The QImageWriter class provides a format independent interface for writing images to files or other devices. More...

#include <qimagewriter.h>

Collaboration diagram for QImageWriter:

Public Types
enum	ImageWriterError { UnknownError , DeviceError , UnsupportedFormatError , InvalidImageError }
	This enum describes errors that can occur when writing images with QImageWriter. More...

Public Member Functions
	QImageWriter ()
	Constructs an empty QImageWriter object.

	QImageWriter (QIODevice *device, const QByteArray &format)
	Constructs a QImageWriter object using the device device and image format format.

	QImageWriter (const QString &fileName, const QByteArray &format=QByteArray())
	Constructs a QImageWriter objects that will write to a file with the name fileName, using the image format format.

	~QImageWriter ()
	Destructs the QImageWriter object.

void	setFormat (const QByteArray &format)
	Sets the format QImageWriter will use when writing images, to format.

QByteArray	format () const
	Returns the format QImageWriter uses for writing images.

void	setDevice (QIODevice *device)
	Sets QImageWriter's device to device.

QIODevice *	device () const
	Returns the device currently assigned to QImageWriter, or \nullptr if no device has been assigned.

void	setFileName (const QString &fileName)
	Sets the file name of QImageWriter to fileName.

QString	fileName () const
	If the currently assigned device is a file, or if setFileName() has been called, this function returns the name of the file QImageWriter writes to.

void	setQuality (int quality)
	Sets the quality setting of the image format to quality.

int	quality () const
	Returns the quality setting of the image format.

void	setCompression (int compression)
	This is an image format specific function that set the compression of an image.

int	compression () const
	Returns the compression of the image.

void	setSubType (const QByteArray &type)

QByteArray	subType () const

QList< QByteArray >	supportedSubTypes () const

void	setOptimizedWrite (bool optimize)

bool	optimizedWrite () const

void	setProgressiveScanWrite (bool progressive)

bool	progressiveScanWrite () const

QImageIOHandler::Transformations	transformation () const

void	setTransformation (QImageIOHandler::Transformations orientation)

void	setText (const QString &key, const QString &text)
	Sets the image text associated with the key key to text.

bool	canWrite () const
	Returns `true` if QImageWriter can write the image; i.e., the image format is supported and the assigned device is open for reading.

bool	write (const QImage &image)
	Writes the image image to the assigned device or file name.

ImageWriterError	error () const
	Returns the type of error that last occurred.

QString	errorString () const
	Returns a human readable description of the last error that occurred.

bool	supportsOption (QImageIOHandler::ImageOption option) const
	Returns `true` if the writer supports option; otherwise returns false.

Static Public Member Functions
static QList< QByteArray >	supportedImageFormats ()
	Returns the list of image formats supported by QImageWriter.

static QList< QByteArray >	supportedMimeTypes ()
	Returns the list of MIME types supported by QImageWriter.

static QList< QByteArray >	imageFormatsForMimeType (const QByteArray &mimeType)

Detailed Description

The QImageWriter class provides a format independent interface for writing images to files or other devices.

\inmodule QtGui \reentrant

QImageWriter supports setting format specific options, such as compression level and quality, prior to storing the image. If you do not need such options, you can use QImage::save() or QPixmap::save() instead.

To store an image, you start by constructing a QImageWriter object. Pass either a file name or a device pointer, and the image format to QImageWriter's constructor. You can then set several options, such as quality (by calling setQuality()). canWrite() returns true if QImageWriter can write the image (i.e., the image format is supported and the device is open for writing). Call write() to write the image to the device.

If any error occurs when writing the image, write() will return false. You can then call error() to find the type of error that occurred, or errorString() to get a human readable description of what went wrong.

Call supportedImageFormats() for a list of formats that QImageWriter can write. QImageWriter supports all built-in image formats, in addition to any image format plugins that support writing.

Note: QImageWriter assumes exclusive control over the file or device that is assigned. Any attempts to modify the assigned file or device during the lifetime of the QImageWriter object will yield undefined results. If immediate access to a resource is desired, the use of a scope is the recommended method.

For example:

QString imagePath(QStringLiteral("path/image.jpeg"));
QImage image(64, 64, QImage::Format_RGB32);
image.fill(Qt::red);
{
    QImageWriter writer(imagePath);
    writer.write(image);
}
 
QFile::rename(imagePath,
              QStringLiteral("path/other_image.jpeg"));

See also: QImageReader, QImageIOHandler, QImageIOPlugin, QColorSpace

Definition at line 20 of file qimagewriter.h.

