image grayscale and distortion

function converted = convertImage(im, alterationType)
    % Main function to alter the image based on alterationType
    % Parameters:
    %   - im: the input image array
    %   - alterationType: numerical value (1, 2, or 3) indicating the type of alteration
    
    % Display original image
    figure;
    subplot(1, 2, 1);
    imshow(im);
    title('Original Image');
    
    % Call the appropriate helper function based on alterationType
    switch alterationType
        case 1
            % Blurring image alteration
            converted = blurImage(im);
            title('Blurred Image');
        case 2
            % Distorting image alteration
            converted = distortImage(im);
            title('Distorted Image');
        case 3
            % Grayscale image alteration
            converted = grayscaleImage(im);
            title('Grayscale Image');
        otherwise
            % No alteration for unknown alterationType
            converted = im;
            title('No Alteration');
    end
    
    % Display altered image
    subplot(2, 2, 1);
    imshow(converted);
end

function blurred = blurImage(im)
    % Helper function to blur the image
    [rows, cols, ~] = size(im);
    blurred = im;

    for i = 2:rows-1
        for j = 2:cols-1
            % Calculate local mean for each pixel
            localMean = mean(mean(im(i-1:i+1, j-1:j+1, :)));
            blurred(i, j, :) = localMean;
        end
    end
end
function distorted = distortImage(im)
    % Helper function to distort the image
    [rows, cols, channels] = size(im);
    halfwayRows = rows / 2;
    halfwayCols = cols / 2;
    distorted = im;

    if channels == 3
        % For color images
        topRight = im(1:halfwayRows, halfwayCols+1:end, :);
        topLeft = im(1:halfwayRows, 1:halfwayCols, :);
        bottomRight = im(halfwayRows+1:end, halfwayCols+1:end, :);
        bottomLeft = im(halfwayRows+1:end, 1:halfwayCols, :);

        distorted(1:halfwayRows, 1:halfwayCols, :) = bottomRight;
        distorted(1:halfwayRows, halfwayCols+1:end, :) = topLeft;
        distorted(halfwayRows+1:end, 1:halfwayCols, :) = topRight;
        distorted(halfwayRows+1:end, halfwayCols+1:end, :) = bottomLeft;
    else
        % For grayscale images
        topRight = im(1:halfwayRows, halfwayCols+1:end);
        topLeft = im(1:halfwayRows, 1:halfwayCols);
        bottomRight = im(halfwayRows+1:end, halfwayCols+1:end);
        bottomLeft = im(halfwayRows+1:end, 1:halfwayCols);

        % Swap quadrants for grayscale values
        distorted(1:halfwayRows, 1:halfwayCols) = bottomRight;
        distorted(1:halfwayRows, halfwayCols+1:end) = bottomLeft;
        distorted(halfwayRows+1:end, 1:halfwayCols) = topRight;
        distorted(halfwayRows+1:end, halfwayCols+1:end) = topLeft;
    end
end
function grayscale = grayscaleImage(im)
    % Helper function to convert the image to grayscale
    [rows, cols, channels] = size(im);
    grayscale = im;

    for i = 1:rows
        for j = 1:cols
            % Calculate grayscale value using the formula
            grayscale(i, j, :) = 1.25 * mean(im(i, j, :));
        end
    end
    
    % Eliminate the third dimension for color images
    if channels == 3
        grayscale = squeeze(grayscale(:, :, 1));
    end
end 

Alter Grayscale Image: convertImage(im, 2) - Expected to distort the image.

Variable studentResult has an incorrect value.

