Putting and getting images from MySQL database?

[allensr]

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:

QVariant id(0);
   QByteArray bytes;
   QBuffer buffer(&bytes);
   QImage  testImage;
   QImageWriter writer(&buffer, "JPG");
 
   bool test = testImage.load("testOut.jpg","JPG");
   int numBytes = testImage.numBytes();
   writer.write(testImage);
   QByteArray data = buffer.data();
 
   //Put image in database as byteArray
   if(!query->prepare("INSERT into testBlob (id,image) VALUES (?,?)"))
      qDebug() << query->lastError().text();
 
   query->addBindValue(id);
   query->addBindValue(data);
 
   if(!query->exec())
   {
      qDebug() << query->lastError().text();
   }
 
   //Now get image back out of database
   if(!query->prepare("SELECT * FROM testBlob where id = 11 "))
      qDebug() << query->lastError().text();
 
   if(!query->exec())
   {
      qDebug() << query->lastError().text();
   }
 
   QByteArray image;
   if(query->first() == true)
   {
      QSqlRecord rec = query->record();
      int id = query->value(rec.indexOf("id")).toInt();
      image = query->value(rec.indexOf("image")).toByteArray();
   }
 
   //Write retrieved image out to disk to compare to original
   QImage  imageWrite;
   imageWrite.loadFromData(image,"JPG");
   imageWrite.save("savedImage.jpg","JPG");

QVariant id(0);
   QByteArray bytes;
   QBuffer buffer(&bytes);
   QImage  testImage;
   QImageWriter writer(&buffer, "JPG");

   bool test = testImage.load("testOut.jpg","JPG");
   int numBytes = testImage.numBytes();
   writer.write(testImage);
   QByteArray data = buffer.data();
   
   //Put image in database as byteArray
   if(!query->prepare("INSERT into testBlob (id,image) VALUES (?,?)"))
      qDebug() << query->lastError().text();

   query->addBindValue(id);
   query->addBindValue(data);

   if(!query->exec())
   {
      qDebug() << query->lastError().text();
   }

   //Now get image back out of database
   if(!query->prepare("SELECT * FROM testBlob where id = 11 "))
      qDebug() << query->lastError().text();

   if(!query->exec())
   {
      qDebug() << query->lastError().text();
   }

   QByteArray image;
   if(query->first() == true)
   {
      QSqlRecord rec = query->record();
      int id = query->value(rec.indexOf("id")).toInt();
      image = query->value(rec.indexOf("image")).toByteArray();
   }

   //Write retrieved image out to disk to compare to original
   QImage  imageWrite;
   imageWrite.loadFromData(image,"JPG");
   imageWrite.save("savedImage.jpg","JPG");

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[jcr]

What about the compression-levelof the jpeg that can be set for QImage.save() as the quality parameter?

[patrik08]

I write zip && jpg to db mysql... longblob fields max 2GB
https://qt-webdav.svn.sourceforge.ne...zip/README.txt

whitout
imageWrite.loadFromData(image,"JPG"); QImage
and image stay exact the same as on disc!

important is zip or gunzip to faster write an read on dbs...


and i not lost data from jpg exif or other ...

link http://en.wikipedia.org/wiki/Exif