Member Enumeration Documentation

◆ ImageWriterError

enum QImageWriter::ImageWriterError

This enum describes errors that can occur when writing images with QImageWriter.

\value DeviceError QImageWriter encountered a device error when writing the image data. Consult your device for more details on what went wrong.

\value UnsupportedFormatError Qt does not support the requested image format.

\value InvalidImageError An attempt was made to write an invalid QImage. An example of an invalid image would be a null QImage.

\value UnknownError An unknown error occurred. If you get this value after calling write(), it is most likely caused by a bug in QImageWriter.

Enumerator
UnknownError
DeviceError
UnsupportedFormatError
InvalidImageError

Definition at line 24 of file qimagewriter.h.

Constructor & Destructor Documentation

◆ QImageWriter() [1/3]

QImageWriter::QImageWriter ( )

Constructs an empty QImageWriter object.

Before writing, you must call setFormat() to set an image format, then setDevice() or setFileName().

Definition at line 284 of file qimagewriter.cpp.

◆ QImageWriter() [2/3]

QImageWriter::QImageWriter	(	QIODevice *	device,
		const QByteArray &	format )

explicit

Constructs a QImageWriter object using the device device and image format format.

Definition at line 293 of file qimagewriter.cpp.

◆ QImageWriter() [3/3]

QImageWriter::QImageWriter	(	const QString &	fileName,
		const QByteArray &	format = QByteArray() )

explicit

Constructs a QImageWriter objects that will write to a file with the name fileName, using the image format format.

If format is not provided, QImageWriter will detect the image format by inspecting the extension of fileName.

Definition at line 306 of file qimagewriter.cpp.

◆ ~QImageWriter()

QImageWriter::~QImageWriter ( )

Destructs the QImageWriter object.

Definition at line 315 of file qimagewriter.cpp.

Member Function Documentation

◆ canWrite()

bool QImageWriter::canWrite ( ) const

Returns true if QImageWriter can write the image; i.e., the image format is supported and the assigned device is open for reading.

See also: write(), setDevice(), setFormat()

Definition at line 622 of file qimagewriter.cpp.

◆ compression()

int QImageWriter::compression ( ) const

Returns the compression of the image.

See also: setCompression()

Definition at line 460 of file qimagewriter.cpp.

◆ device()

QIODevice * QImageWriter::device ( ) const

Returns the device currently assigned to QImageWriter, or \nullptr if no device has been assigned.

Definition at line 377 of file qimagewriter.cpp.

◆ error()

QImageWriter::ImageWriterError QImageWriter::error ( ) const

Returns the type of error that last occurred.

See also: ImageWriterError, errorString()

Definition at line 695 of file qimagewriter.cpp.

◆ errorString()

QString QImageWriter::errorString ( ) const

Returns a human readable description of the last error that occurred.

See also: error()

Definition at line 705 of file qimagewriter.cpp.

◆ fileName()

QString QImageWriter::fileName ( ) const

If the currently assigned device is a file, or if setFileName() has been called, this function returns the name of the file QImageWriter writes to.

Otherwise (i.e., if no device has been assigned or the device is not a file), an empty QString is returned.

See also: setFileName(), setDevice()

Definition at line 404 of file qimagewriter.cpp.

◆ format()

QByteArray QImageWriter::format ( ) const

Returns the format QImageWriter uses for writing images.

See also: setFormat()

Definition at line 344 of file qimagewriter.cpp.

◆ imageFormatsForMimeType()

QList< QByteArray > QImageWriter::imageFormatsForMimeType ( const QByteArray & mimeType )

static

Since: 5.12

Returns the list of image formats corresponding to mimeType.

Note that the QGuiApplication instance must be created before this function is called.

See also: supportedImageFormats(), supportedMimeTypes()

Definition at line 790 of file qimagewriter.cpp.

◆ optimizedWrite()

bool QImageWriter::optimizedWrite ( ) const

Since: 5.5

Returns whether optimization has been turned on for writing the image.

See also: setOptimizedWrite()

Definition at line 529 of file qimagewriter.cpp.

◆ progressiveScanWrite()

bool QImageWriter::progressiveScanWrite ( ) const

Since: 5.5

Returns whether the image should be written as a progressive image.

See also: setProgressiveScanWrite()

Definition at line 558 of file qimagewriter.cpp.

