Reading big images in Qt
Article Metadata
Tested with
SDK: Qt "Tower" pre-release
Devices(s): Nokia 5800 XpressMusic, Nokia N97, Nokia N900
Compatibility
Platform(s): Qt
Article
Keywords: QImageReader
Created: tepaa
(24 Nov 2009)
Last edited: hamishwillee
(11 Oct 2012)
Contents |
Overview
This example shows you how to load big images into memory using QImageReader.
Successive loading of big images with a large memory footprint using the QPixmap::load() method may sometimes fail due to RAM restrictions (detected with images taken with the device camera on Nokia 5800 XpressMusic or Nokia N97). To avoid this, you have to use QImageReader and set QImageReader::setScaledSize() for the reader before loading the image. The following code has been tested with JPEG images.
Preconditions
None
Source
QImageReader reader;
// Set image name
reader.setFileName("mypicture.jpg");
// Read image current size
QSize imageSize = reader.size();
// Scale image to fit to screen
imageSize.scale(size(), Qt::KeepAspectRatio);
// Set wanted image size for reader
reader.setScaledSize(imageSize);
// Read image
QImage image = reader.read();
// Make QPixmap (if needed)
QPixmap pixmap = QPixmap::fromImage(image);
Postconditions
The device is able to read big JPEG images.
Oleg chuta -
It doesn't work for large .png file (21kx21k), scaling is done to 400x400, but QImage() returns null. Have any other ideas?oleg_chuta 10:25, 27 February 2013 (EET)