Conversion of .BMP to .jpg images

Im using the code below to convert .bmp images to .jpeg, Once typed into the command window no errors appear. However there are no new images written into the 'JPEG Data' folder, Can anyone help?

    %load images from file
    filePathIn = '.\Project\Matlab Folder\BMP Data';
    filePathOut = '.\Project\Matlab Folder\JPEG Data';

    %Load names of .bmp files in folder filePathIn
    d = dir([filePathIn,'*.bmp']);

    %for each .bmp file in the directory, convert to jpg
    for i = 1:length(d)   

        %read .bmp file
        fname = d(i).name;
        %BMP = imread([filePathIn,d(i).name]); 
        BMP = imread([filePathIn,fname]);

        %convert to jpg and rename with .jpg extension
        fname = [fname(1:end-4),'.jpg'];
        imwrite(BMP,[filePathIn,fname],'jpg');   

        %reload this file in .jpg format
        A = imread([filePathIn,fname]);
        rgbImage = repmat(A,[1 1 3]);

        %write jpg image to new folder
        imwrite(rgbImage,[filePathOut,fname],'JPEG','Quality',100);

    end

Answer 1

[Image Analyst]

Sean, try this code:

% Demo to create JPG copies of BMP files in a different folder.
% By Image Analyst
% inputFolder = fileparts(which('cameraman.tif')) % Determine where demo folder is (works with all versions).
inputFolder = fullfile(pwd, 'Project\Matlab Folder\BMP Data');
filePattern = fullfile(inputFolder, '*.bmp')
% Get list of all BMP files in input folder
bmpFiles = dir(filePattern)
% Create the output folder:
outputFolder = fullfile(pwd, 'Project\Matlab Folder\JPEG Data')
if ~exist(outputFolder, 'dir')
  mkdir(outputFolder);
end
figure;
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% Loop over all bmp files, making a jpg version 
% of them in the output folder.
for k = 1 : length(bmpFiles)
  % Read in .bmp file
  baseFileName = bmpFiles(k).name;
  fullFileNameInput = fullfile(inputFolder, baseFileName)
  rgbImage = imread(fullFileNameInput);
  subplot(1, 2, 1);
  imshow(rgbImage);
  title('Original image', 'FontSize', 30);
  drawnow;
  
  % Prepare output file name
  fullFileNameOutput = fullfile(outputFolder, baseFileName);
  % Converts to JPEG and gives it the .jpg extension
  fullFileNameOutput = strrep(lower(fullFileNameOutput), '.bmp', 'jpg')
  imwrite(rgbImage,fullFileNameOutput);

  % Reloads it in a JPEG format to see how bad the compression artifacts are.
  rgbImage = imread(fullFileNameOutput);
  subplot(1, 2, 2);
  imshow(rgbImage);
  title('Recalled JPG image', 'FontSize', 30);
  drawnow;
  pause(1);
end
% Open Windows Explorer to the output folder:
winopen(outputFolder);

[Sean]

great got it working, really good notation aswell, very good to follow. thanks for the help, really appreciate it.

Answer 2

[matt dash]

Looks like you're missing a path separator between your folder name and file name. You should use the fullfile fucntion to combine paths with filenames instead of trying to do it with [].

[Sean]

Is it not wrong to use brackets inside of brackets? for example for the code below if I where to use the fullfile function I would be using '()' inside '()'

imwrite(rgbImage,[filePathOut,fname],'JPEG','Quality',100);

[Sean]

I've used the code below with the fullfile function but the same problem is still occurring

for i = 1:length(d)   

    %read .bmp file
    fname = d(i).name;
    %BMP = imread([filePathIn,d(i).name]); 
    BMP = imread(fullfile(filePathIn,fname));

    %convert to jpg and rename with .jpg extension
    fname = [fname(1:end-4),'.jpg'];
    imwrite(BMP,fullfile(filePathIn,fname),'jpg');   

    %reload this file in .jpg format
    A = imread(fullfile(filePathIn,fname));
    rgbImage = repmat(A,[1 1 3]);

    %write jpg image to new folder
    %imwrite(rgbImage,[filePathOut,fname],'jpg');
    imwrite(rgbImage,fullfile(filePathOut,fname),'JPEG','Quality',100);
end

[Eric]

Can you use copyfile to generate the second image rather than writing it out a second time? This seems more efficient. More importantly, if this fails then the problem is not in how you're calling imwrite and so on, but perhaps is an indication of access problems.

[Image Analyst]

No you can't. Copying a file and giving it a new extension only changes the filename, not the data in the file. You have to call imread(), then imwrite() with a new filename. You do not need to call them twice like the code above is showing.

[Sean]

I got it working with the code below, although the new images are re written in the same directory. Therefore the problem lay with writing images in a new folder.

%Creates structure  of bitmap images inside working directory
  d=dir('*.bmp');
  for i=1:length(d)
      %Reads in .bmp file
      fname=d(i).name;
      BMP=imread(fname);
      %Converts to JPEG and gives it the .jpg extension
      fname = [fname(1:end-4),'.jpg'];
      imwrite(BMP,fname,'jpg');
      %Reloads it in a JPEG format
      A = imread(fname);
      rgbImage = repmat(A,[1 1 3]);
      %Rewrites in into working Directory
      imwrite(rgbImage,fname,'JPEG','Quality',100);
  end

[Eric]

That's what I was getting at in my comment above. I didn't mean copy the BMP file and simply rename it to JPG, but to copy the first jpeg (the one that wrote correctly) to the location where the write failed.

You could check two things:

1. Does the output directory exist when you try to write to it?

2. Do you have write privileges to the directory?

-Eric