◆ quality()

int QImageWriter::quality ( ) const

Returns the quality setting of the image format.

See also: setQuality()

Definition at line 434 of file qimagewriter.cpp.

◆ setCompression()

void QImageWriter::setCompression ( int compression )

This is an image format specific function that set the compression of an image.

For image formats that do not support setting the compression, this value is ignored.

The value range of compression depends on the image format. For example, the "tiff" format supports two values, 0(no compression) and 1(LZW-compression).

See also: compression()

Definition at line 450 of file qimagewriter.cpp.

◆ setDevice()

void QImageWriter::setDevice ( QIODevice * device )

Sets QImageWriter's device to device.

If a device has already been set, the old device is removed from QImageWriter and is otherwise left unchanged.

If the device is not already open, QImageWriter will attempt to open the device in \l QIODeviceBase::WriteOnly mode by calling open(). Note that this does not work for certain devices, such as QProcess, QTcpSocket and QUdpSocket, where more logic is required to open the device.

See also: device(), setFileName()

Definition at line 362 of file qimagewriter.cpp.

◆ setFileName()

void QImageWriter::setFileName ( const QString & fileName )

Sets the file name of QImageWriter to fileName.

Internally, QImageWriter will create a QFile and open it in \l QIODevice::WriteOnly mode, and use this file when writing images.

See also: fileName(), setDevice()

Definition at line 389 of file qimagewriter.cpp.

◆ setFormat()

void QImageWriter::setFormat ( const QByteArray & format )

Sets the format QImageWriter will use when writing images, to format.

format is a case insensitive text string. Example:

QImageWriter writer;

writer.setFormat("png"); // same as writer.setFormat("PNG");

You can call supportedImageFormats() for the full list of formats QImageWriter supports.

See also: format()

Definition at line 334 of file qimagewriter.cpp.

◆ setOptimizedWrite()

void QImageWriter::setOptimizedWrite ( bool optimize )

Since: 5.5

This is an image format-specific function which sets the optimize flags when writing images. For image formats that do not support setting an optimize flag, this value is ignored.

The default is false.

See also: optimizedWrite()

Definition at line 517 of file qimagewriter.cpp.

◆ setProgressiveScanWrite()

void QImageWriter::setProgressiveScanWrite ( bool progressive )

Since: 5.5

This is an image format-specific function which turns on progressive scanning when writing images. For image formats that do not support setting a progressive scan flag, this value is ignored.

The default is false.

See also: progressiveScanWrite()

Definition at line 546 of file qimagewriter.cpp.

◆ setQuality()

void QImageWriter::setQuality ( int quality )

Sets the quality setting of the image format to quality.

Some image formats, in particular lossy ones, entail a tradeoff between a) visual quality of the resulting image, and b) encoding execution time and compression level. This function sets the level of that tradeoff for image formats that support it. For other formats, this value is ignored.

The value range of quality depends on the image format. For example, the "jpeg" format supports a quality range from 0 (low visual quality, high compression) to 100 (high visual quality, low compression).

See also: quality()

Definition at line 424 of file qimagewriter.cpp.

◆ setSubType()

void QImageWriter::setSubType ( const QByteArray & type )

Since: 5.4

This is an image format specific function that sets the subtype of the image to type. Subtype can be used by a handler to determine which format it should use while saving the image.

For example, saving an image in DDS format with A8R8G8R8 subtype:

QImageWriter writer("some/image.dds");
if (writer.supportsOption(QImageIOHandler::SubType))
    writer.setSubType("A8R8G8B8");
writer.write(image);

Definition at line 477 of file qimagewriter.cpp.

◆ setText()

void QImageWriter::setText	(	const QString &	key,
		const QString &	text )

Sets the image text associated with the key key to text.

This is useful for storing copyright information or other information about the image. Example:

QImage image("some/image.jpeg");
QImageWriter writer("images/outimage.png", "png");
writer.setText("Author", "John Smith");
writer.write(image);

If you want to store a single block of data (e.g., a comment), you can pass an empty key, or use a generic key like "Description".

The key and text will be embedded into the image data after calling write().

Support for this option is implemented through QImageIOHandler::Description.

See also: QImage::setText(), QImageReader::text()

Definition at line 609 of file qimagewriter.cpp.

◆ setTransformation()

void QImageWriter::setTransformation ( QImageIOHandler::Transformations transform )

Since: 5.5

Sets the image transformations metadata including orientation to transform.

If transformation metadata is not supported by the image format, the transform is applied before writing.

