Hello. I need to transform a folder of PNG gray pictures to hex files

I have a folder that has hundreds of PNG gray images that I need automate their transformation into hex files for classification

[Rik]

What you mean by hex file? Do you mean you want to store the image as a long list of binary values? Or should it be a text file with each value represented as hexadecimal strings?

And once you have written the code for one, you can simply loop to do the rest.

[Ziad Osman]

I mean a text file with each pixel in the PNG picture represented as hexadecimal string and do this for all pictures

[dpb]

"... a text file with each pixel in the PNG picture represented as hexadecimal string"

Let me ask "Why?". What can you do/are you going to do with the string representation you can't do directly from the binary representation already have which is same numerically as will be the result of reading the hex number?

[DGM]

You will have no indication of the geometry or depth of the image. You'll just have a vector of values. Vectorized in what direction? Who knows. That was never specified.

How do you propose to store geometry information? Does it matter which way the data is vectorized? If we don't need to devectorize the data for analysis, maybe we don't need those details, but we don't know that.

If you have a reason to be cramming image data into text files, then surely you're doing so because you're trying to adhere to some existing convention for doing so. It seems you're pursuing this format because you already have something that reads it, but we don't know how to make the format adhere to those expectations unless you say what it is. Otherwise, I don't see why the need exists.

If you want a standardized, simple, easily decodable image format, you can just use PGM/PPM and be done with it. A PGM file consists of the filetype magic number, the geometry, the max grayvalue, followed by the uncompressed pixel data vectorized row-wise. It can be encoded in plain text or binary, and imwrite() can write either.

Answer 1

[Walter Roberson]

projectdir = './inputimages';   %directory to look for png files
hexfiledir = './hexdir';        %directory to store hex files
hexext = '.txt';
if ~isdir(hexfiledir); mkdir(hexfiledir); end

dinfo = dir( fullfile(projectdir, '*.png'));
filenames = fullfile( {dinfo.folder}, {dinfo.name});
numfiles = numel(filenames);
for K = 1 : numfiles
    thisfile = filenames{K};
    [~, basename, ~] = fileparts(thisfile);
    outfile = fullfile( hexfiledir, [basename hexext]);
    img = fileread(thisfile);
    hexdata = reshape( dec2hex(img(:), 2).', 1, []);
    [fid, msg] = fopen(outfile, 'w');
    if fid < 0; error('failed to open file "%s" for writing because "%s"', outfile, msg); end
    fwrite(fid, hexdata);
    fclose(fid);
end

This will read .png files that live within projectdir, and convert the image content into row vectors of hex data, following down columns. If the png happen to be color images, the red pixel components will appear, then the green pixel components, then the blue pixel components. The hex data is written to .txt files within the hexfiledir