Unable to convert grayscale images into rgb from a folder.

Hi,

I want to convert grayscale images from a folder into rgb. I would then save the resulting rgb images into a separate folder. Below are my code:

files_loc = 'D:\regionGrowing_MLT\png_orig_imgs1\Training\Benign';
filenames  = dir(fullfile(files_loc,'*.png'));

fnames = {filenames.name};
img_name = fnames{1};
img_file = fullfile(files_loc,img_name);

save_dir = 'D:\regionGrowing_MLT\png_orig_imgs1\Training\Benign\trainColorBenign';
for iter = 1:length(fnames)
    img_name = fnames{iter};
    png_name =strsplit(img_name,'.');
    png_name = png_name{1}
    
    new_png_path = fullfile(save_dir,sprintf('%s.png',png_name));
    img_file = fullfile(files_loc,img_name);
    rgbImage = cat(3, img_file, img_file, img_file);
    imwrite(rgbImage(iter),new_png_path,'mode','loseless');
end

However, I get the following error message:

Error using imwrite>parse_inputs (line 615)

First argument must be image data specified by a numeric matrix.

Error in imwrite (line 440)

[data, map, filename, format, paramPairs] = parse_inputs(varargin{:});

Error in colorconv (line 17)

imwrite(rgbImage(iter),new_png_path,'mode','loseless');

Answer 1

[DGM]

imwrite() needs numeric/logical data as its primary input. You're feeding it a 3D char array of file paths. Read the file, concatenate, write. The fix might be something like the following, though I didn't set up a sandbox to test this.

% ...
imgdata = imread(img_file);
rgbImage = repmat(imgdata,[1 1 3]);
imwrite(rgbImage,new_png_path,'mode','loseless');
% ...

There might be other ways to do this quicker, but something like this should work.

[Warid Islam]

Hi @DGM,

It worked perfectly. Thank you.