See also: transformation(), write()

Definition at line 573 of file qimagewriter.cpp.

◆ subType()

QByteArray QImageWriter::subType ( ) const

Since: 5.4

Returns the subtype of the image.

See also: setSubType()

Definition at line 489 of file qimagewriter.cpp.

◆ supportedImageFormats()

QList< QByteArray > QImageWriter::supportedImageFormats ( )

static

Returns the list of image formats supported by QImageWriter.

By default, Qt can write the following formats:

\table \header

Format
MIME type
Description \row
BMP
image/bmp
Windows Bitmap \row
JPG
image/jpeg
Joint Photographic Experts Group \row
PNG
image/png
Portable Network Graphics \row
PBM
image/x-portable-bitmap
Portable Bitmap \row
PGM
image/x-portable-graymap
Portable Graymap \row
PPM
image/x-portable-pixmap
Portable Pixmap \row
XBM
image/x-xbitmap
X11 Bitmap \row
XPM
image/x-xpixmap
X11 Pixmap \endtable

Reading and writing SVG files is supported through the \l{Qt SVG} module. The \l{Qt Image Formats} module provides support for additional image formats.

Note that the QApplication instance must be created before this function is called.

See also: setFormat(), QImageReader::supportedImageFormats(), QImageIOPlugin

Definition at line 761 of file qimagewriter.cpp.

◆ supportedMimeTypes()

QList< QByteArray > QImageWriter::supportedMimeTypes ( )

static

Returns the list of MIME types supported by QImageWriter.

Note that the QApplication instance must be created before this function is called.

See also: supportedImageFormats(), QImageReader::supportedMimeTypes()

Definition at line 774 of file qimagewriter.cpp.

◆ supportedSubTypes()

QList< QByteArray > QImageWriter::supportedSubTypes ( ) const

Since: 5.4

Returns the list of subtypes supported by an image.

Definition at line 499 of file qimagewriter.cpp.

◆ supportsOption()

bool QImageWriter::supportsOption ( QImageIOHandler::ImageOption option ) const

Returns true if the writer supports option; otherwise returns false.

Different image formats support different options. Call this function to determine whether a certain option is supported by the current format. For example, the PNG format allows you to embed text into the image's metadata (see text()).

QImageWriter writer(fileName);
if (writer.supportsOption(QImageIOHandler::Description))
    writer.setText("Author", "John Smith");

Options can be tested after the writer has been associated with a format.

See also: QImageReader::supportsOption(), setFormat()

Definition at line 725 of file qimagewriter.cpp.

◆ transformation()

QImageIOHandler::Transformations QImageWriter::transformation ( ) const

Since: 5.5

Returns the transformation and orientation the image has been set to written with.

See also: setTransformation()

Definition at line 585 of file qimagewriter.cpp.

◆ write()

bool QImageWriter::write ( const QImage & image )

Writes the image image to the assigned device or file name.

Returns true on success; otherwise returns false. If the operation fails, you can call error() to find the type of error that occurred, or errorString() to get a human readable description of the error.

See also: canWrite(), error(), errorString()

Definition at line 651 of file qimagewriter.cpp.

The documentation for this class was generated from the following files:

qtbase/src/gui/image/qimagewriter.h (05fc3aef53348fb58be6308076e000825b704e58)
qtbase/src/gui/image/qimagewriter.cpp (d3dad28a51743bb408dee1cf997646a89eb6693b)

Public Types

Public Member Functions

Static Public Member Functions

Detailed Description

Member Enumeration Documentation

◆ ImageWriterError

Constructor & Destructor Documentation

◆ QImageWriter() [1/3]

◆ QImageWriter() [2/3]

◆ QImageWriter() [3/3]

◆ ~QImageWriter()

Member Function Documentation

◆ canWrite()

◆ compression()

◆ device()

◆ error()

◆ errorString()

◆ fileName()

◆ format()

◆ imageFormatsForMimeType()

◆ optimizedWrite()

◆ progressiveScanWrite()

◆ quality()

◆ setCompression()

◆ setDevice()

◆ setFileName()

◆ setFormat()

◆ setOptimizedWrite()

◆ setProgressiveScanWrite()

◆ setQuality()

◆ setSubType()

◆ setText()

◆ setTransformation()

◆ subType()

◆ supportedImageFormats()

◆ supportedMimeTypes()

◆ supportedSubTypes()

◆ supportsOption()

◆ transformation()

◆ write()