Creating Patches for all images in a directory

I have a program that takes an image and create patches (28*28) from that image and then saves each patches as separate images.

fullFileName='demo.jpg';
rgbImage = imread(fullFileName);
imshow(rgbImage);

set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
drawnow;

[rows columns numberOfColorBands] = size(rgbImage)

blockSizeR = 28; % Rows in block.
blockSizeC = 28; % Columns in block.

wholeBlockRows = floor(rows / blockSizeR);
blockVectorR = [blockSizeR * ones(1, wholeBlockRows)];

wholeBlockCols = floor(columns / blockSizeC);
blockVectorC = [blockSizeC * ones(1, wholeBlockCols)];

if numberOfColorBands > 1
    
    ca = mat2cell(rgbImage, blockVectorR, blockVectorC, numberOfColorBands);
else
    ca = mat2cell(rgbImage, blockVectorR, blockVectorC);
end


plotIndex = 1;
numPlotsR = size(ca, 1);
numPlotsC = size(ca, 2);
for r = 1 : numPlotsR
    for c = 1 : numPlotsC
        fprintf('plotindex = %d,   c=%d, r=%d\n', plotIndex, c, r);
        subplot(numPlotsR, numPlotsC, plotIndex);
        rgbBlock = ca{r,c};
        newimage=sprintf('demo%03d', plotIndex);
        imshow(rgbBlock); 
        imwrite(rgbBlock, [newimage, '.jpg']);
        
        
        [rowsB columnsB, numberOfColorBandsB] = size(rgbBlock);
        caption = sprintf('Block #%d of %d\n%d rows by %d columns', ...
        plotIndex, numPlotsR*numPlotsC, rowsB, columnsB);
        title(caption);
       
        
        drawnow;
        
        plotIndex = plotIndex + 1;
    end
end

Now I want this program to take all images from a given directory (say, C:/folder/) and create patches for each of the images. For example- If there are 10 images in the directory,then it will create (10*64=640) patches Please help me out on this.

[Stephen23]

Use either of the methods shown here:

https://www.mathworks.com/help/matlab/import_export/process-a-sequence-of-files.html

Answer 1

[Mahesh Taparia]

Hi,

To read the images from a folder, firstly you need to give the path of that folder, then run a loop to read each image, create a patch of required size and save it. You can use ‘dir’ to list the contents of a folder.

You can follow:

Image_folder=dir('PATH TO FOLDER\*.jpg'); 
N = length(Image_folder); 
for i=1:N 
        I=strcat('PATH TO FOLDER\',Image_folder(i).name); 
        rgbImage=imread(I); 
%% 
%%ADD YOUR CODE FOR PATCH EXTRACTION OF 1 IMAGE 
%% 
end 

[Stephen23]

Note that fullfile is preferred for generating filenames, rather than strcat:

I = fullfile('PATH TO FOLDER',Image_folder(i).name);

[Md Farhad Mokter]

Hi Mahesh Taparia.

Thanks for your answer. I have followed the given solution. It seems like the program is working for each images correctly but the patches are replaced for each images. The patches created for the first image is being replaced by the patches created from second image. At the end of program, only patches from the last image remains there.

I am pasting the code for your conveneince.

Image_folder=dir('C:\Users\USER\Desktop\New folder\*.jpg'); 
N = length(Image_folder); 
for i=1:N 
        I=strcat('C:\Users\USER\Desktop\New folder\',Image_folder(i).name); 
        rgbImage=imread(I); 

        
        imshow(rgbImage);

        set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
        drawnow;

        [rows columns numberOfColorBands] = size(rgbImage)

        blockSizeR = 28; % Rows in block.
        blockSizeC = 28; % Columns in block.

