1 : rows
    message = sprintf('For row=%d, col=%d, diff = %.1f in the red, %.1f in the green, and %.1f in the blue',...
      row, col,...
      redChannel(row, col) - minR, ...
      greenChannel(row, col) - minG, ...
      blueChannel(row, col) - minB);
    fprintf('%s\n', message);
  end  
end