Load and save image - file size drastically reduced



  • Can anybody help me to understand why the following generates a .jpg file of only 353KB from a 2MB source?

    I thought I had found a simple solution with image->load and image->save but the image file size changes on a straight transfer?
    'temp_file’ is the input file and ‘current_file’ is the result. (Obviously there are a number of other variables too.)
    Any help would be apreciated.

    @ // Make directories if they don't exist
    QDir mdir;
    QString mdpath = path + project + "/" + camNo + "/" + yearMonth;
    if(!mdir.exists(mdpath))
    {
    mdir.mkpath(mdpath);
    qDebug() << “Directory Created";
    }
    else
    {
    qDebug() << “Directory Already Exists";
    }

    // Save the image
    QString mfpath = path + project + "/" + camNo + "/" + yearMonth + "/" + current_file;
    QImage *image = new QImage();
    if(!mdir.exists(mfpath))
        {
            if(image->load(temp_file))
                {
                image->save(mfpath);
                }
            qDebug() << "Image Project = "+project+" Image Saved";
        }
        else
        {
            qDebug() << "Image Project = "+project+" Image Already Exists";
        }@

  • Moderators

    JPG is a lossy format: it will always change size (and loose quality!) when you save it again. If you want to preserve the file data, use QFile::copy() instead. It will also be much faster.


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