        wholeBlockRows = floor(rows / blockSizeR);
        blockVectorR = [blockSizeR * ones(1, wholeBlockRows)];

        wholeBlockCols = floor(columns / blockSizeC);
        blockVectorC = [blockSizeC * ones(1, wholeBlockCols)];

        if numberOfColorBands > 1

            ca = mat2cell(rgbImage, blockVectorR, blockVectorC, numberOfColorBands);
        else
            ca = mat2cell(rgbImage, blockVectorR, blockVectorC);
        end


        plotIndex = 1;
        numPlotsR = size(ca, 1);
        numPlotsC = size(ca, 2);
        for r = 1 : numPlotsR
            for c = 1 : numPlotsC
                fprintf('plotindex = %d,   c=%d, r=%d\n', plotIndex, c, r);
                subplot(numPlotsR, numPlotsC, plotIndex);
                rgbBlock = ca{r,c};
                newimage=sprintf('patch%03d', plotIndex);
                imshow(rgbBlock); 
                imwrite(rgbBlock, [newimage, '.bmp']);


                [rowsB columnsB, numberOfColorBandsB] = size(rgbBlock);
                caption = sprintf('Block #%d of %d\n%d rows by %d columns', ...
                plotIndex, numPlotsR*numPlotsC, rowsB, columnsB);
                title(caption);


                drawnow;

                plotIndex = plotIndex + 1;
            end
        end

        
end 

[Mahesh Taparia]

Hi,

You should use 'i' instead of plotIndex, because each time plotIndex value is set to 1 when new image is loaded. Follow the code below:

Image_folder=dir('C:\Users\USER\Desktop\New folder\*.jpg'); 
N = length(Image_folder); 
for i=1:N 
        I=strcat('C:\Users\USER\Desktop\New folder\',Image_folder(i).name); 
        rgbImage=imread(I); 
        
        imshow(rgbImage);
        set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
        drawnow;
        [rows columns numberOfColorBands] = size(rgbImage)
        blockSizeR = 28; % Rows in block.
        blockSizeC = 28; % Columns in block.
        wholeBlockRows = floor(rows / blockSizeR);
        blockVectorR = [blockSizeR * ones(1, wholeBlockRows)];
        wholeBlockCols = floor(columns / blockSizeC);
        blockVectorC = [blockSizeC * ones(1, wholeBlockCols)];
        if numberOfColorBands > 1
            ca = mat2cell(rgbImage, blockVectorR, blockVectorC, numberOfColorBands);
        else
            ca = mat2cell(rgbImage, blockVectorR, blockVectorC);
        end
       
        numPlotsR = size(ca, 1);
        numPlotsC = size(ca, 2);
        for r = 1 : numPlotsR
            for c = 1 : numPlotsC
                fprintf('plotindex = %d,   c=%d, r=%d\n', i, c, r);
                subplot(numPlotsR, numPlotsC, plotIndex);
                rgbBlock = ca{r,c};
                newimage=sprintf('patch%03d', plotIndex);
                imshow(rgbBlock); 
                imwrite(rgbBlock, [newimage, '.bmp']);
                [rowsB columnsB, numberOfColorBandsB] = size(rgbBlock);
                caption = sprintf('Block #%d of %d\n%d rows by %d columns', ...
                plotIndex, numPlotsR*numPlotsC, rowsB, columnsB);
                title(caption);
                drawnow;
               
            end
        end
        
end 

[Stephen23]

@Mahesh Taparia: your code produces quite a few warnings in the MATLAB editor, which should be fixed. See also:

https://www.mathworks.com/matlabcentral/answers/35676-why-not-use-square-brackets

Note that fullfile is preferred over string concatenation.

[Guillaume]

In addition, the floor in the block count calculations are pointless. If floor does have to do some rounding because the image size is not a multiple of the block size, then the mat2cell call will fail. Ideally, an assert should be added or the calcuation of the block vectors should be improved to add the leftover pixels.

Also, the if is also pointless. When numberOfColorBands is 1, the two mat2cell calls do exactly the same.

I know both of these were in the original code, but there's no reason not to improve it.