When calling the required convertImage function with the option for distorting the grayscale image, the output from convertImage was not an image array containing a properly distorted grayscale image.

it fails this one test out of 9

please help

Answer 1

[Voss]

In the distortImage function, notice that the code for color images:

distorted(1:halfwayRows, 1:halfwayCols, :) = bottomRight;
distorted(1:halfwayRows, halfwayCols+1:end, :) = topLeft;        % <-
distorted(halfwayRows+1:end, 1:halfwayCols, :) = topRight;
distorted(halfwayRows+1:end, halfwayCols+1:end, :) = bottomLeft; % <-

has topLeft and bottomLeft swapped relative to the code for grayscale images:

distorted(1:halfwayRows, 1:halfwayCols) = bottomRight;
distorted(1:halfwayRows, halfwayCols+1:end) = bottomLeft;        % <-
distorted(halfwayRows+1:end, 1:halfwayCols) = topRight;
distorted(halfwayRows+1:end, halfwayCols+1:end) = topLeft;       % <-

Since the error references grayscale images, I expect that the color block is OK and the grayscale block needs to be changed accordingly. (This interpretation is consistent with the instructions for this project.)

However, also realize that you don't need the grayscale block at all, because the colon used to index along the third dimension of a color image array works just as well for a grayscale image matrix, so all you really need to do is to remove the grayscale block:

        
function distorted = distortImage(im)
    % Helper function to distort the image
    [rows, cols, channels] = size(im);
    halfwayRows = rows / 2;
    halfwayCols = cols / 2;
    distorted = im;
    % if channels == 3
    %     % For color images
    
    % For ALL images:
        topRight = im(1:halfwayRows, halfwayCols+1:end, :);
        topLeft = im(1:halfwayRows, 1:halfwayCols, :);
        bottomRight = im(halfwayRows+1:end, halfwayCols+1:end, :);
        bottomLeft = im(halfwayRows+1:end, 1:halfwayCols, :);
        
        distorted(1:halfwayRows, 1:halfwayCols, :) = bottomRight;
        distorted(1:halfwayRows, halfwayCols+1:end, :) = topLeft;
        distorted(halfwayRows+1:end, 1:halfwayCols, :) = topRight;
        distorted(halfwayRows+1:end, halfwayCols+1:end, :) = bottomLeft;
        
    % else
    %     % For grayscale images
    %     topRight = im(1:halfwayRows, halfwayCols+1:end);
    %     topLeft = im(1:halfwayRows, 1:halfwayCols);
    %     bottomRight = im(halfwayRows+1:end, halfwayCols+1:end);
    %     bottomLeft = im(halfwayRows+1:end, 1:halfwayCols);
    %     % Swap quadrants for grayscale values
    %     distorted(1:halfwayRows, 1:halfwayCols) = bottomRight;
    %     distorted(1:halfwayRows, halfwayCols+1:end) = bottomLeft;
    %     distorted(halfwayRows+1:end, 1:halfwayCols) = topRight;
    %     distorted(halfwayRows+1:end, halfwayCols+1:end) = topLeft;
    % end
end

[Voss]

The point about indexing along the third dimension is that a 2D matrix has an implicit 3rd dimension (and all higher dimensions too) whose size is 1. So you can treat those other dimensions as if they were really there (because they are, they just have size 1).

Example. Create a 3d array A and a 2d matrix M:

format compact
A = magic(3)+reshape(1:3,1,1,[]) % a 3D array

A = 
A(:,:,1) =
     9     2     7
     4     6     8
     5    10     3
A(:,:,2) =
    10     3     8
     5     7     9
     6    11     4
A(:,:,3) =
    11     4     9
     6     8    10
     7    12     5

M = magic(3)                     % a 2D matrix

M = 3×3

8 1 6 3 5 7 4 9 2

Take the first 2 rows and columns from A, across all slices (i.e., the whole 3rd dimension):

A([1 2],[1 2],:) % 2x2x3 array from A

ans = 
ans(:,:,1) =
     9     2
     4     6
ans(:,:,2) =
    10     3
     5     7
ans(:,:,3) =
    11     4
     6     8

Using the same exact syntax, take the first 2 rows and columns from M, across all slices (i.e., the whole 3rd dimension - M has only 1 slice):

M([1 2],[1 2],:) % 2x2(x1) array from M

ans = 2×2

8 1 3 5

[ronit]

Thankyou so much its done

[Voss]

You're welcome!