I have a simple little Qt/MySql program that puts a JPG image in a MySQL database and then retrieves it. It looks like it "works", but when I save out the image that I retrieve, the size of the two files (the one I read from disk originally and the one I save out) are different sizes (original is ~69Kb and the saved outr is ~14Kb). Now I can't tell any difference in the images in an image viewer but I cant tell why the sizes are different. But if I do this method for a .bmp file the sizes are the same. Anyone have an explanation?

The database only has 2 columns
id - integer
image - mediumblob

Here is the code:

Qt Code: 
  1. QVariant id(0);
  2.    QByteArray bytes;
  3.    QBuffer buffer(&bytes);
  4.    QImage  testImage;
  5.    QImageWriter writer(&buffer, "JPG");
  6.  
  7.    bool test = testImage.load("testOut.jpg","JPG");
  8.    int numBytes = testImage.numBytes();
  9.    writer.write(testImage);
  10.    QByteArray data = buffer.data();
  11.  
  12.    //Put image in database as byteArray
  13.    if(!query->prepare("INSERT into testBlob (id,image) VALUES (?,?)"))
  14.       qDebug() << query->lastError().text();
  15.  
  16.    query->addBindValue(id);
  17.    query->addBindValue(data);
  18.  
  19.    if(!query->exec())
  20.    {
  21.       qDebug() << query->lastError().text();
  22.    }
  23.  
  24.    //Now get image back out of database
  25.    if(!query->prepare("SELECT * FROM testBlob where id = 11 "))
  26.       qDebug() << query->lastError().text();
  27.  
  28.    if(!query->exec())
  29.    {
  30.       qDebug() << query->lastError().text();
  31.    }
  32.  
  33.    QByteArray image;
  34.    if(query->first() == true)
  35.    {
  36.       QSqlRecord rec = query->record();
  37.       int id = query->value(rec.indexOf("id")).toInt();
  38.       image = query->value(rec.indexOf("image")).toByteArray();
  39.    }
  40.  
  41.    //Write retrieved image out to disk to compare to original
  42.    QImage  imageWrite;
  43.    imageWrite.loadFromData(image,"JPG");
  44.    imageWrite.save("savedImage.jpg","JPG");
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