QImage and Memoey Mapped Files

[Leviathan]

Hi. I want bind QImage to the MMF file to manipulate the image without the cost of memory directly on the disc. Unfortunately, my code creates a copy in memory.

QFile file("Boston City Flow.jpg");
  if(!file.open(QIODevice::ReadOnly))
    QMessageBox::information(this, "Error", "Error");
 
  qint64 size = file.size();
  unsigned char *mmf = file.map(0, size);
 
  QImage image;
  image.loadFromData(mmf, size, NULL);

QFile file("Boston City Flow.jpg");
  if(!file.open(QIODevice::ReadOnly))
    QMessageBox::information(this, "Error", "Error");

  qint64 size = file.size();
  unsigned char *mmf = file.map(0, size);

  QImage image;
  image.loadFromData(mmf, size, NULL);

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My program needs to handle very large images.

[tbscope]

Use streams and read/write in smaller packages.

[Leviathan]

how? can you give an example for jpeg?

[wysota]

JPEG requires all data to be loaded to be able to manipulate it. mmapping a jpeg would do you no good as the data has to be decompressed and reassembled before it actually becomes an image. You could mmap a BMP file and even maybe an uncompressed PNG file but surely not a JPEG file, regardless if you're using Qt or not.