Reading and Writing Image Files#
The most common way to read images is through
QPixmap ‘s constructors, or by calling the QImage::load() and
load() functions. In addition, Qt provides the
QImageReader class which gives more control over the process. Depending on the underlying support in the image format, the functions provided by the class can save memory and speed up loading of images.
Likewise, Qt provides the
QImageWriter class which supports setting format specific options, such as the gamma level, compression level and quality, prior to storing the image. If you do not need such options, you can use QImage::save() or
QMovieis a convenience class for displaying animations, using the
QImageReaderclass internally. Once created, the
QMovieclass provides various functions for both running and controlling the given animation.
QImageWriter classes rely on the
QImageIOHandler class which is the common image I/O interface for all image formats in Qt.
QImageIOHandler objects are used internally by
QImageWriter to add support for different image formats to Qt.
A list of the supported file formats are available through the
supportedImageFormats() functions. Qt supports several file formats by default, and in addition new formats can be added as plugins. The currently supported formats are listed in the
QImageWriter class documentation.
Qt’s plugin mechanism can also be used to write a custom image format handler. This is done by deriving from the
QImageIOHandler class, and creating a
QImageIOPlugin object which is a factory for creating
QImageIOHandler objects. When the plugin is installed,
QImageWriter will automatically load the plugin and start using it.